Amateur Radio. Questions And Answers

Table of contents :
About this book......Page 3
Antenna......Page 5
United States......Page 89
Legal......Page 135
Propagation......Page 143
HF......Page 163
License......Page 174
Modes......Page 177
Procedure......Page 191
Diy......Page 210
Digital......Page 223
Power......Page 235
Ht......Page 246
Software Defined Radio......Page 252
Contest......Page 264
Mobile......Page 271
CW......Page 275
RFI......Page 278
Impedance......Page 282
Transceiver......Page 288
Coaxial Cable......Page 300
Feed Line......Page 308
Receiver......Page 312
Jargon......Page 317
Uhf......Page 327
Rtl Sdr......Page 328
Equipment Design......Page 330
Safety......Page 333
Emergency......Page 335
Repeater......Page 337
Frequency......Page 339
Antenna Construction......Page 341
Satellites......Page 345
Grounding......Page 347
Phone......Page 352
Math......Page 354
Packet......Page 356
Physics......Page 358
Location......Page 360
ARRL......Page 368
Direct Conversion......Page 370
Oscillator......Page 372
Callsign......Page 374
Amplifier......Page 377
Sunspots......Page 379
Logging......Page 381
Dummy Load......Page 383
Echolink......Page 385
Tone Squelch......Page 386
Voltage......Page 390
Ehf......Page 392
Qsl Card......Page 394
Optical......Page 395
Copyright......Page 396

Citation preview

Table of Contents About this book Antenna (58 questions) United States (43 questions) Legal (28 questions) Propagation (21 questions) HF (20 questions) License (15 questions) Modes (14 questions) Procedure (14 questions) Diy (13 questions) Digital (13 questions) Power (12 questions) Ht (12 questions) Software Defined Radio (12 questions) Contest (12 questions) Mobile (12 questions) CW (11 questions) RFI (10 questions) Impedance (9 questions) Transceiver (8 questions) Coaxial Cable (8 questions) Feed Line (7 questions) Receiver (7 questions) Jargon (7 questions) Uhf (6 questions) Rtl Sdr (6 questions) Equipment Design (6 questions) Safety (5 questions) Emergency (5 questions) Repeater (5 questions) Frequency (5 questions) Antenna Construction (5 questions) Satellites (5 questions) Grounding (4 questions) Phone (4 questions) Math (4 questions) Packet (4 questions) Physics (4 questions) Location (3 questions) ARRL (3 questions) Direct Conversion (3 questions) Oscillator (3 questions)

Callsign (3 questions) Amplifier (3 questions) Sunspots (2 questions) Logging (2 questions) Dummy Load (2 questions) Echolink (2 questions) Tone Squelch (2 questions) Voltage (1 question) Ehf (1 question) Qsl Card (1 question) Optical (1 question) Untagged (1 question) Copyright

About this book This book has been divided into categories where each question belongs to one or more categories. The categories are listed based on how many questions they have; the question appears in the most popular category. Everything is linked internally, so when browsing a category you can easily flip through the questions contained within it. Where possible links within questions and answers link to appropriate places within in the book. If a link doesn’t link to within the book, then it gets a special icon, like this .

Antenna Skip to questions, Wiki by user dan-kd2ee This tag is appropriate for any question relating to an antenna. It should only be used if the question is about antennas, general questions about using or setting up a radio do not belong here, nor do general questions about reception or interference. Use this tag any time you’re asking about a specific antenna, including practical questions (how to build it) and theoretical questions (how it works). This tag is also appropriate for mounting or setting up antennas, testing antennas for SWR or with an antenna analyzer, selecting materials to use for an antenna, or questions about commercial antennas. Consider also using a more specific tag, such as: antenna-theory — for designing antennas antenna-construction — for building antennas wire-antenna , dipole , loop-antenna , vertical-antenna of antennas Related subjects: feed-line balun antenna-tuner

— for specific types

Questions Q: What are some drawbacks to delta loop antennas? Tags: antenna (Next Q) They seem to be broadbanded, small, and ground-independent relative to other cheap wire antennas, so what’s the catch? Tags: antenna (Next Q) User: bill–k5wl Answer

by adam-davis

Delta loops: Perform poorly for multi-band use, so you need a separate antenna for each band you plan on using. Require significant height for their benefits to surpass the typical dipole. Due to the shape and height the supporting structure of the delta loop is more complicated than other antenna types. These can be a small price to pay for the benefits offered by the Delta loop, but they can present significant hurdles for casual amateur radio operators. Answer

by david

Delta loops are popular on the low bands (7MHz and below) because they are much easier to set up mechanically than a quad, but they have a smaller internal area than a quad for the same frequency which slightly reduces their gain in comparison. They have a higher effective mean height when the triangle is pointing “downwards”, but this requires two points of support and is thus less common. They are strongly dependant on their height above the ground, and work best at the same height as a dipole - half a wavelength above the ground. Therefore the catch is that they are difficult to erect at a height which optimises their performance. Tags: antenna (Next Q)

Q: Are there federal laws (US) protecting antenna installation? Tags: antenna (Prev Q) (Next Q), united-states (Next Q), legal (Next Q) Are there any federal laws or FCC guidelines that allow ham radio operators to install antennas?

I live in an apartment building in a large city that bans outdoor antennas. I recall reading that the FCC protected the installation of satellite dishes and what not for consumer television usage. Are there similar protections for amateur radio? Tags: antenna (Prev Q) (Next Q), united-states (Next Q), legal (Next Q) User: brad Answer

by adam-davis

FCC 97.15(b) provides a limited amount of protection for Amateur Radio Operators who desire to erect antenna structures in the pursuit of their radio activity: Except as otherwise provided herein, a station antenna structure may be erected at heights and dimensions sufficient to accommodate amateur service communications. (State and local regulation of a station antenna structure must not preclude amateur service communications. Rather, it must reasonably accommodate such communications and must constitute the minimum practicable regulation to accomplish the state or local authority’s legitimate purpose. See PRB–1, 101 FCC 2d 952 (1985) for details.) Local and state laws and regulations governing antenna structures may apply to amateur radio antennas as well, however they have to show a legitimate purpose for the rule that specifically precludes amateur radio antenna use. Answer

by kd7kuj

In addition to 97.15, the FCC further published PRB-1 ( ) to claify the restrictions of local jurisdictions to deny permits; Several hams have been successful in getting denied building permits reversed based on this in court; Other hams have been successful in using this to prove no permit was required in the first place. That being said, this restricts local and state governments, decidedly NOT HOAs. Tags: antenna (Prev Q) (Next Q), united-states (Next Q), legal (Next Q)

Q: Why do I need to tune an antenna? Tags: antenna (Prev Q) (Next Q), impedance (Next Q) I’ve heard that when an antenna is set up, it needs to be tuned to reduce reflective power back into the radio. Is this always necessary, and if so how would I go about tuning it? Tags: antenna (Prev Q) (Next Q), impedance (Next Q) User: berry120 Answer

by michael-kjörling

There are two different parts to antenna tuning: transmission line impedance matching and resonance.

The antenna is at resonance when it presents a purely resistive load to the transmitter. That is, the reactive component of the load is 0: there exists no inductance or capacitance in the load. However, resonance says nothing about the value of the resistive component of the load. Usually, you also want to reduce the impedance mismatch, because an impedance mismatch causes power to be reflected at the point of the mismatch. Most amateur radio equipment is built to expect a resistive load of 50 ohm impedance, which is the characteristic impedance of most coaxial cables used in radio applications. An antenna tuner or ATU doesn’t actually tune the antenna; it provides a matching network. On one side the transmitter sees a nice, orderly, purely resistive 50 ohms. On the other side is an unwieldy antenna, the impedance of which at the given frequency can be anything from purely resistive at 50 ohms to some odd-ball combination of weird resistance and either inductance or capacitance. This is done by introducing either capacitance or inductance into the feedline, to cancel out the corresponding part of the load impedance. For a fixed antenna installation on a single frequency, you can even determine appropriate component values and use fixedvalue components to make up such a matching network, but that lends itself poorly to the applications in which one wants to move frequencies, antennas and so on. As a matter of fact, that is the approach taken by many electrically short antennas and it comes at the cost of reduced antenna bandwidth (because the fixed matching network can only compensate, with an acceptable SWR, within a limited range of frequencies). The SWR or Standing Wave Ratio is related to the (mis)match in impedance. This means that your perfectly resonant antenna which happens to present a nice, clean, purely resistive 150 ohms (pulling a number out of thin air here) at the feedpoint and at a given frequency will give you a 3:1 SWR against 50 ohm coax, despite being at resonance. Also, even with an ATU, it’s important to remember that the reflected power must go somewhere, and in this case, at least some of it is being dissipated as heat rather than radiated as RF. While you aren’t likely to do much harm with some reflected power from an over-the-counter 100W transceiver, this can be a serious consideration if you are running a high-powered transmitter and/or a large amplifier. Answer

by paul

Your transmitter has something called an “output impedance” and expects to be loaded with this impedance. The standard is 50 ohms. You don’t need to look up the output impedance, it was standardized and anything made in the last 50 years will expect 50 ohms. The 50 ohms the tranmitter expects is measured at RF frequencies. Many antennas look like short circuits (a loop) or open circuits (two independent wires, like a dipole) at DC, but change at radio frequencies. Modern transceivers often include an SWR meter. SWR, or standing wave ratio, should be 1 when there is no reflection. Many transceivers will tolerate an SWR of up to 2.0, but the closer this number is to 1.0, the better.

You can also buy an antenna analyzer as a stand alone instrument to measure impedance and SWR. A dipole antenna (two wires, each 1/4 wavelength, travelling opposite directions) is between 50-70 ohms for its center frequency and can often be used as-is. But you should still check it with an SWR meter or the SWR meter in your radio. Antennas that do not present 50 ohms require a circuit to transform the antenna impedance, whatever it is, to the 50 ohms expected by the transmitter output. This circuit can sometimes be made by adding funny shaped parts onto the antenna — not just any funny shaped parts, though — this is a matter for serious engineering. Other times the transformation is solved by a box called an “antenna tuner”, which remains permanently in place. You can find both manual old-timey antenna tuners and automated tuners for HF. For VHF and up, the antenna usually has an adjustable component like a slider. Tags: antenna (Prev Q) (Next Q), impedance (Next Q)

Q: How does moving a feedpoint off-center in a dipole affect the resonant frequency and resistive load? Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) Specifically, I understand that OCF dipoles change the SWR, but does it do this via reactance or resistance, or both? Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) User: bill–k5wl Answer

by phil-frost

I’m going to assume we are discussing ideal, resonant dipoles. Consider what’s happening inside the dipole. Say you are transmitting a carrier. Say at one point in this carrier’s cycle, the voltage is shoving all the charge carriers to the left. What makes the dipole resonant is this: those charge carriers get pushed down the wire. As the approach the end, they get compressed because they have nowhere to go. This over-abundance of charge carriers means a high voltage at the end of the wire. They can’t shoot out the end of the wire, so they bounce back. In a center-fed half-wavelength dipole, they reach the feedpoint, after having bounced off the end, at precisely the time that your transmitter has changed phase 180 degrees, and is now trying to push the charge carriers in the other direction. Thus, the natural bouncing back and forth action in the antenna is precisely in phase with the transmitter, helping it to move more current, with less voltage. This explains two things on the FCC test: the voltage distribution in a half-wave dipole is highest at the ends and lowest in the middle the current distribution is highest in the middle and lowest at the ends

We know that our center-fed half-wavelength dipole has a feedpoint impedance of 75Ω. That means, at the feedpoint, that for every ampere, there are 75 volts (think Ohm’s law). This is true both of RMS measurements, and any instantaneous measurement. This last bit, that the instantaneous current or voltage at any time also have a ratio of 75V to 1A (that is, 75Ω), is just another way of saying that the feedpoint impedance is purely resistive. Our ideal dipole doesn’t actually have any resistance: this resistance is the radiation resistance of the antenna. The antenna creates the illusion of a pure resistance from a tuned system of reactive components, which, at resonance, cancel each other to leave only a resistive impedance. But what if the feedpoint isn’t in the center? This actually doesn’t change the resonant frequency; it just changes the impedance, which remains resistive. Consider what happens if we move the feedpoint just a little closer to one end. But, we also get farther from the other end. We know that in the center of a halfwave dipole, current is at a maximum. This makes sense, because after the charge carriers pass the center, they are now closer to the other end, building up voltage there, which serves to slow them down. So, if we aren’t in the center, we get less help with current, but we get more help with voltage. That is, impedance goes up. We can couple energy just as efficiently into this antenna, provided we can match its impedance. The common choice of the center of a half-wave dipole is usually selected because it’s close enough to 50Ω coax that losses are acceptable without any additional matching. Wikipedia gives the math to calculate the impedance at an arbitrary point for a halfwave dipole: 75 Ω Rr = sin 2 (2xπ/λ) Where: x is the distance from the end of the dipole, and λ is the wavelength (twice the length of the dipole). For example, say we have a dipole for λ = 100 m . Fed at the center, x = 25 because this half-wave dipole is 50m long, so the middle is half of that, 25m from the end: 75 Ω = 75 Ω Rr = sin 2 (2 ⋅ 25 ⋅ π/100) Fed 1/3rd of the way from the end, x = 50/3 = 16.67 : 75 Ω = 100 Ω Rr = sin2 (2 ⋅ 16.67 ⋅ π/100) Further reading: Dipole antenna feed impedance, 200 Ohm Feed Point Off-centre Fed Dipole,

Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q)

Q: Should I chose a vertical or a horizontal HF antenna? Tags: antenna (Prev Q) (Next Q), hf (Next Q) If I only have the budget for one HF antenna, should I chose a vertical or a horizontal antenna? Tags: antenna (Prev Q) (Next Q), hf (Next Q) User: timtech Answer

by on4aa

Summary If you can have only one antenna and can chose between a vertical HF antenna or a relatively high horizontal HF antenna, go for the horizontal antenna. Modelling results In January 2008, L. B. Cebik, W4RNL (SK) published what was going to be the last entry of his seminal 10-10 News series. It turned out to be an interesting gain comparison of single element 28.4MHz antennas modelled over various ground types of which a summary is presented here (Table 1). His findings seem to fit well with what John Devoldere, ON4UN modelled and published for equivalent antennas on the lower HF bands .

Horizontal HF antennas: near-by ground gain At a height of about λ/2, the nearby ground reflection of a horizontal HF antenna will start to be constructive at interesting take-off angles for long- distance ionospheric contacts.

This will provide a net gain over the antenna in free-space. Vertical HF antennas: near-by ground loss This is not the case with vertical HF antennas. Nearby ground only contributes loss. This even more so when the ground forms part of the return path of the radiating structure. Even when far-away ground reflections may cause the directivity of a vertical HF antenna at low take-off angles to be much higher than that of a horizontal HF antenna, its net gain will still be lower at those angles. This makes the horizontal HF antenna a clear winner, at least for what transmission is concerned. Note that gain and directivity are not synonyms; gain takes into account losses, directivity does not. Vertical HF antennas still remain useful Vertical HF antennas do have their merit though. At the lower end of the HF spectrum, the λ/2 height requirement for horizontal antennas can become cumbersome (even though a horizontal phased array may weaken this requirement by allowing somewhat lower heights). A vertical HF antenna can get away with a height of only λ/4. Furthermore, the directivity of a vertical HF antenna can be effectively employed at the reception end to cancel out high-angle interference by near-by stations. This is why some stations use receive-only phased-arrays of verticals on the low bands. Polarisation at HF Polarisation is not really an issue at HF (apart from lightning and man-made noise considerations). This is so because the ionosphere is mainly an anisotropic medium, i.e. it messes up polarisation. Answer

by dan-kd2ee

It doesn’t really matter


You’re asking about a topic called polarization, which is really important in VHF and UHF. It’s the reason why rotating your HT can improve or harm your reception, and it’s also the reason why some 3D glasses and sunglasses work. But because of the way HF propagation works, it doesn’t really matter. Any ionospheric propagation gets the polarization randomized anyway. Very short range (ground wave) HF works best with a vertical antenna, but it’s very rare that you care more about short-range than long-range. In terms of limited space and cost, it’s probably easier to set up a horizontal antenna (or an inverted V like a G5RV or OCF) than a vertical simply because it’s easier to string a wire through some trees than it is to secure a flagpole or tower against gravity and wind loads. Tags: antenna (Prev Q) (Next Q), hf (Next Q)

Q: Calculating Antenna Length on the FCC Exam vs. in Reality

Tags: antenna (Prev Q) (Next Q), united-states (Prev Q) (Next Q), math (Next Q), physics (Next Q) I have seen the following formulas for calculating half and quarter wavelength antennas: Formula for 12-wavelength antenna (in free space): Length (feet) =

492 f MHz

Or is it… Length (feet) =

468 f MHz


Formula for 4-wavelength antenna (in free space): Length (feet) =

246 f MHz

Or is it… Length (feet) =

234 f MHz

Or is it none of the above? I believe the US FCC Technician class exam requires the use of 468/f. Are any of these equations helpful in calculating antenna length in reality, or is this only in theory for the exam? What additional factors should be taken into account, if any? What would be a better equation if none of the above? Tags: antenna (Prev Q) (Next Q), united-states (Prev Q) (Next Q), math (Next Q), physics (Next Q) User: dan Answer

by walter-underwood-k6wru

The 492/f formula is for an ideal antenna in free space, the 468/f is an estimate for real antennas at a reasonable height over ground. The 492/f formula is a conversion from metric units to English units for the fundamental frequency and wavelength (λ ) formula. c = 3 × 108m/s (the velocity of light) and f = frequency — c λ= f This gives the length of a full wavelength in meters. This formula is correct if the conductor is infinitely thin and other objects are infinitely far away from the antenna. The length of a real, installed antenna is affected by the diameter of the conductor (not a big effect for wire antennas) and the height above ground (a big effect). Capacitance to ground electrically shortens the antenna, so less wire is needed for resonance.

468/f is a good estimate for wire antennas at HF less than a wavelength above ground. This is an empirical formula, so there is no mathematical derivation. The 468/f formula was first published in the 1929 ARRL Handbook. It is probably based on experience with 40m and 80m antennas at heights of 1/4 to 1/8 wavelength above ground, since those were common antennas at the time. A November 2009 QST article by Ward Silver, N0AX, measured a 20m dipole at heights from 1/8 to 2 wavelengths and found the length varied from 466/f to 481/f depending on height. He recommends starting with a wire length of 490/f and expecting to shorten the antenna to resonance. Most wire antennas need length adjustment for resonance after installation, because of the capacitance to nearby structures or trees, or local ground conductivity. It is much easier to shorten an antenna than to lengthen it, so it is a good idea to cut the antenna wire a little long. For more on this publication history of this formula, see this article by N0AX


For more information about wire antennas, I would start with Chapter 21 of the ARRL Handbook. For details, read the ARRL Antenna Book. Answer

by pearsonartphoto

For someone who knows how to convert between inches, feet, and meters, it’s really quite simple. You only really need to know one formula to do it all, and that formula is 300 = f × wavelength . If you find the wavelength for the given frequency, then just find the type of antenna (quarter-wave), take the appropriate fraction of the wavelength, and convert said quantity to the appropriate units. For example, the wavelength for a 146 MHz signal is 2.05 m, multiply by 39 and you have 80 inches. If you want a quarter wave whip, then your antenna is 20 inches long. As to where this applies after the test, it does apply, but there is one huge catch. The antenna needs to have the provided wavelengths electrically, not physically. What does that mean? Basically, there’s a quantity known as Velocity Factor which takes into account how fast the waves move in the metal. However, most metals have a permittivity of about 1, making the electric distance equal to the physical distance. Some non-metal antenna materials could be different, however, so be warned. Also, cable is different, etc. Essentially, if the velocity factor of an antenna is 2, then an antenna could be made with half of the length and still be resonant. However, as the velocity factor for most metals is 1, and there are other reasons to use metal as antenna building material, this isn’t usually a significant factor. It does make a small difference in certain types of phased antennas, however. As to your specific question, the half-wave formula is (3.28/2)(300/f) , or 492/f , and the quarter wave is similarly (3.28/4)(300/f) or 246/f . This applies if the velocity factor is 1, which only holds true if the antenna is far away from conductive surfaces, including the ground. The distance required is at least 1 wavelength away typically. Answer

by dan

Legend c = velocity of propogation = speed of light (299,792,458 meters/second) f = frequency λ = wavelength Formulas The basic formula for calculating wavelength is: c λ= f To make the math simpler, frequency (f ) is expressed in megahertz (MHz) and the velocity of propogation in free space (c) for frequencies above 30 MHz is expressed as and rounded to 300 megameters (Mm). This will return a wavelength (λ ) in meters. So for 1 wavelength above 30 MHz: 300 λm = f MHz However, when f < 30MHz , the velocity of propogation (c) is expressed as and rounded to 286 Mm because “[e]lectrical wave propagation in wire is about 95% to 97% the speed of light. Since wavelength is most commonly used for building antennas which involve conducting the wave from air into the wire and vice versa, the calculation is adjusted assuming the slower propagation in an unshielded conductor. “However, this 3% to 5% discrepancy is small enough at frequencies above 30 MHz that it is usually ignored for simplicity, and 300 Mm is used instead” (Adam Davis, KD8OAS). When f < 30MHz the discrepancy becomes more significant and the adjusted value, approximately 95% of 300 Mm, is used instead, which is approximately 286Mm (which would actually be 0.95¯3). This results in the following formula for 1 wavelength below 30 MHz: 286 λm = f MHz To convert this into feet, multiply c by 3.28084, which results in the following formula for receiving an answer in feet when f > 30MHz : λ ft =

(3.28084)300 984.252 = f MHz f MHz

This is rounded down to 984/f for the sake of simplicity. However, recall that when f < 30MHz , the velocity of propogation (c) is expressed as and rounded to 286 Mm. Applying this formula results in the following for converting this into feet below 30 MHz:





λ ft =

(3.28084)286 938.32024 = f MHz f MHz

This is also rounded down to 938/f for the sake of simplicity. Calculating for half and quarter waves is just a manner of of dividing c/2 or c/4 , respectively. So we end up with the following calculation for calculating the length of half wave antennas in feet when f > 30MHz : (3.28084)(300/2) 492.126 λ ft = = f MHz f MHz When calculating the length of half wave antennas in feet where f < 30MHz , we have the following formula: (3.28084)(286/2) 469.16012 λ ft = = f MHz f MHz But this is generally expressed as 468/f , not as 469. Why is this? First of all, remember that the velocity factor is approximately 95-97% of the speed of light, so adjusting this value results in slightly different results. Also, whether we use the adjusted value of c when f < 30MHz (286 Mm) or apply the velocity factor directly to c will slightly alter our result. So for instance, the following calculation will get us closer to 468/f : (3.28084)((300/2)(0.95)) 467.5197 λ ft = = f MHz f MHz This would round up easily to 468/f when f < 30MHz , and it is slightly more accurate. This shows why there are different equations and when each should be used. Tags: antenna (Prev Q) (Next Q), united-states (Prev Q) (Next Q), math (Next Q), physics (Next Q)

Q: Can I have multiple inverted-vee antenna fed by a single coax? Tags: antenna (Prev Q) (Next Q), antenna-construction (Next Q) A friend who recently received his call is planning to setup an inverted-vee for 40/20m bands. Our take is the signal will take the path of least impedance into the correct length antenna wire. Something like the image attached; it depicts two wires running right next to each other. The tab in the middle of the wire marks the end of the 20M, the other tab marks the end of the 40M length.

Can the antenna wires for both bands be fed at a common point by the coax? Tags: antenna (Prev Q) (Next Q), antenna-construction (Next Q) User: vu2nhw Answer

by walter-underwood-k6wru

Yes, this works fine. It is often called a “fan dipole”. There are separate resonant dipoles for each band, all fed from a common point. The wires should be separated by a foot or more. If you have enough tie points at the ends, you can run them in slightly different directions. The resonant dipole will have a low impedance, around 50 Ohms. The non-resonant one will have a higher impedance and will not accept much signal. The antennas will interact with each other, so you may need to tune them to length iteratively. Most people start by adjusting the length of the longer antenna first. The 40m antenna will also be close to resonance on 15m, so you can probably use it on that band with an antenna tuner. Tags: antenna (Prev Q) (Next Q), antenna-construction (Next Q)

Q: What gain do I need to talk to SO-50 with my HT? Tags: antenna (Prev Q) (Next Q), ht (Next Q), satellites (Next Q) My HT has 5 W of power, a sensitivity of about 0.2 µV, and I would like to talk to the SO50 with it. How much gain do I need in my antenna to make this work?

Tags: antenna (Prev Q) (Next Q), ht (Next Q), satellites (Next Q) User: pearsonartphoto Answer

by pearsonartphoto

The specifications from AMSAT for the SO-50


The repeater consists of a miniature VHF receiver with sensitivity of -124dBm, having an IF bandwidth of 15 KHz. The receive antenna is a 1/4 wave vertical mounted in the top corner of the spacecraft. The receive audio is filtered and conditioned then gated in the control electronics prior to feeding it to the 250mW UHF transmitter. The downlink antenna is a 1/4 wave mounted in the bottom corner of the spacecraft and canted at 45 degrees inward. So, what does all of that mean? First of all, the 5W signal you send has to make it to the spacecraft and be received. Let’s just assume a uniform gain from the spacecraft to start with. Let’s also start with a uniform gain from the HT. The satellite footprint is about 3000 miles, so let’s just say the maximum distance to the satellite is 2500 km, accounting for height and the radial distance. It should be close enough to get an idea. That means the one way path loss is about 128 dB. That means your signal would need to be at least 100W to be received, given no gain, as can be calculated by 10128−124 10 × 1000 Bottom line, you need a gain of at least 12dB to make the satellite, and a bit more margin would be helpful. As far as the receiving, that’s where things are a bit trickier. The power can be found by V V R R , and also converting the from peak to RMS. is usually 50 ohms. When you take all of that in to account, the specified minimum detection for the signal is 2

⎛ ( 0.2e−6 ) √2 −124 log10 ⎜⎜ 50 ⎝


⎞ × 1000⎟⎟ × 10 ⎠


(Basically, find power R , convert to mW, and convert to dBm). The satellite signal is only 250mW, and you’re looking at the same path loss of the signal. The gain required is 10 ×10 10 × log10 ( 250mW ) , or about 26 dB. This is quite difficult to achieve, and usually 128−124

requires a pre-amp to be effective, or a really good antenna. Bottom line- Tx is 12dB, Rx is 26 dB, at max distance, and less for an overhead pass. Tags: antenna (Prev Q) (Next Q), ht (Next Q), satellites (Next Q)

Q: What is the relationship between SWR and receive performance?

Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) If an antenna analyzer shows 1:1, does that mean it’s an ideal receiver as well? And what about the converse, will a well performing receive antenna show a 1:1 SWR? I’ve wondered this for a while, sometimes I want a wide band antenna just for listening, and I am not clear about this relationship. Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) User: k9krb Answer

by michael-kjörling

If an antenna analyzer shows 1:1, does that mean it’s an ideal receiver as well? No. Assuming we’re talking about a characteristic impedance of 50 ohms, a 50 ohm resistor (otherwise known as a dummy load) will show a SWR of 1:1, although it will almost certainly perform very poorly as either a receive or transmit antenna. The low SWR simply tells you that there are no impedance mismatches along the path from the transmitter (antenna analyzer in the case of your question) to the antenna feedpoint, at the current operating frequency. And what about the converse, will a well performing receive antenna show a 1:1 SWR? Yes and no. Yes, a SWR of 1:1 means that you aren’t losing signal to impedance mismatch reflections. No, another issue is how efficient the antenna is at picking up the (desired) signal, preferably (especially in the case of directional antennas) while rejecting undesired signals as well. An antenna that is 5% of a full half-length dipole isn’t going to pick up as much RF as the full-length dipole, let alone a full-sized directional antenna pointed in the proper direction, simply due to the much smaller physical (antenna aperture) size. Generally speaking, if an antenna analyzer or (other) transmitter shows that the antenna output presents a SWR of 1:1, then what you have is probably about as good as it gets. That does not necessarily mean that what you have is a good antenna setup as exemplified by the extreme example of a dummy load. Answer

by phil-frost

Simplified answer: There is no relationship between SWR and receive performance. There is one condition for this simplification to be true: the received RF noise floor must be above your receiver’s noise floor. Beyond this, anything you might do to increase the output from the antenna does nothing to increase the signal to noise ratio , which is a

better measure of receive performance. SWR is a measure of the impedance mismatch between your antenna and transceiver. Whether transmitting or receiving, a higher SWR correlates with a less efficient coupling of energy between the transceiver and antenna. This inefficiency is problematic when transmitting because it can make a lot of heat, and it limits one’s ability to overcome noise at the intended receiver. We could compensate with an amplifier, but high-power amplifiers are expensive, and big, and hot, etc. However when receiving, losses are easy to overcome. The heat generated is insignificant, and at the extremely low power levels involved in receiving, amplifiers are not large or expensive or difficult to design. Remember also that losses attenuate the signal, and also the noise equally. Improving the SWR will increase the power received, but this is signal and noise, and thus does nothing to make the signal more intelligible, unless both are attenuated so much that most of the noise is no longer coming from the antenna, but instead from the electronics of the receiver. At HF, low-noise amplifiers are easy to design, and the ambient RF noise floor is relatively high, so antenna efficiency (including SWR-related losses) is not usually the limiting factor in receive performance. If you want a wide-band antenna for receiving, then you may do well with a non-resonant antenna. Such an antenna will be very inefficient, but this easily compensated with a lownoise amplifier. Because it is not operated at resonant frequencies, bandwidth is hardly a concern. A small loop or its electrical dual, the Hertzian dipole could work. Or, consider a Beverage antenna if you want directionality, which does increase signal-tonoise ratio, provided it’s pointing in the right direction. Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q)

Q: Does a tube based HF transmitter need an antenna tuner? Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q) With the adjustments on a transmitter such as a Yaesu FT-101E, is there any purpose for an antenna tuner, or can you accomplish the same thing by adjusting the loading and other controls? Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q) User: k9krb Answer

by oh7lzb

The original Yaesu FT-101 tuning instructions

state the following:

Do not use antennas which are untuned or exhibit an SWR of more than 2:1. An external antenna tuner can usually work with a much broader mismatch range. If you have a “random wire” or otherwise untuned antenna, a tuner is clearly required. A slight mismatch (2:1 or less) can be handled by the tube amplifier’s controls. The same advice will apply to other tube finals. Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: How do you RF-ground an antenna? Tags: antenna (Prev Q) (Next Q), propagation (Next Q), rfi (Next Q), grounding (Next Q) I don’t understand how you would go about giving an RF ground to your antenna. Would it not become an additional radial and affect the signal? What is the proper way to ground your stations antenna? Tags: antenna (Prev Q) (Next Q), propagation (Next Q), rfi (Next Q), grounding (Next Q) User: david-anastasio Answer

by wprecht–ab3ry

To answer your first question, yes, it will affect the signal, but it’s a good thing. What you do to (RF) ground your antenna(s) depends on what type of antenna you are using. For instance, dipoles do not require a ground. Typical vertical antennas do require a graound though some types such as the GAP Challenger use 3 wires insulated from ground (in this application they are referred to as a counterpoise). In a typical vertical antenna installation, your radiator is λ/4 tall (electrically at least, it might be physically shorter through the use of coils or whatever). This is referred to as a monopole and is half of a good antenna. You make the ground be the other half of the antenna but creating a ground plane with radials. This creates a virtual image antenna that

completes the overall antenna effect. These radials are usually buried just below the surface or stapled down to the ground and grass is allowed to grow through them to hold them down. That’s your RF ground. In addition, it’s usually desirable to have an electrical ground for lightning and static electricity protection. This is achieved by making a lower impedence path to ground than you feedline presents. Usually one or more 8’ copper-clad rods are pounded into the ground at the base of the antenna and bound to it. The area of effect of this is below the ground plane and doesn’t detract from the signal. Tags: antenna (Prev Q) (Next Q), propagation (Next Q), rfi (Next Q), grounding (Next Q)

Q: How to calculate power loss between radio and antenna Tags: antenna (Prev Q) (Next Q), power (Next Q), math (Prev Q) (Next Q) I have a 5W HT that only kicks out about 1W by the time it hits my antenna (which I understand is the norm). How do I go about calculating power loss in various equipment? Tags: antenna (Prev Q) (Next Q), power (Next Q), math (Prev Q) (Next Q) User: dan Answer

by dan-kd2ee

There are a few possibilities. First of all, in larger assemblies (mostly important in repeater design) each component will have a parameter called insertion loss. This is the loss, in dB, through that componenet the loss caused by inserting that component in your feed line. Filters have insertion loss, as do duplexers, and even inline wattmeters and adapters, although the last two should be pretty low. Typically this is about 0.5 dB for each filter or other component, at least in the installations I’ve seen. Then you need to add in loss due to feedline. Different types of feed line have different losses at different frequencies. For example, to get the loss you’ve described (5W to 1W), and assuming a UHF HT in the 440MHz band, and 50 feet of RG-58 coax (a common small diameter coax) equates to about 5.6dB. This is a parameter that you would look up in a table or a graph from the manufacturer of the coax you’re using. You may also have some loss at the antenna itself. Especially “rubber ducky” antennas, which are electrically shorter than a true quarter wave antenna and compensated with loading coils, will have a certain amount of loss, also computed in dB. This basically accounts for the reactive and resistive losses in the antenna, decreasing the actual emitted power. Finally, to calculate your actual radiated power, you can simply add up all these values. Every 3dB equates to cutting your signal in half, and 10dB equates to one tenth of your original power getting out. You would compute the actual power by multiplying your transmitter’s power by 10(−loss (in dB)/10)

Tags: antenna (Prev Q) (Next Q), power (Next Q), math (Prev Q) (Next Q)

Q: Has a vehicle magnetic antenna mount ever caused a road accident? Tags: antenna (Prev Q) (Next Q), mobile (Next Q), safety (Next Q) Some people believe that mag mount magnets lose their effectiveness over time, eventually causing a dangerous situation as the antenna could rip loose from the vehicle and become a projectile or distraction at an unfortunate time — e.g. on a highway due to air forces or perhaps at a stoplight under heavy braking. Mitigating these concerns are the fact that the antenna is still attached by coax and that I personally have never seen it mentioned in the news nor have I heard of any traffic laws prohibiting mag mount antennas on a vehicle. Still, with safety in mind, I use the screw in trunk lip mounts. Should I keep telling my friends to stay away from the mag mounts or are these supposed dangers merely paranoia and urban legend? Tags: antenna (Prev Q) (Next Q), mobile (Next Q), safety (Next Q) User: paul Answer

by oh7lzb

Magnet mounts can come off, and they do fall occasionally. I can’t quote any statistics, but it has happened to me twice in the past - tall HF antenna combined with too small magnet mount and high speed. Luckily the cable held the thing on the roof. Short VHF/UHF sticks (think 1/4 wave for 2 meters) would never fall with the same mount - the wind load is just so much smaller. For my irregular HF use, I’ve switched to a larger magnet mount and thinner vertical, and the constantly used VHF/UHF sticks are drilledthrough. There are also stories of shattered glass (antenna comes off and hits your own back window) and scratches on roof. If the antenna fell down and stopped in the middle of a highway, it would be dangerous to a motorcycle, but less of a hazard to a car. It might break a tire, which in turn could lead into a more serious accident. A thick HF antenna could puncture a car somehow. Large magnet mounts are heavy, and one could bounce higher into air and penetrate a wind shield. In an accident it would probably get loose and fly away, but it would have the same velocity as the much heavier car, and the damage caused by the car would probably be dominant. If you loose one of these on a road, do go back and pick it up immediately. If you loose one on a highway, in many places it’s both dangerous and illegal to stop and go pick it up yourself, so you might have to call the police for assistance. Wikipedia has some information on how magnets can be demagnetized . Permanent magnets are made from “hard” ferromagnetic material which are very hard to demagnetize. Magnets on the roof are unlikely to get hot enough to degauss (140 °C / 280

°F for neodymium, 300 °C / 570 °F for ferrite and SmCo), and they’re not subject to strong external magnetic fields, either. Hammering or jarring - some vibration is going to be present, and after a very long time that might have some effect, but that’s just my guess. Typically a mag mount will be decommissioned quick enough that demagnetizing should not be a concern. Water tends to get into the connectors and cables, and the cables break from stress under doors. Magnet mounts are very popular. I don’t remember any documented serious accidents with them. If accidents would happen, there would be articles on the amateur magazines, blog posts, and pictures on the Internet. I would claim they’re pretty safe, if the relation between antenna size, mag mount strength and vehicle velocity are in a good balance. Tags: antenna (Prev Q) (Next Q), mobile (Next Q), safety (Next Q)

Q: Antenna modeling on non-uniform terrain Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q) I’m interested in modeling the radiation pattern of wire antennas for hf before I invest the resources necessary to erect the antenna. I’m familiar with tools such as 4nec2, but from what I can tell the ground is modeled as being flat. However, at my house, the terrain is sloped at roughly 25 degrees. My intuition says that this will affect the radiation angles of radiation. How can I model antennas to include local terrain? Would a useful representation be rotating the antenna 25 degrees to account for the terrain? Does it really matter? Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q) User: w5vo Answer

by phil-frost

Would a useful representation be rotating the antenna 25 degrees to account for the terrain? I’d think so, as long as you also then rotate all the results 25 degrees in the opposite direction. I can’t think of anything that actually wouldn’t rotate with the ground (gravity, geomagnetic field, …) that would have any significant effects. Does it really matter? No doubt the 25 degree slant will significantly affect many antenna designs. Not only will you have a hard time transmitting through a mountain, but the ground will form an image antenna as if it were a mirror, creating a phased array. Turning the mirror 25 degrees will make a big difference. Of course, probably there’s nothing you can do about it. Maybe you will feel better not knowing.

Besides, there are plenty of other things that can make a big difference. Modeling results can be very wrong if they don’t include everything near the antenna: the tower, the feedline, your gutters, trees, etc. Ground conductivity can change with weather. Then, the ionosphere swirls around and messes the whole thing up. So, from a practical standpoint, modeling can only solve some of the problems involved with making a good antenna. My personal approach would not bother with modeling. I have a trapped vertical that wasn’t too expensive and covers enough bands that one of them is always open. If you have the space, a couple of parallel-fed simple dipoles would probably work as well for less cost. I put in plenty of radials to keep the ground losses low, and tuned it carefully. The idea is to focus on radiating, and not where I’m radiating. I wouldn’t win any DX contests, but I have no difficulty making an international contact any day. Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: Do I need a SWR meter for a basic 2 meter antenna? Tags: antenna (Prev Q) (Next Q), ht (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q) I have a 5 watt 2 meter handheld transceiver and want to build a helmet with an antenna, microphone (with VOX enabled) and earpiece for the radio. For the antenna part, I just want to do something simple like a wire at the right length. I’m 15 and saving for so much other stuff (like a signal generator, bench power supply etc.) and can’t really afford an SWR meter. Tags: antenna (Prev Q) (Next Q), ht (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q) User: skyler-440 Answer

by james-nf8i

At power levels that low, you probably don’t need an SWR meter permanently installed. You will find it useful to have an SWR meter or antenna analyzer available when building the antenna, though, to ensure it is properly operating on your chosen frequencies. Perhaps you can borrow one from a friend, mentor, or local radio club to use while building your kit? Tags: antenna (Prev Q) (Next Q), ht (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q)

Q: How much RF energy do trees and branches absorb? Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q) For the 20m - 10m and 6m bands, will having my dipoles below the tops of trees (I live in redwood forests) drastically affect the RF power out or radiation patterns of my dipoles if

I can still get them at least 1/4 wavelength above the ground? Or will the greenery absorb and/or distort the radiation patterns? Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q) User: gdc Answer

by phil-frost

Trees do absorb some RF energy. So do buildings, hills, and other structures. There are very few cases where higher isn’t better for antennas. However, I’d guess that most amateur radio dipoles are below the treetops. Will some energy be lost? Yes. Will the antenna still work? Absolutely. Without the specifics of yours trees, and your antenna, we can’t say exactly what effect trees will have, but it’s a fair guess that the absorption by trees will be somewhere between negligible to significant but probably not drastic. Part of the reason trees aren’t a huge problem is that at HF, they are electrically small. That is, their size is smaller, relative to the wavelength of interest. Longer wavelengths pass through things more easily, such as the thumping bass through those annoying cars. So, get your antenna as high as you can, but if you don’t have a tower sticking above the redwoods, don’t worry. Your antenna will still work. Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q)

Q: What is the correct procedure to beam long-path? Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q) I’m new to directional beam antennas, and saw that K9W Wake Island DXpedition was working 10 meters “long-path” at 1230z, or 6:30a.m. in Texas. This was late enough for the sun to be coming up, but is it even possible to make the “long path” connection that far around? I would have thought Wake Island was totally in the dark at that time. More generally, what is an ideal situation for long path, and is it simply a matter of pointing 180 degrees away from the listed direction on Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q) User: bill–k5wl Answer

by wprecht–ab3ry

You are correct, the long path azimuth is simply 180 from the bearing listed in QRZ. Whether it’s going to work depends on a number of varibles: your power, your antenna, their antenna, the band, atmospheric conditions, the time of day, the terrain on the path and probably a few others I have forgotten. Doing 10m, a “daytime” band long path to the east at local dawn might work given favorable propigation conditions. And the fact that when 10m is open, it can be really

open. I have never made a long path QSO personally (well, on purpose anyway), but those folks that do work that way seem to be working “diagonally” if you will. For instance, the long path to Europe from Australia is mostly over ocean (salt water being good for this). And don’t forget the great circle route is the true route you are looking at here, not the obvious “straight line” paths you see on flat maps. Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q)

Q: Can I reduce RFI/noise at the antenna? Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q), rfi (Prev Q) (Next Q) Recently, the power was out in my neighborhood for an extended period of time. I fired up my HF rig using battery power and was amazed at the lack of noise across the HF bands. When the power grid came back online, the noise returned. The difference was drastic. S2 vs. S9 drastic. With that said, is there a good way to reduce RFI/noise at the antenna? Specifically a dipole antenna? Is there a better way to solve this problem? The houses are packed so close together in my neighborhood, the likelihood of eliminating the noise at the source(s) is nil. For reference, the type of “noise” I’m hearing is more of a white noise rather than a noise pattern coming from an interfering appliance. (Though, I do hear RFI with a pattern to it from time to time on certain bands as well.) Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q), rfi (Prev Q) (Next Q) User: the-driver Answer

by phil-frost

First, I’d be sure it’s actually the antenna picking up the noise, and not something else. If you don’t have a balun on that dipole , probably your feedline is picking up all the noise in your house. Any other wires attached to your receiver can also make good noise antennas, especially the power cord, which is attached to your home’s wiring, and coupled to all the noisy stuff running on it. Get some ferrite beads designed for EMI control, and start snapping them on any wire attached to the receiver. Keep snapping them on until you stop getting improvement. If you have cooperative neighbors, do the same to their noisy electronics. Ferrite beads work for keeping EMI out of your receiver, and also for preventing it from leaving the source in the first place. Once that’s done, the next thing is to get the antenna as far away from other noise sources as possible. Powerlines, neighbors, etc. Put it on the tallest tower allowed in your neighborhood. In urban areas, your options are limited, but do what you can.

The rest is just trying to null the noise based on its direction, or it’s polarization, or something else. Every antenna has a particular polarization and radiation pattern. You don’t know the same of your noise sources, but just by playing with the orientation of the antenna you might by chance find an arrangement that works well. Try not to be parallel to power lines, etc. A directional antenna helps, but is probably impracticably large at HF. At this point, you are running out of options. Some of the noise is in the far field antenna, and there just isn’t much you can do about this besides move.

of the

Other noise is in the near field, which at HF, can be quite big. In this region your antenna isn’t acting as an antenna, but rather one winding of a transformer, or one plate of a capacitor. There is one additional game you can play here that might help. Remember that electromagnetic radiation is made of two fields: an electric field and a magnetic field. In the far field, these two are inseparably linked, related by the impedance of free space . However, in the near field, you can have a strong electric field and a week magnetic field (capacitors), or vice-versa (transformers). You can build different antennas which, at some distance in the near-field, have a different sensitivity to one type of field or the other. W8JI has a good article on small loop antennas , and describes this in some detail. In particular, there’s this great graph:

A high impedance means the antenna is more sensitive to electric rather than magnetic fields. So, you can see that if your noise source is very close (less than 10 meters for this

antenna) and is largely E-field noise, you’d want a loop. However, keep in mind: the impedance of all antennas are identical and equal to the impedance of free space (377Ω) in the far-field. This only makes a difference for noise sources in the nearfield, which couple to your receiver by mutual inductance or capacitance, not EM radiation. the impedance changes up and down in the near-field with distance, and if a particular antenna seems to have less noise, it’s due to chance and your particular noise source’s characteristics, not some magical “noise immunity” intrinsic to some antenna design. That said, most people already have dipoles, so if they find them noisy, sometimes they have luck switching to a loop, which provides a complementary near-field impedance, and just might be better in a particular environment. Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q), rfi (Prev Q) (Next Q)

Q: How can I safely transmit without an antenna tuner or SWR meter? Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) Just what the title says. An Antenna Tuner , henceforth AT, is almost a de facto piece of equipment in a shack; working the bands without one is tantamount to leaping off the diving board into a swimming pool with tarantula nests in it … or worse. The reason for the AT is primarily to match the antenna to the transmitter for the Standing Wave Ratio . The greater the SWR, the more the risk to the transmitter. But before one uses an AT, one either designs the antenna (balanced/unbalanced, array-type, length, impedance … and constructs it), or purchases the antenna. Keeping it simple Say, A simple mono-band centre-fed dipole is constructed after calculating the length for that band Say further, neither an AT nor an SWR meter is available Given the above assumptions, what I would like to know How can I transmit without an antenna tuner? Are there any rule-of-thumb tests/calculations I may do to determine whether an antenna is a decent fit for a given band? As a corollary What if the antenna is not a simple centre-fed mono-band antenna?

How did they tune antennas back when the hobby was still new? I guess Does a tube based HF transmitter need an antenna tuner? may be relevant to this part of the question Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) User: vu2nhw Answer

by adam-davis

The SWR meter helps you match the impedance of the radio to the antenna. If the impedance is mismatched, you lose power. If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies. Tube based transmitters and amplifiers have more leeway for mismatch than semiconductor based amplifiers. Lower power transmitters also have more leeway for mismatch before damage occurs. The ideal is to borrow an SWR meter and tune your antenna for the intended frequency, or send the antenna to someone who can do that for you. If you don’t have any of these tools and can’t get help from others easily, you can get as close to the right frequency by building the antenna according to the design, then start transmitting on low power and make contacts. Find someone willing to work with you, and ask for signal quality reports. Then make a small adjustment to the antenna and ask for another report. It’s a long process, but they will receive more signal the better your radio is matched to your antenna, so it’s an easy check. Do this at low power though, so you reduce the risk of damaging your transmitter. Answer

by phil-frost

How can I transmit without an antenna tuner? Simple. You use an antenna that’s already tuned. There are plenty of radios that operate without any tuner. For example, basically every VHF radio. One reason for this is that most VHF antennas are purchased rather than manufactured by the amateur, and the antenna manufacturer has already tested and tuned the antenna design. It’s also relevant to mention that an antenna tuner doesn’t actually make the antenna tuned. With a perfectly matched antenna (SWR 1:1), all the power sent down the feedline by the transmitter will be accepted by the antenna and radiated away. When the antenna isn’t perfectly matched, some of the power is accepted by the antenna, and some is reflected back at the transmitter. When it reaches the transmitter, the transmitter’s RF amplifier has to work against this reflected power, which can cause transistors to overheat or protection mechanisms to reduce the transmit power. By inserting a tuner between the transmitter and the feedline, the power reflected back from the feedpoint is then reflected again back at the antenna. The transmitter now does

not have to work against this power, and it sees a well-matched load. However, the power is still being reflected back-and-forth between the feedpoint and the tuner, encountering losses in the feedline each time. So, the tuner doesn’t make the antenna work any better: it just takes some load off your transmitter. Answer

by pearsonartphoto

The key piece of information required to know if an Antenna Tuner is required is the SWR. If the SWR is higher than 1.5, you probably need an antenna tuner. If not, they it’s not really a requirement. The SWR changes based on frequency, so you need to keep that in mind as well. SWR can be measured by various meters, just keep your eyes opened for one. Okay, so what can cause the SWR to change? A lot of things really. The antenna needs to be at least a wavelength off of the ground to have optimal performance. It should be far away from metal objects. It might even change based off of local topology, and mineral content. These considerations are especially true for HF, which is why HF often has an antenna tuner. However, for VHF/UHF, the use of a tuner is rare, I certainly don’t use one. Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q)

Q: What is a “random wire antenna”? Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q) Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system? From everything I have heard, the resonance of the antenna (length, material) is what defines its performance on a given frequency. Is this only a minimalist emergency use concept, a fraction of a watt being better than no antenna at all? Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q) User: ron-j.-kd2eqs Answer

by wprecht–ab3ry

Yes, a random wire can be a practical antenna. Anything conductive can be loaded up. Somethings work better than others. But if you want to play around, there’s no reason the antenna has to be an “antenna”. There are, of course, some drawbacks: You must have a tuner. You might not get a match on every band you’d like to work. For efficiency, you need a counterpoise, an insulated wire that attaches to the ground of your tuner. Ideally, this is 1/4 wave long at the lowest band you’ll operate on. Note that this is not a radial, so it doesn’t have to be straight. The “antenna” starts at the back of your tuner (i.e., in the shack), so power levels must be low unless you like living in an RF fields and collecting RF burns. Answer

by n8wrl

It is amazing what can be used for antennas. On a lark, I tried what I read in a club newsletter once and connected a tuner to my downspout. I was able to work south americans on 10 meters! A random wire is just that - a random length of wire, possibly thrown over a tree limb or whatever gets it as high as possible fed with a tuner. You’re right - it won’t be resonant, and the tuner is just ‘making the radio think’ the antenna is resonant, but it could be very effective! The best part is experimenting - try it out! Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: What determines power handling capacity of an antenna?

Tags: antenna (Prev Q) (Next Q), power (Prev Q) (Next Q) I just bought a cheap 1/4-wavelength, 2m. mag-mount antenna. The package says it can handle 50 watts. I can think of three things that could limit the capacity: I 2 R losses in the connection to the feedpoint and in the antenna wire itself: increases with increasing current, produces gradual breakdown of materials; dielectric heating at the feedpoint: increases with increasing voltage and frequency, produces gradual breakdown of materials; dielectric breakdown at the feedpoint, happens suddenly when voltage is too large, produces immediate failure. Are these right? Are there others? Tags: antenna (Prev Q) (Next Q), power (Prev Q) (Next Q) User: pete-nu9w Answer

by phil-frost

I think you pretty much summarized limiting factors in the general case. I’d add that there can be dielectric losses or breakdown at the ends, as well as the feedpoint. Common antenna designs (quarter-wave verticals, center-fed half-wave dipoles) are fed at a lowimpedance node, and the ends are high-impedance nodes, so I’d expect dielectric breakdown (arcing) to be more likely at the ends than the feedpoint. At high power levels, the antenna ends can reach voltages high enough to cause arcing to nearby conductors (towers, trees, gutters) or corona discharge . Unlikely at your 50W example, however. I’d also consider RF exposure. Consider that this is is a VHF antenna, and that exposure limits are lower with increasing frequency. Also consider that this antenna isn’t installed in a fixed location, no one is going to test the RF exposure levels, and there’s nothing preventing anyone from getting close to the antenna. In fact, given that most people will stick them to cars, it’s not only possible, but likely that someone will be close. So, the manufacturer may specify a power limit due to regulatory or liability concerns. Answer

by wprecht–ab3ry

Cheap mag mounts, like many physically short antennas, have a coil in them to make up the correct electrical length. I am sure it’s made with the finest materials available. But it’s probably not. Even if it was, inexpensive means smaller gauge wire, cheaper connectors, etc. And so driving it at higher than it’s rated capacity is going cause it to heat up and the dielectric is going to breakdown and melt until you get a short. And of course, all the heat is power that isn’t leaving the antenna, so your efficiency is poor too. Tags: antenna (Prev Q) (Next Q), power (Prev Q) (Next Q)

Q: 1280 MHz propagation out of a mountain valley

Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q), uhf (Next Q) I live in a small valley, surrounded on three sides by 200-300 foot ridges. I’m trying to figure out where to place an antenna mast to receive 1280 MHz video from a long range aerial vehicle (20-30 mile radius). At this frequency, how important will line-of-sight transmission be in this situation? Will it be worth it to haul a 50-foot mast to the top of one of the ridges, and set it up there? (requires a solar panel / battery, and possibly a wireless relay to my shack). My current plan is a mast at my station; in the middle of the valley, which would get above the surrounding trees, but not above the ridges. Does it matter that aforementioned valley is populated with pine trees, which, as I understand it, will wreak havoc on the signal? What about a 433 MHz transmission from the valley floor to the aerial vehicle? P.S.: Please presume that there isn’t any HOA problem of physics, not legality.

/ building code in the area; this is a

Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q), uhf (Next Q) User: chris Answer

by amber

For the most part, propagation for VHF/UHF (1280 MHz is UHF) is line-of-sight because it doesn’t tend to get the benefit of ionospheric reflection like HF does. This will also apply to your mentioned 433 MHz transmission, which is in the UHF range. While there are occasionally atmospheric events that result in indirect UHF/VHF propagation (e.g. tropospheric ducting), they are not nearly as consistent as HF’s ability to DX. You’d almost certainly get much better reception (both ways) with an antenna located on the ridge where it can get a direct sight line to the aircraft. Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q), uhf (Next Q)

Q: How to determine antenna height for given HF frequency and coverage radius? Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q) I’m planning on setting up a low-HF antenna for near to mid-range contacts. In my particular case, ideally I would like to be able to cover a radius of approximately 1000-1200 km with good reliability, operating on 3.5 MHz and possibly supplanted by 7 MHz. (Using a combination of the two bands to achieve full coverage is perfectly acceptable.) At a minimum, I want to be able to cover something like a 600-700 km radius. I’m at approximately 58°N, locator JO68; this of course means that I need to take into consideration large seasonal variations in ionosphere illumination. Now, such coverage seems to me to be a nearly ideal fit for NVIS.

Given an antenna height above ground and operating frequency, how do I determine an approximate resultant coverage radius in the case of NVIS? Or alternatively, given an operating frequency and desired coverage radius, how do I determine how high above ground the antenna needs to be? I’m preferably looking for a (mathematical) answer that does not involve using antenna modeling software. For simplicity’s sake, let’s just assume a straight half-wave dipole at an even height above perfect ground. Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q) User: michael-kjörling Answer

by adam-davis

Near Vertical Incidence Skywave (NVIS) is already pretty well defined in both radius and antenna height by definition. The antenna achieves best performance no more than 1/4 wavelength above the ground, and typically reaches receivers 50km-650km (30-400 miles) away. It isn’t going to help you out much with receivers 1000-2000km away. Unfortunately there isn’t a single, simple, good calculation for antenna height vs transmission distance, which is why so many antenna modeling packages exist. You’ll get line of sight at close distances, which uses one equation. You can get groundwave propagation distances further out with another equation. Skywave and NVIS propagation distances will get you even further which each have their own calculations. An antenna modeling package takes into account all these various radiation modes, and can account for many other factors to bring you to a reasonable decision. You might not want to use one, but they were actually created to make this problem simpler to solve. Doing it by hand is more difficult, but can be rewarding if you want to learn more about propagation. The simplest answer is that the “ideal” height for an antenna at these frequencies is 1/2 wavelength - but even there “ideal” depends on whether you want optimum ground reflection. If you can’t get your 3.5MHz antenna 140 feet in the air, though, then “as high as you can” is the ideal height. Technically this is actually shifted up a little bit - the ideal height is 0.6 wavelengths above the ground, and every additional half wavelength thereafter (1.1wl, 1.6wl, etc). Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: How does a mag mount antenna achieve a ground plane? Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

I’ve been thinking for some time about magnet mount mobile antennas and wondering how they establish their ground plane. Consider that many mag mount antennas have some kind of protective coating on the magnet. Consider also that most cars have a coat of paint between the mag mount and the sheet metal. Both of these should result in some level of electrical isolation between the antenna feed shield and the sheet metal. I guess what I’m simply not clear on is how a mag mount antenna’s ground plane is connected electrically. Or is this accomplished through inductance? Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: peter-kb1avl Answer

by wprecht–ab3ry

There’s always a ground. Whether it’s what you intend it to be or not is another issue… A mag-mount antenna is grounded through capacitive coupling between that magnet and the metal it’s stuck to. At VHF/UHF frequencies, this effect is adequate for good results which explains the popularity of these mounts. Some folks advocate adding a wire instead of relying on the coupling effect, but in most cases, this has little or no effect. At HF frequencies, it’s a different story. The capacitive effect is not enough and thorough grounding of the vehicle is usually indicated. There are several good guides out on the internet, I suggest starting with K0BG’s excellent site on the ins and outs of mobile amateur radio oeprating. Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: Using MIMO in Amateur Radio? Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q) MIMO, Multiple Input, Multiple Output , is used widely in commercial data transmission. 802.11n and LTE devices use it to increase throughput, link reliability, and channel usage without increasing transmission power or using more bandwidth. While there are many examples of Amateur Radio enthusiasts building and used phased arrays, I haven’t found any examples of MIMO use in the Amateur Radio community. Are there good reasons MIMO isn’t used in Amateur Radio? Are there examples of Amateur Radio enthusiasts building and experimenting with MIMO systems? It seems that the increasing adoption of SDR and the continued interest in QRP would lead some down this path, but I haven’t found any information about it in the Amateur community. Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q) User: adam-davis Answer

by kawfey

There are a few radios that support diversity reception, but only to minimize effects of propagation rotation and multipath, not to increase data rates. This isn’t true MIMO. It’s more like SISO where the input is whichever one of two antennas has the strongest signal. Which brings up another point - data. There really isn’t that much data being used on ham radio at the moment. D-STAR is around, then Yaesu came out with a digital radio, and a lot of work is being done on things like Codec2 and FreeDV, but in general, it’s not all that prolific. However, MIMO in ham radio will still be reserved to things like HSMM and HamWan that actually have very large bandwidths. With that, the equipment is off-the-shelf. Some of it has MIMO capability, like 802.11N routers modified for use on amateur frequencies just like you mentioned in your post. It would be cool to have MIMO on lower bitrate and digital voice, but I don’t think the gains would be that great. I do undergrad research in statistical channel precoding using SDR MIMO transceivers on amateur bands, and man, is it cool…but people don’t have $40,000 to spend on a MIMO IQ vector generator/demodulator. I have yet to see a QRP MIMO homebrew rig, but that would be great! Tags: antenna (Prev Q) (Next Q), propagation (Prev Q) (Next Q)

Q: Buddipole model comparison Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q) Can anyone give me some insight into the different Buddipole models available? They look pretty similar to me except for the sizes. What would make you choose one over the other? Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: s3c Answer

by wprecht–ab3ry

I own some of Buddipole products. Buddipole is really a system rather than a product per say. It’s based around being able to create an effective antenna that is both portable and has flexibility for configuration. The real heart of the system is the VersaTee and the fact that all the parts for all the products use the same size threaded connector. All the pieces are made light for portability and the sizes are such that you can construct a variety of effective antennas based on your situation. With a more typical product, you have, say, a portable 10m dipole, period. With any of the three main Buddipole packages, you have the parts to make a number of types of antennas: vertical, dipole, even a yagi (with a few extra parts) on any of the ham bands

(except 160m). So really before answering the question of which one to buy, you have to identify how you are going to use it and what bands you plan to work. I really encourage you to download and read the free book Buddipole in the Field by NE1RD. It’s great. This guy took the Buddipole system through about every conceivable configuration and measured the results. Each section ends with a “cookbook” show the best recipe for each band. For my needs, I wanted to operate portable (SOTA) on 10m, 15m & 20m. So, using the information in the book, I bought the 8’ mast, the VersaTee, the Coax and the radial connectors. I didn’t need the coils or the tripod, so I saved a ton of money versus the deluxe package. For the radiator, I used the MFJ 17’ telescoping whip, which is full sized for 20m (and of course on 10, 12 and 15 by retracting some of it). I used the radial connectors to connect 4 elevated radials to the sides of the VersaTee, two off each side. These are supported at the ends by 2’ fiberglass rods (former 4’ driveway markers, [email protected]). Packed up for the trip, the whip sides into the hollow center of the mast and the 4 2’ rods are strapped to that making a nice compact bundle. Everything else is just wire and rope and 3 stakes all of which fits in a large ZipLock bag. Does it work? When I set everything up for 20m in my backyard, I got through to a station from Venezuala on the second call QRP from suburban Maryland and got a 59 even after telling him my setup. Answer

by dan-kd2ee

All of the buddipoles appear to be electrically the same antenna. The mini takes the two longest parts and puts a joint in the middle, so instead of having two 22” parts, you have four 11” parts, so it’s a little more portable. The deluxe is the same antenna, it just comes with some more options - a tripod, one of two heights of mast, and some spare parts. The regular buddipole doesn’t come with any of that, you’d need to mount it yourself or buy the other parts separately - but all their buddipole kits have the same antenna characteristics. Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: Is a vertical noisier than a dipole, and if so, why? Tags: antenna (Prev Q) (Next Q) I’ve had people tell me, anecdotally, that a vertical is noisier than a dipole. Is this true, and if so, why? If it is true: Is this additional noise, such that SNR is degraded, or is the vertical just more sensitive overall, making noise and signals equally louder? Is the noise particular to vertical monopoles? How would a vertical dipole be affected?

Tags: antenna (Prev Q) (Next Q) User: phil-frost Answer

by wprecht–ab3ry

I have read this too. I don’t have personal data to back this up, but the reasoning I have read stated that local RFI (like household appliances) tended to be vertically polarized and hence more able to induce noise onto a vertical antenna than a horizontal one. I’ll edit the answer when I find the references. Meanwhile there are a few really excellent papers on the use of ferrite to eliminate noise from all facets of your shack, I highly recommend them: Common Modes Chokes (W1HIS) Cost Effective Ferrite Chokes and Baluns (GM3SEK) EDIT: After some perusal of the literature, including the ARRL Antenna Handbook, I see nothing scientific to back up the anecdote. Which reminds me of a quote, from whom I forget: “the plural of anecdote is not data”. That said, I found 2 addition items of interest: 1. vertical antennas are omni-directional and therefore can pick all the noise there is to hear. 2. A reference that stated that RF noise had random angles of polarization (something that sounds more credible to me) and that RFI noise below VHF travels mostly by ground wave and interaction with the earth attenuates the horizontal component leaving only the vertical component. I don’t know if item 2 is any less of an anecdote than the question at hand, but that’s what I have found so far. Tags: antenna (Prev Q) (Next Q)

Q: Simple cheap foxhunting? Tags: antenna (Prev Q) (Next Q) I’m currently looking to do a foxhunt for a youth group, and need to keep it inexpensive and easy enough that it won’t be impossible for those new to foxhunting and ham radio, but difficult enough that it will still be rewarding. I’m a relatively new ham, so don’t have any of the required equipment. What is an inexpensive way to have a fox and two hunting setups? Can I buy three cheap HTs, fabricate two antennas, and use a ham operator for the fox to avoid the need for additional electronics automation? Is there a cheaper or better set of equipment? Note that the HTs would be under $100 [USD] total for 3 cheap dual band 4W units. Any reason this wouldn’t work, or would be frustrating for the hunters?

Tags: antenna (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

This should work fine. These cheap Chinese HTs don’t have many bells and whistles, but they are decent radios especially with non-stock antennas. For beginners I would start with some real simple scenarios and fairly open terrain. You don’t want a ton of multi-pathing scatter to confuse the new hunters. See my answer to your other questions for some methods. See the site

for lots of good information.

Tags: antenna (Prev Q) (Next Q)

Q: What is body blocking, and does it work with a stock HT on a foxhunt? Tags: antenna (Prev Q) (Next Q), ht (Prev Q) (Next Q) I’ve heard that you might not need a special directional antenna to participate in a foxhunt, that some people are able to use their body to help determine the direction of a signal. How does this work? More specifically, what is the process to do this, and why does it work? Does this only work on specific frequencies, or can this be used for 2M and 70cM dual band HTs with stock antennas? Is it tricky and requires practice, or could someone new to ham radio be taught it and effectively using it in a handful of minutes? Tags: antenna (Prev Q) (Next Q), ht (Prev Q) (Next Q) User: adam-davis Answer

by david-vk2vxk

Essentially this involves using your body as a barrier to fade the signals. Holding the HT close to you, and rotating until you get the weakest signal, then the source of that signal will be on the other side of you. In an answer to a different question , WPrecht - AB3RY quoted the following HandieTalkie Tricks tip from Joe Moell, KØOV’s Homing In website: When the signal is so strong that you can’t find the null, tune 5 or 10 KHz off frequency to put the signal into the skirts of the receiver’s IF passband. If your handheld is dual-band (144/440 MHz) and you are hunting on two meters, try tuning to the much weaker third harmonic of the signal in the 70 cm band while performing the “body shield.” Disconnecting the HT’s “rubber duck” antenna will knock down the

signal even more. Hearing the signal with antenna off is usually a “You are here!” indicator. Tags: antenna (Prev Q) (Next Q), ht (Prev Q) (Next Q)

Q: Is bending the tips of the antenna wires going to affect the effective length? Tags: antenna (Prev Q) (Next Q), diy (Next Q) I’m looking at designs for low cost DIY yagi antennas for a fox hunt, and pondering coat hanger wire and PVC piping. I’d like them to be built by the youth who will be doing the fox hunt, but that requires some safety considerations. If I plan to bend the tips of the coathanger wire back on themselves to avoid safety issues with the sharp ends, will I cut them to length prior to the bend, or should they be at length after the bend? The bend will be about a plier’s width of material, so maybe 5-8 mm, turned back 180 degrees, or nearly so. I don’t have equipment to test for antenna matching, so I can’t experiment on this, however these will be used for hunting, not transmitting, so I don’t expect it’s going to be critical. I’d like to get close, though. Tags: antenna (Prev Q) (Next Q), diy (Next Q) User: adam-davis Answer

by phil-frost

I would bend the tips back, twisting the free end around the standing end so you make a loop with good electrical contact between them. Measure from the base to the end of the loop for the purposes of calculating the length. The loop is almost entirely cosmetic and won’t affect the electrical length of the antenna much. If you were to make the loop bigger, you would have a capacitive hat, which would electrically lengthen the antenna. However, if you keep it small, and you fold it back and short the end back to the antenna, the capacitance added at the end will be negligible. Tags: antenna (Prev Q) (Next Q), diy (Next Q)

Q: What is the electrical shock risk of an antenna? Tags: antenna (Prev Q) (Next Q), safety (Prev Q) (Next Q) I’ve seen people refer to avoiding touching an antenna or bare transmission line that might be transmitting. What voltage potentials and currents are commonly found on typical ham radio antennas? Do both the voltage and current increase with increased transmitter power, or mainly one more than the other? What are the general safety measures one should take concerning antennas, specifically from the power going into the antenna purposefully? Antenna safety around powerlines and other power sources is a different question. Tags: antenna (Prev Q) (Next Q), safety (Prev Q) (Next Q)

User: adam-davis Answer

by on4aa

Most antennas have a standing wave along there length and are therefore effective impedance transformers. The feed impedance of a dipole might be of the order of 73Ω, at its ends, the impedance will be at least 2kΩ, if not higher. Solving for voltage at the antenna ends, we will have: −−−− P = VR ⇒ Vrms = √ P ⋅ R 2

Peak voltage is indeed √ 2 ⋅ Vrms , but the voltages at the ends of a dipole antenna are √2 balanced with respect to ground so: Vpeak = 2 Vrms , only half that value. Assuming a transmitter power of 1kW: −−−−−− −P⋅R −− 10 ⋅2⋅ / 10 √ 2 −−−− Vpeak = 2 √ P ⋅ R = √ 2 = √ = 10 = 103 = 1kV 2/ 3


6 2

If the antenna is loaded with a coil, the impedance will be transformed up to an even higher value. This is how a Tesla coil works. The resulting corona effect might be quite dramatic as shown in the picture below (1kW on 80m in short W4JRW dual-band dipole @ HB9DWU).


by ron-j.-kd2eqs

Touching a “live” (transmitting) antenna could impart a serious RF burn if the power level was high enough. This is different from the classic “electric shock” obtained by putting a

finger into a live wall socket. Radio frequencies heat tissue (non-ionizing radiation), proximity and contact with high RF fields will cause a RF burn. There is a risk of electrocution if the antenna is in contact with an overhead power line, although a well placed antenna should NOT be near any such hazards. Answer

by kd8tgr

RF burns aside (these often occur without physical contact), the voltage on the antenna can reach very high levels. There is a good discussion of this at . Paraphrasing the linked discussion, Ohm’s law applies, so if you’re dumping 50W into a 35 ohm load: −− P = I 2 R , so I = √ 50 35 = 1.195 V = IR = 1.195 ⋅ 35 = 41.83VRMS ⋅ √ 2 = 59.16VPEAK Toward the tip of the antenna, the impedence changes, so the voltage can be orders of magnitude higher (and the current lower). (Yes, I know V should be E, but old habits are hard to break. I also know that I’m using the RMS for a sine wave, but it’s a reasonable approximation.) Tags: antenna (Prev Q) (Next Q), safety (Prev Q) (Next Q)

Q: Is it safe to mount an active scanning antenna close to an hf antenna? Tags: antenna (Prev Q) (Next Q) I live in the centre of a seaside town in the UK. Because of lack of space I have a random wire antenna in the loft of a small house, and pick up a lot of noise on the top band Sunday morning CW ragchew. I am about twenty hilly miles from most of my friends and the noise overwhelms many of their signals. I have a Maplin “Super Scan Mk2” all band vertical antenna with a built in amplifier chip, which I have never used. I would like to try mounting the Maplin antenna on a pole a few feet above the roof to see if I can cut down the noise on reception. Normally I run 25 Watts on transmission. My rig is an Elecraft K2 with KPA100, which has a separate dedicated receive antenna socket, so no RF will be transmitted directly into the Maplin antenna. So, my question is: is the RF from my own transmission into the loft antenna likely to damage the nearby Maplin antenna internal amplifier chip during my tests? Tags: antenna (Prev Q) (Next Q) User: harry-weston Answer

by adam-davis

Generally speaking you should not place an active antenna near a transmitting antenna unless you know the active antenna can handle the power. Some can, but most, particularly generic wideband scanner antennas, aren’t intended to be used near transmitting antennas and the input stage may be easily damaged with a powerful transmission. Specifically discussing the antenna you mention, reports online indicate that this active antenna is sensitive to nearby transmitters: Unfortunately the Maplin Superscan Mk II is no longer available, or at least it wasn’t when I bought one of their last two in the country a few years ago. I’m now on my third (having blown the first two by transmitting too much power too close to them) and am treating it very carefully. (source


Other accounts suggest it’s otherwise a very good wide spectrum active scanner antenna. Were I in your shoes I’d look for other ways to resolve the noise problems and save the active antenna for more appropriate and safe uses. If you have details on the type of communications you’re trying to receive, and the type of noise you’re experiencing, ask another question and we may be able to help you solve your issue without putting your Super Scan Mk2 in harm’s way. Tags: antenna (Prev Q) (Next Q)

Q: Why do some antennas list modulation type alongside power rating? Tags: antenna (Prev Q) (Next Q), modes (Next Q), power (Prev Q) (Next Q) Looking at HF antennas I’ve noticed that occasionally I’ll see power ratings similar to “200W (SSB)”. Why would the modulation matter for an antenna’s power output rating, and in the absence of other information how does one properly derate such an antenna for other modes? Tags: antenna (Prev Q) (Next Q), modes (Next Q), power (Prev Q) (Next Q) User: adam-davis Answer

by michael-kjörling

It’s about transmission duty cycles. For example, FM has a very high duty cycle during transmission: the transmitter’s output power is constantly at 100% regardless of the amount of modulation. AM varies between 50% (carrier only) and 100% (full modulation). SSB varies with modulation between 0% and 100%. CW is like FM, 100% power output during transmission, but the actual periods of transmission are shorter for an overall much lower duty cycle than FM. PSK31 is somewhere in between FM and CW, with a high transmit power and moderate length

transmissions. And so on. What the manufacturer is telling you is mostly how much sustained power the antenna can tolerate. This is a matter more of heat buildup than e.g. the risk of arcing across components. What this means is of course also that without a specified duty cycle, the “SSB” figure is largely meaningless. If you have weak modulation, you can run the transmitter at a much higher power output setting than the 200W indicated because you really aren’t pushing very much power to the antenna. Conversely, if you have a very strong modulation, it’s possible that the antenna can’t take the power even though you have tuned the transmitter to a lower power output, because the actual power being fed to the antenna is higher than the manufacturer intended. If you know what duty cycle (in percent) the manufacturer’s specifications assumes, then you can work backwards to a safe continuous power. For example, if the maximum is 200W at 60% duty cycle, then the maximum safe continuous power is in the neighborhood of 60% * 200W = 120W. If the antenna is sold for amateur radio use we should also assume that the transmitter is not active 100% of the time, giving the antenna time to cool off. For a truly continuous transmission, you’d probably want to reduce the number to about one tenth, to simulate a 10% transmit 90% receive cycle. Once you know the safe continuous power, you can easily work your way backwards to any transmission mode. The other side of the coin is the maximum instantaneous power that the antenna can handle. This is easier, since we can fairly safely assume that the manufacturer wouldn’t say 200 W anything unless the antenna is capable of handling an instantaneous 200 W of RF. This is where issues such as arcing across coil windings, power handling capability at the feedpoint, etc., come in. Tags: antenna (Prev Q) (Next Q), modes (Next Q), power (Prev Q) (Next Q)

Q: Variable phase antenna Tags: antenna (Prev Q) (Next Q), diy (Prev Q) (Next Q) I’m thinking about phased antenna arrays, and am wondering if it’s possible to have three fixed position antennas, and vary the length of their individual feedlines to the common point through mechanical means. The best way to describe what I’m thinking is making a section of coax out of two telescoping sets of tubes, one outside shielding, and one inside conducting. I’d probably shoot for something other than telescoping antennas, and I’d be using a cheap DC drill with either woven thread or an acme screw to move the inner parts relative to the outer parts. I can leave one antenna connected to the common point via fixed length coax, and then connect the other two with these variable length coax devices in the feedline. It seems like it’s overly complicated, and that someone probably has come up with something better for switching a phased antenna array to point in any direction. Surely

someone has already built one (or perhaps it exists commercially and I just haven’t seen it yet) or people have considered it, but other solutions are better. What are other options I should consider? Tags: antenna (Prev Q) (Next Q), diy (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

I don’t know about mechanically steerable arrays, but there are several hams locally here that swear by a four-square electronically steerable arrays. The setup is typically done for 40m and is an array of four 1/4λ verticals arranged in a square 1/4λ apart. You run one feedline to a remote switch located in the center of the square and 4 identical length feedlines go from there to the individual antennas. You orient the square so the sides point in the directions you want to favor. A controller goes in the shack to steer the array. One company here in the US that makes an excellent controller is DXEngineering. The controller runs about 200USD, one plus the remote switch is about 600USD. The manual is available online so you can read up on it and see if it’s something you’re interested in. I don’t have a stake in them, but I have personally found their customer service and shipping speed to be excellent. If I had the room at this QTH I would definitely put up one of these. Alas, it will have to wait a few years… Tags: antenna (Prev Q) (Next Q), diy (Prev Q) (Next Q)

Q: Is there a simple, DIY, antenna suitable for HF receive only? Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q), diy (Prev Q) (Next Q) So the antenna I’m thinking about doing

might be* way too large for my property.

Is there another simple, cheap, DIY antenna I could try on my receiver? I know I’m going to want to hook it up and have a listen before the last solder joint has cooled. Ideally it would cover 160 m to 10 m reasonably well. The most complicated antenna I’ve built was a Gray Hoverman for UHF reception. It would be nice if it weren’t much more complex, but if it’s inexpensive and good enough I’m willing to do a bit of work for an antenna I’ll use a long time. I’m not interested in aiming right now, so an omnidirectional antenna would be best. I do have a 25’ attic I can use if needed. *Is almost certainly… Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q), diy (Prev Q) (Next Q) User: adam-davis Answer

by phil-frost

Receive antennas are the easiest thing ever. You just need two things: 1. something that conducts electricity 2. another thing that conducts electricity Attach one to the center contact on a BNC connector. Connect another to the shield. Boom, done. If you can’t find two things, then one can be the Earth. Alternately, you can use two ends of one thing that encircles something that permits magnetic fields (like, air). Until you are approaching a significant fraction of a wavelength (like, 1/4 wavelength), then making either thing bigger will get you more signal. However, once you have enough signal that you are well above your receiver’s noise floor, more signal won’t make you receive any better: it will just give you louder noise. I’d say, however much space you have, make it that big. Don’t worry about tuning, or impedance matching. This also will increase the fraction of the energy received by your antenna coupled to the receiver, but again, once you have enough to overcome the receiver’s noise, more is of absolutely no help. See What is the relationship between SWR and receive performance? Don’t worry about polarization. At HF most of your signals will arrive via the ionosphere which is constantly swirling and changing the polarization of received signals. Whatever polarization you pick, it will be the wrong one in 30 seconds, so don’t worry about it. If you really must worry about something, worry about getting your antenna away from noise sources. Your house, being full of all varieties of noisy digital electronics, is very noisy. If you can get an antenna away from these things, that’s good. You must also take care to avoid making the feedline part of the antenna. See Using a balun with a resonant dipole Although that question asks about resonant dipoles, the answers apply to any type of antenna. Answer

by wprecht–ab3ry

There is nothing simpler than a random length wire. It doesn’t have to be strung up or even straight, though, obviously, those would improve it’s performance. Of course the ironic thing about a random length wire antenna is that the most effective lengths aren’t actually random. They work best when the antenna is at least a quarter wavelength at the lowest operating frequency, 65’ for 80m, for instance. To maximize the effectiveness, and have something useful down the line, you could build a small tuner. An L-network random wire tuner is probably the simplest matching network in existence, designs about on the net. Like this one: How to Build a Cheap Antenna Tuner or this one: SWL Receiving Antenna Experiments . Tags: antenna (Prev Q) (Next Q), hf (Prev Q) (Next Q), diy (Prev Q) (Next Q)

Q: What makes a 5/8 wavelength vertical desirable?

Tags: antenna (Prev Q) (Next Q) An ordinary 1/4 wavelength vertical is smaller and resonant without any loading coil or matching network. What’s the advantage to a 5/8 wavelength vertical? Why 5/8 in particular, and not something longer or shorter? Tags: antenna (Prev Q) (Next Q) User: phil-frost Answer

by wprecht–ab3ry

Indeed, why? A 5/8λ isn’t resonant where a 1/4λ or 1/2λ would be. The reason is the radiation pattern. The pattern for a 1/4λ monopole is essentially a doughnut, tasty and a pretty good pattern especially for a VHF antenna. Extending the antenna changes the current distribution. This flattens out the pattern removing power from the useless (for VHF purposes) vertical dimension and giving more horizontal gain and at a lower angle. See the following illustration from the late great L. Cebik:

Depending on the source, they will quote anywhere from 1.2dB to 3.5dB gain over the 1/2λ design. There has also been some discussion that in some areas (urban and mountainous terrain) the lower angle of radiation is a detriment and a standard 1/4λ or 1/2λ antenna is to be favored. I don’t know. I guess they are pretty cheap, if this is a concern you can buy one mount and two and antenna, compare them for a bit and return the loser. So, why 5/8λ? Why not long longer? After all more gain is better right? Well, inspecting the figure above you will notice the appearance of high angle lobes. As you lengthen the antenna past 5/8λ these lobes become more pronounced and break up the pattern in undesirable ways. Making it shorter maintains a good pattern, but the gain is less. So, 5/8λ is about optimal for this style of antenna. Tags: antenna (Prev Q) (Next Q)

Q: If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is

more efficient? Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) If there are two antennas of 50 Ω and 377 Ω (same as the intrinsic impedance of air) impedance with 0 Ω ohmic resistance, and they are exactly matched with their transmission line, then which antenna is more effective in terms of radiating R.F. power into space? That is, if both antennas have VSWR = 1:1, then which one is more efficient? Note: that the term ‘efficiency’ in above, does not mean the definition of antennaefficiency. I know that antenna-efficiency is 100%, since there are ZERO ohmic loss and ∞ return-loss. So, from “efficient”, I mean the effectiveness of the antenna in radiating energy in space. Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) User: kaka Answer

by phil-frost

With the information you’ve provided, there is no way to tell. Feedpoint impedance and VSWR have no relationship to antenna efficiency. See What is the relationship between SWR and receive performance? The feedpoint impedance also has no relationship to antenna efficiency. A “50Ω antenna” means the impedance at the feedpoint is 50Ω. The impedance at other points is probably something very different. In a dipole, for example, the impedance is about 72Ω at the feedpoint, and very much higher at the ends. This is why current is at a maximum at the feedpoint (low impedance), and at a minimum at the ends (high impedance). Is there an advantage to an antenna with a feedpoint impedance equal to the impedance of free space? No. An antenna of any design transforms between the impedance of free space to its feedpoint impedance. An antenna can be designed to work at any feedpoint impedance. The losses come from things like resistance in the antenna wire and coils, and dielectric losses in tuning capacitors. To the extent that you don’t have these things, an antenna can be efficient. A dipole, vertical, loop, or any other kind of antenna constructed from ideal materials is already 100% efficient. This can easily be seen by considering the law of conservation of energy. If your antenna isn’t getting hot, yet you are putting 100W of power into it, only two things can happen to that energy. It can be be: 1. stored in reactance of the antenna 2. radiated away If the antenna has a purely resistive impedance, then there is no reactance to be storing energy, so it must be radiating away. The feedpoint impedance is irrelevant. Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q)

Q: What are some good options for covert dual band vehicle antennas? Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q) Would like to have a 50W mobile in my SUV, but I’m not allowed to have a big whip on the outside. What 2m/70cm dual band antennas are available that don’t say, “Ham Radio Operator”? Are there three band antennas that replace the radio antenna? I’d probably be allowed a short, small antenna like the fin satellite antennas popular with the satellite radio crowd, are there any dual band antennas in a similar form factor? Are there good places inside the vehicle to hide an antenna? I’ve heard some people are able to place them inside the plastic bumper, but given the rest of the car is metal I’m not aware of any other discreet locations. Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

Depending on how your terrestrial radio antenna is mounted, it may be possible to remove it and mount a small dual band antenna there and likely no one would notice. I tried that on my truck, but that area where the antenna mounts is on the plastic frame in front of the windshield, not down on the fender. There was no way to really get in there and swap the bases out. I also removed my terrestrial radio antenna anyway (just unscrewed the element) as I have satellite radio and that was unnecessary. If you have that situation, there is always the option of drilling and installing a mount there on the fender. Other than that, all your other (effective) antenna options are going to be somewhat less discreet. For an SUV, a jam mount or lip mount on the rear door/hatch would work, a 1/4 λ antenna is only going to be about 20” long for 2m. Even shorter for 70cm. Black mount and black antenna and it should blend in well. A useful dual or tri-band antenna is going to be 30”+. At that point it’s going to be hard to call it anything other than what it is. Depending on who you are hiding this from, another option is mounting on the roof rack, if you have one. There are these motorized mounts designed for people that park in garages that lay the antenna down for parking. You could mount that and only raise the antenna when you are on the road and operating. There are no good areas inside the vehicle, the body makes a moderately effective Faraday cage and the losses are brutal. I can’t imagine anything hidden in a plastic bumper being very effective since VHF is pretty much line of sight and the mass of the vehicle is always going to block out 1/2 the sky.

A final option is a small mag mount or a window mount that you put up only when operating and take off and toss in the back when you aren’t operating. Nothing permanent or too obvious. Again, this all depends on whom you are hiding from. Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: Height and feedline loss tradeoff for VHF Tags: antenna (Prev Q) (Next Q), coaxial-cable (Next Q) Currently my 2m antenna is about 3m above the ground inside, my HF antenna is connected to 30m (2db loss) coax and is about 12m up. Since the loss for 2m is a lot more when traveling down such a long piece of coax will moving my 2m antenna to the same mast as the HF antenna be worth the gain in height? Tags: antenna (Prev Q) (Next Q), coaxial-cable (Next Q) User: s3c Answer

by benswayne

I’m not a feed line guru, but I’m not sure your question as its worded now has an academicly “correct” answer anyway as it’s a matter of owner preference and local conditions. You should clarify what you want from your VHF setup. If you can already effectively work all your local repeaters and are not concerned with simplex coverage, then maybe it won’t be worth relocating your VHF antenna for you. If you are concerned about simplex coverage for emergency use when repeaters could be down, then the height improvement may be worth any potential feed line loss to you. If your living conditions or significant other require you to move the antenna for space/placement reasons, the top of the tower may be nice and out of the way. You will need to weigh these benefits and costs against your desired performance. Of course if you are running inexpensive feed line with your VHF antenna indoors, moving it outside with good quality feed line may not cost you anything more than you are already losing with the antenna indoors! So its just a matter of cash and time to mount it right. EDIT After comments: Taking into account your clarification in the comments above, I would say getting the antenna outdoors and replacing the “car kit” feed line with quality low loss feed line will likely give you an all around better setup. ARRL seems to recommend Belden 9913 or LMR-400 . “For base stations in particular, always buy the lowest-loss coax you can afford.” - from that same ARRL page. I’ve seen more than a few people put a VHF vertical above the apex of a dipole on a tower. But hopefully someone more knowledgeable than I can advise on a recommended minimum separation distance. If you can keep the vertical a few feet above the dipole that

will help reduce any interaction between them. Whatever separation distance you can achieve, I’d be pretty confident your setup will improve getting your antenna outside with better feedline. Answer

by phil-frost

Usually, higher is better, assuming you are using coax that isn’t exceptionally lossy. At VHF, this will be something other than the cheapest coax you can buy. Unfortunately, that’s the most accurate answer you can get here, because the benefit of additional height depends on a lot of things about your environment that we don’t know. Are there buildings in the way? Trees? What are ground conditions like around your location? What’s the height of the other antenna? The best height will be the one where coax loss + path loss are at a minimum. Calculating the coax loss is easy: read the datasheet. Calculating path loss not feasible, but you can measure it. Put your antenna on a piece of coax long enough to reach to your highest height considered. Mount the antenna down low. Go far away. Make a test transmission. Measure the received signal strength. Now move the antenna up higher and repeat. Now you know what you stand to gain by putting the antenna higher. Compare that to what you will lose, calculated from the coax specifications, and you will know if higher is better. Answer

by kd5qln

Some possible solutions would be: 1. Get better feedline, like LMR400 2. Get an LNA , this is a special amplifier that sits between your antenna and feedline and is powered by a supply at the other end of the feedline. 3. Transverter . A transverter will take for instance a 10m signal and convert it to 6m and vice-versa. You see these a lot in the GHz spectrum, as installing waveguide or LMR1200 is not practical. Tags: antenna (Prev Q) (Next Q), coaxial-cable (Next Q)

Q: What antenna on a BaoFeng UV-5R Pro will give me better reception? Tags: antenna (Prev Q) (Next Q), uhf (Prev Q) (Next Q) I am happy with my BaoFeng UV-5R Pro but the local UHV VHF repeater and simplex reception is terrible, even for contacts less than 50 kilometers. I assume that it’s because the rubber-ducky antenna on it is terrible. What can I replace it with that is readily available commercially, costs less than $100 US, will give me a better handheld reception experience, and still maintain excellent portability (for my case, let’s say that means less than 2.5 pounds antenna weight, less than 3 feet tall)? I don’t know much about dBi gain, but I have seen antennas claiming to be “144Mhz 2.15dBi 430Mhz 3.0dBi”, I’m still learning so I don’t know how to interpret that information. Tags: antenna (Prev Q) (Next Q), uhf (Prev Q) (Next Q) User: warren—ve3wpx Answer

by adam-davis

Every time I purchase a cheap HT such as the Baofeng you mention I also spend another $10 or so on an antenna, as the stock antenna is noticeably worse than even an inexpensive antenna like the Nagoya NA-771 . There are still better antennas than this, but there are always tradeoffs. The stock antenna is one third to half the length of the NA-771, which is useful in certain situations. There are vastly better, but more expensive, antennas that mount on and off the radio. What you need will depend largely on what you’re going to use the radio for. Given that you’ve chosen an inexpensive, low power (even for handheld) radio, though, I suspect you’re really looking to improve things as much as possible while still retaining the portability and use as a handheld, without a lot of cost. So the above antenna is my current recommendation in this situation. Answer

by phil-frost

The antenna included with the BaoFeng is notably bad, even for a rubber duck. To answer your question of what would be better: anything would be better. You’d have to switch to a dummy load to do worse. Whatever antenna you do select, it need not be anything specific to your radio. Any antenna suitable for whatever bands you wish to operate will be fine. The only gotcha with BaoFeng radios is they have a male SMA connector on the radio where every other radio made has a female connector. They are popular enough now you can find antennas with this connector, or you can find adapters. Quality aside, rubber duck antennas trade size for efficiency. It generally true that the smaller an antenna is made, the less efficient it is. A full-size whip will be a quarter

wavelength, so approximately half a meter long for the 2 meter band. There are designs with degrees of shortening anywhere between that and a rubber duck, so get the longest one that isn’t “too big” for your preferences to maximize efficiency. Answer

by andrew-spiehler-kg5abv

Most HT antennas can be purchased for far less than $100. You can buy a 1/2 wave VHF Nagoya antenna from most online sources for approximately $10. Better brands will cost a little more. The dBi value is the forward gain of the antenna when compared to a theoretical isotropic antenna (hence the i in dBi) that radiates all its power evenly in all directions. To be of any use in your case, you’d also need to know the dBi gain of the rubber duck antenna, but, as was stated in another answer, rubber duck antennas have traded off performance for size so any whip antenna is almost guaranteed to perform better. Tags: antenna (Prev Q) (Next Q), uhf (Prev Q) (Next Q)

Q: What is the average fade margin required for proper operation at 2.4 GHz? Tags: antenna (Prev Q) (Next Q), amplifier (Next Q) I have two radios. Sensitivity is -84 dBm and transmitting EIRP is +30 dBm. How much distance should I expect? I want it to be somewhere near about 2-3 km. Is it possible? Tags: antenna (Prev Q) (Next Q), amplifier (Next Q) User: user40713 Answer

by phil-frost

Your question can be answered by the Friis transmission equation is: λ Pr = Pt + 20 log10 ( ) 4πR

. One way to write it

Where: Pr is the received power (in dBm) Pt is the transmitted power λ is the wavelength R is the distance between the antennas, in the same units as wavelength Wavelength at 2.4GHz is about 0.125m. With your numbers of 30dBm, and a maximum distance of 3km, the equation becomes:


= 30 dBm + 20

10 (

0.125 m


0.125 m ) 4π ⋅ 3000 m = 30 dBm − 109.6 dBm = −79.59 dBm

Pr = 30 dBm + 20 log10 (

This is about 4dB above your specified minimum of -84dBm, so it’s theoretically possible, but only barely. The Friis equation calculates received power for ideal propagation in free space between isotropic antennas. Your receive antenna probably has some gain which gives you some additional margin. A resonant dipole has theoretically a 1.76 dBi gain, which adds to the number calculated above. Of course if you have a more directional antenna you get even better improvements. However, you also aren’t propagating through free space. You can approach this with a very good path: antennas on towers, clear line of sight, and so on. You must also consider the Frensel zone around the path also. If all of these conditions are very good, your losses compared to free space will be small or negligible. If not, you will need additional antenna gain or transmit power to make your link work. Tags: antenna (Prev Q) (Next Q), amplifier (Next Q)

Q: If I install a G5RV in my attic how could I be certain there are not harmful levels of RF in the shack, or my kids bedroom? Tags: antenna (Prev Q) (Next Q), safety (Prev Q) (Next Q) I assume that anyone who has a G5RV or G5RV junior in their attic has done so with ceramic spacers, and has zigzag or dog-leg installations, or otherwise has contorted the antenna to fit up there. My worry is how can I satisfy my own and my XYL (wife)‘s concerns about RF in our house, especially in the bedrooms immediately below the attic, where all of us sleep? What do I need to know, and what do I need to measure to know if any harmful RF levels would exist in the area 12 feet below the attic? Assuming that other questions here cover using radios or Oscilliscopes to measure and observe decreases in RF in the shack, how can I establish reasonably easily that levels not more than 1/10th of the level that could cause harm, are present in my house? For example, if high levels can cause GFCI breakers in my outlets to trip, how high would such levels be, compared to the levels that could cause damage to people? Is there any way to know? Tags: antenna (Prev Q) (Next Q), safety (Prev Q) (Next Q) User: warren—ve3wpx Answer

by phil-frost

If you want to be certain, you will need calibrated electric and magnetic field probes and a spectrum analyzer. If you had that equipment, I doubt you would ask this question, so let’s assume you don’t have it, and you don’t care to drop thousands of dollars to get it. How can you be pretty sure that exposure is safe, without expensive test equipment? First we have to define safe. Since this forum is about Amateur Radio, and not medical research, let’s use the FCC’s definition of safe. The FCC has determined that amateur operators need not give any special consideration to RF safety if the transmitter power is below a certain level. At these relatively low transmitter powers, it’s just really hard to encounter a dangerous field, no matter how close you get. The ARRL gives a full table , but all bands 15m and below are good at 100W PEP or less (limits are even higher on lower bands). The limit for 12m is 75W, and 10m is 50W PEP. That covers the usual operating range for a G5RV. If you exceed those limits, you may very will still be safe, but you have to do some analysis. Here’s a simple way to do it: the maximum power density for 3MHz to 30MHz is 180mW per square centimeter, divided by the frequency in MHz squared. We can estimate the power density by making some simplifying assumptions. If we leave a big margin, we can still be pretty sure we are within safe limits despite our gross simplifications. First, let’s assume that power is radiated equally along the antenna’s length, and that you are close enough that we should consider it as a line source, not a point source. If you put 100W into it, then for any cylinder centered on that antenna, there is 100W passing through it. The half-size G5RV, being smaller, will have higher power density. It’s 15.5m long. Let’s say you are 3m away from it, and you are feeding it with 100W. The area of a cylinder (without the ends) 15.5m in length and 3m in radius is: 2π ⋅ 3m ⋅ 15.5m = 292m2 Your 100W of transmitter power is spread over this cylinder, so the power density is: 100 W 292 m2

1m 1 m 1000mW = 0.0342mW/cm 100cm 100cm 1 W

Let’s call the top end of 10m an even 30MHz. The maximum safe power density is: 180 = 0.2mW/ cm2 2 30 So, you are 7.6dB below the FCC limit for uncontrolled exposure. I’d call it safe. Remember that this is a gross simplification. Factors that make our estimation less safe include: power isn’t actually radiated equally all over the antenna. There will be hot spots, and cold spots. with the antenna in your attic, you aren’t even in the far field of the antenna. Calculating the actual fields is really hard. ground reflections, and also any wiring in your house, may reflect, distort, or focus

the field, making more hot spots. Factors that provide additional safety margin to our estimate include: the antenna doesn’t radiate like the worst-case cylinder: some power goes towards the sides also. exposure limits are higher for lower frequencies (at 7 MHz: 3.6 milliwatt per square centimeter). SSB power is usually measured in PEP, while exposure limits are set by average power over 30 minutes. SSB has a duty cycle around 20%. Regardless of the mode you use, you probably don’t transmit all the time, further reducing duty cycle. Answer

by imabug

The ARRL RF Exposure page has a lot of useful resources. It has links to a number of articles and external websites that provide some good info. If you happen to have a copy of the ARRL Handbook, the Safety chapter has a section that covers RF safety. Between 1.34-30MHz, the FCC maximum permissible exposure (uncontrolled exposures/general population) for power density is 180/f2 mW/cm2 and 0.2 mW/cm2 between 30-300 MHz, where f is the frequency in MHz. As for measuring the field strengths, it’s probably not something you’ll be able to do yourself without some specialized equipment. There are companies that can do this for you, but if you’re not running more than 100 W, it’s probably not worth the expense. This RF safety calculator looks like it would be useful to see how close you might be to any limits. Tags: antenna (Prev Q) (Next Q), safety (Prev Q) (Next Q)

Q: Antenna RX vs. TX Tags: antenna (Prev Q) (Next Q) If I only want to receive radio signals and not transmit, are there any differences in the way I design the antenna I need to use, or is it the same either way? I was going to pick up a Realtek RTL2832U and use it as an SDR, but it has an antenna that I would like to improve. (Approx range: 25MHz-1700MHz) Tags: antenna (Prev Q) (Next Q) User: jason-petrilla Answer

by kevin-reid-ag6yo

Most of the issues are already covered in this previous answer by Phil Frost to “Is there a simple, DIY, antenna suitable for HF receive only?”:

Receive antennas are the easiest thing ever. You just need two things: 1. something that conducts electricity 2. another thing that conducts electricity … Don’t worry about tuning, or impedance matching. This also will increase the fraction of the energy received by your antenna coupled to the receiver, but again, once you have enough to overcome the receiver’s noise, more is of absolutely no help. … If you really must worry about something, worry about getting your antenna away from noise sources. … As covered there, most characteristics of the antenna don’t matter if you are not transmitting. However, if you are interested in the VHF/UHF (rather than HF) frequencies which those receivers cover, there are a couple more concerns. 1. Polarization matters, because it is not randomized by the ionosphere. You will want your antenna to be vertically or horizontally polarized depending on what signals you want to receive. In the amateur radio bands, most VHF/UHF signals are vertically polarized. 2. Location matters. At these frequencies signals are much closer to propagating like light — you want a clear path from the transmitter to your antenna, if possible. For strong transmitters like FM broadcast stations and amateur repeaters, this is less of an issue. 3. Finally — this is equally applicable to HF but more practical at higher frequencies — if you are seeking to receive weak signals, it is helpful to have a directional antenna pointed at the source. The most common amateur uses for directional antennas at VHF are satellite communications and direction-finding. So, get a piece of wire of roughly the right length for the band you think you’ll be most interested in (again: doesn’t matter much), mount it vertically as high in the air as you feel like arranging, hook it up to the center contact of your receiver’s antenna port, and there you go. Or if you want to buy something premade, buy a “scanner” antenna, because those are intended for receive-only use and wide bandwidth. Tags: antenna (Prev Q) (Next Q)

Q: Is a VHF antenna on a vehicle’s body a bad idea? Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q) For context, I’m brand new, with nothing but an HT & 19” dual band (2m/70cm) whip on

it. While I’ll likely go with a magnetically mounted vertical antenna, I’ve been thinking of other more covert options. For instance, could I do a 1/2 wave dipole mounted along the roof? A 2m dipole is just a little over 3 feet and would easily fit along the edge or middle. I’d need to insulate it, I’m sure, but would that work or be worth the effort? What about vertically along a door frame? The bumper is already insulated. Even if the car body reflects the RF in one direction, could I then combine one in the front and one in the back bumper? Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: conan Answer

by phil-frost

A horizontal VHF dipole above a (presumably metallic) car roof is not a good idea. Because the car roof is relatively large relative to wavelength, and is a good conductor, you will get a lot of RF current in it through capacitive and inductive coupling. This isn’t a bad thing in itself, but because the geometry of your car isn’t designed as an antenna, the result will be difficult to predict and probably not very good. Here’s one problem: if we think of the car roof as an infinite conductive plane (just a rough approximation of reality), it will make an image antenna . If your dipole is very close to the roof, then this image antenna will cancel most of your antenna’s radiation. As you get it higher you will get less cancellation, but most of the radiation will be up, towards the sky. When you get it to half a wavelength high, then this is no longer a problem , but then why not just use a mag-mount vertical, which is just as tall? For a vertical, the ground plane and resulting image antenna is a good thing. Of course your car isn’t an infinite plane. RF currents will flow all over the car body, and probably you will get a lot of radiation from slot antennas formed by seams in the car body. The trouble is we don’t know what they will be. They probably won’t offer a good match to your 50Ω coax. Also, the polarization could be anything. By convention, FM on VHF uses vertical polarization. If you happen to radiate with horizontal radiation, you will only be heard by most people through paths that rotate your polarization. In practice, this means a loss on the order of 30dB. Radiation from your car body probably won’t be entirely horizontal, so it may not be so bad, but most likely, it won’t be so good. Another issue may be the electronics in your car. With the dipole laying against the car body (anywhere), the coupling between the dipole and the car body is so good you might as well have soldered the feedline directly to the car body and skipped the dipole. It’s obvious then how much RF current is in the car body, and all the wiring attached to it. Automotive electronics are usually pretty robustly engineered, but I’m not sure I’d trust them to work with an RF transmitter hooked up to them. Tags: antenna (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: Share antenna between receiver and transceiver? Tags: antenna (Prev Q) (Next Q), receiver (Next Q) I recently put up a fan dipole for 80/40/20/10. I’m looking for a way to share this antenna with a receive-only SDR and my shack transceiver. Obviously I can just switch this antenna between the two manually, but I was hoping there was a way to have both hooked up at the same time without transmitting into my SDR. Is there a practical, cost effective way to accomplish this? It would be great to have a waterfall display of the entire band while I’m going at it. Tags: antenna (Prev Q) (Next Q), receiver (Next Q) User: s3c Answer

by pete-nu9w

Back in the olden days, before transceivers took over, the transmitter and receiver were separate units, and the receiver had to be protected from the transmitter. The solution then, as now, is an electronic T/R switch. One approach is an RF sensor that triggers a relay; the MFJ-1708 is one example. A more sophisticated approach uses an active element to isolate the receiver. Used to be a vacuum tube, and if you do a Google search you’ll find lots of DIY TR switch projects for vintage radio fans. Answer

by wprecht–ab3ry

Without serious isolation, you will smoke the SDR the first time you transmit. Typical (i.e., cheap) coax switches suck at isolation. If you are lucky it’ll be 30 dB down. That’s still enough to smoke the SDR easily unless you are QRP. The only way that comes to mind is to make a relay that drops out the SDR when you key up your rig. Most rigs have a signal line to key an amp up, you can use this signal to drive the relay. Basically the inverse of the amp keying circuit. Tags: antenna (Prev Q) (Next Q), receiver (Next Q)

Q: How does a “chip antenna” work? Tags: antenna (Prev Q) (Next Q) How does a tiny surface-mount “chip antenna” for the 2.x thru 5.x GHz frequency bands work? What allows such a tiny item to radiate or receive RF with some amount of efficiency? What allows a chip antenna’s radiation pattern to be (somewhat?) nondirectional compared to a wire antenna? Tags: antenna (Prev Q) (Next Q) User: hotpaw2


by oh2fxn

The chip antennas use some material, usually ceramic, that has high permittivity and low losses. In a medium having high permittivity, the wavelength is shorter than in the free space. This way the antenna “sees” the structure that is comparable in the size to the wavelength in the medium, while being very small compared to the free space wavelength. While receiving, the antenna efficiency is not very crucial parameter since less efficient antenna receive less signal but also less noise from the environment. Thus the signal to noise ratio is the same at the output of the antenna. See the related questions: What is the relationship between SWR and receive performance? and If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is more efficient? Generally, small antennas tend to be less directive: for example, large dishes have higher gain than Yagis that, in turn, have higher gain than dipoles. Based on empirical googling, the chip antenna manufacturers seem to promise gains approximately in the range of 0…3 dBi. However, with high permittivity substrate you can achieve large gains as well: Tags: antenna (Prev Q) (Next Q)

Q: Why does ice on a wire dipole affect the SWR? Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) We just had snow and ice overnight and my wire dipole was coated in ice. Why does the ice covering negatively affect the SWR of the antenna? Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q) User: ron-j.-kd2eqs Answer

by phil-frost

A heavy coating of ice or snow is likely to short the feedpoint of the antenna. Compare:

simulate this circuit

– Schematic created using CircuitLab

Even if the wires and feedpoint are protected by insulation and the ice isn’t directly touching, a thick coating of ice will make a tube around the wires, and the resulting capacitive coupling is a low impedance at RF. (ANT3) Snow or ice isn’t a great conductor, but it’s a much better conductor than the air or PTFE insulator that was between the halves of the antenna. Clearly the antenna impedance, and thus the SWR, will be affected. The change in temperature, dielectric constant, and other things mentioned in other answers do affect the antenna impedance, but not to a very significant degree. I’d wager that 80% of the times you sit down in the morning after a storm to find the SWR is all messed up, it’s because there’s water in the feedpoint. The other 20% of the time, it’s because the antenna is sagging into a tree or the ground or broken from the additional weight. Tags: antenna (Prev Q) (Next Q), impedance (Prev Q) (Next Q)

Q: What kind of antenna has a spiral connected to a reflector like this picture? Tags: antenna (Prev Q) (Next Q)

The description on the antenna says it is used for satellite communication, but it was taken in 1984. Is this an antenna style that is still in use? What is it called? What kind of gain should be expected? Is this a style used primarily or only for communications in space? It appears to be a Yagi style antenna strapped to a parabolic, but I’ve never seen anything like this, so that conclusion may be completely wrong. Any information or links would be awesome. Tags: antenna (Prev Q) (Next Q) User: jason-petrilla Answer

by juancho

This is a helical antenna

(Wikipedia link


Configured in axial mode, these are commonly used in microwave satellite communications (below a few GHz) where you need high gain and circular polarization. The circular metal part behind acts as a reflector element. It is not only used for space communications. You find similar antennas for directional data links (using WiFi or similar modes). In normal mode configuration, axial antennas act as a short dipole. Its the wire spring you find inside flexible antennas in portable (handheld) transceivers. Answer

by paul

I’ve built a helical antenna for 430-440MHz receive from mostly ordinary household

items. It was sufficient to receive the FO-29 downlink. The dimensions of the helix are determined by the center frequency. I think the helix you posted is larger in circumference than mine, and thus would have a lower center frequency.

I believe gain is a bit lower than a yagi of the same length, but the helix is circularly polarized and so spin fading in satellite service is not an issue as it would be if a yagi or quad were used. I chose a center frequency of 436MHz which gives wavelength of 68.8cm. From my notes I see that the design choices were 1.1 wavelengths for the helix circumference (75.7cm), and turn spacing to circumference ratio of ~0.23 (turn spacing 17.5cm). A generalization of Pythagoras’ theorem can be used to give the wire length per helix turn as −−−−−−−−−− √ 75.72 + 17.52 = 77.7cm . I used white solid insulated 12 gauge copper wire marked every 1/3 of a turn with a bit of black wire tape to assist in attaching to the 3 supports. These choices were influenced by various articles I had read on-line, but unfortunately I did not keep these links and the design notes are on notebook paper. For the reflector you need a circular metal plate, such as a pizza pan and to support the wire helix of radius ~12cm I used three bamboo poles arranged in an equilateral triangle with ~21cm side length. Turn spacing is about ~17.5cm. Bamboo is an irregular material. It is not straight, although you can find “approximately

straight” pieces. The bandwidth of the helix is wide and the design fairly tolerant of error, allowing for somewhat imprecise construction. To increase the strength and rigidity of the support it is necessary to form some triangles with additional bamboo pieces. It becomes almost like making bamboo triangular tower. A helix antenna does not present 50 ohms without a tuning or matching section. I remember reading somewhere that other builders had successfully used 1” copper strap, 1/4 wavelength, at an adjustable (but close) height above the reflector. Create a few threaded holes in the reflector using a tap and then you can use plastic bolts and scrap plastic (like a consumer discount card) to hold the copper strap at an adjustable height. See also the QRZ page for KI6CQ Tags: antenna (Prev Q) (Next Q)

Q: How to stack circular polarised antennas Tags: antenna (Prev Q) (Next Q) I’m interested in stacking a pair of circularly polarized “crosshair” antennas. Do I construct such as both antennas are in phase with one another then match the two signals in phase via the coax line, i.e. equal length, or should I rotate one by say 180 degrees then use the coax to provide a phase shift? I’m new to RF but pretty eager to learn. Tags: antenna (Prev Q) (Next Q) User: ben Answer

by phil-frost

The important thing is that the antennas are in phase. That is, at the instant the electric field is pointing up on one antenna, it’s pointing up on the other antenna. Otherwise, they won’t add constructively. In the worst case, they are 180 degrees out of phase and they cancel. Keeping the antennas in phase can be accomplished any number of ways. If the coax length to each antenna is equal, the phase shift introduced by the feedline will be equal, so the antennas will be in phase as long as you don’t rotate either one. If you were to rotate one to be ahead 180 degrees in phase, you could compensate by adding an extra half-wavelength (at the appropriate velocity factor for your cable) of feedline, which adds 180 degrees of delay. The result would be a net zero phase shift, so the antennas would still be in phase. Note this isn’t much different from stacking linearly polarized antennas. One way to think of it is that you have a stack of horizontally polarized antennas, and another stack of vertically polarized antennas, and they just happen to be on the same booms and be 90 degrees out of phase. That’s all circular polarization is , and stacking doesn’t fundamentally change the picture.

Tags: antenna (Prev Q) (Next Q)

Q: How to increase antenna aperture? Tags: antenna (Prev Q) (Next Q) I know that in the short wavelength region, where parabolic antennas are used, the aperture can be increased simply by making the dish larger, as is the case with the radio telescopes. But how to do this in the RF? If I make a half wave dipole larger, its resonant frequency decreases. The other way I can imagine is to make an array of antennas working in phase, but in this case it gets more directional with larger number of elements. Is there a way to increase antenna aperture without making it directional? Tags: antenna (Prev Q) (Next Q) User: tr00rle Answer

by phil-frost

Is there a way to increase antenna aperture without making it directional? Not really. You can make the antenna more efficient by reducing losses, but since antennas are usually designed for minimum loss already, there is probably no significant gain to be made in this direction unless you are starting with an electrically small or poorly designed antenna. Radio telescopes do operate “in the RF”, so what applies to them also applies to any other antenna. Increasing the dish size does increase the effective aperture. It also increases directionality. If you didn’t know it already, effective antenna aperture (A eff) and gain (G ) are essentially two ways of specifying the same thing. They are related by the equation: 4πA eff G= λ2 Assuming our antennas are already as efficient as we can make them, then we can’t increase the aperture, or equivalently, gain, without also increasing directionality. Here’s why. Consider you have a 1W transmitter. If you send that power equally in all directions, then you have an isotropic radiator which has by definition a gain of 1. Let’s just say you found a way to increase the gain of this isotropic radiator without also increasing its directionality. That is, it has a gain greater than unity, but still sends energy equally in all directions. Were you to construct such a device, I would surround it with a Dyson sphere , which would capture all of the energy it transmitted. If your device had a gain of 2, then the 1W transmitter would be emitting 2W of power for my Dyson sphere to capture. I could then use the output of that Dyson sphere to power another instance of your device, giving me 4W. I could go on cascading instances of this device and obtain limitless power. It’s a perpetual motion machine, so probably is impossible. By reciprocity , it can be seen that the same thing is true when receiving. I can make an antenna array which has some greater gain in some direction, but it must necessarily have

less gain in some other direction for some given phasing configuration. If you provide a way to vary the phasing of the antenna, such as combining the signals from each element independently and dynamically in software, rather than in hardware, then you can pick the best phasing for a particular signal which might come from any direction. However, this requires that “best” is defined and measured dynamically. Modern radio communication systems do this, for example MIMO in 802.11n . However, it adds complexity to the system, and I guess might be considered as “cheating” as far as your question is concerned. Alternately, you can provide an additional source of energy as an amplifier. This adds gain to all directions, so you could say it increases antenna aperture. Because you must supply the amplifier with additional energy, it is not a perpetual motion machine. While we use amplifiers all the time, we don’t usually consider this as increasing gain or aperture because that way of thinking isn’t very useful. If the antenna directionality is not increased, than the amplifier increases noise as well as signal. That is, the signal to noise ratio remains the same. Tags: antenna (Prev Q) (Next Q)

Q: What sort of radiation efficiency can one expect from a folded dipole? Tags: antenna (Prev Q) (Next Q) It is pretty well established that folded dipoles have much greater acceptable-SWR bandwidth than ordinary dipoles . Radiation efficiency input power.

is simply the quotient of radiated power to the antenna feedpoint

Seeing that folded dipoles are able to achieve the greater bandwidth without introducing a designed-as-lossy element (a technique not unheard of with large-bandwidth antennas), what is the effect on radiation efficiency of using a folded dipole as opposed to a regular dipole? Are there any considerations affecting folded dipoles that would not affect a regular dipole antenna erected in the same physical location which would have a noticable impact on the radiation efficiency? For the purpose of this question, assume otherwise identical conditions; identical height over ground, identical ground, identical possible parasitic elements, identical feedline, etc. Also, note that I am not asking about the radiation pattern of the folded dipole; I am only concerned with the antenna’s radiation efficiency here, unless some other factor has a noticable impact on the radiation efficiency as compared to a regular dipole. A great answer would look at this from both the perspective of a same-wire-length antenna (meaning approximately double the folded dipole’s physical length) as well as a same-physical-space antenna (meaning effectively half the radiator length). Tags: antenna (Prev Q) (Next Q)

User: michael-kjörling Answer

by phil-frost

For all practical purposes, the radiation efficiency of a folded dipole versus an ordinary dipole is the same. Consider, they are essentially the same antenna.

simulate this circuit

– Schematic created using CircuitLab

The only difference is that in the folded dipole, we’ve replaced the feedpoint with a short. Since the Thévenin equivalent resistance of a voltage source is 0Ω, this doesn’t make a lick of difference to the currents in the antenna. The currents are the same, the fields are the same. Everything is the same, except that the voltage source now sees only half the current. So then, what is there that could affect radiation efficiency? There is nothing. There might be some difference in ohmic losses, depending on if you allow the folded dipole to have twice as much copper or not, but this is a very small contributor to loss. More significant for terrestrial antennas is ground losses in the Earth, but having established that the fields around a dipole and a folded dipole are the same, how could the losses be different? They aren’t. The same reasoning applies to any other kind of loss. Tags: antenna (Prev Q) (Next Q)

Q: How does a Dual Band Handheld Antenna work? Tags: antenna (Prev Q) (Next Q) Looking to get a (highly recommended) NAGOYA NA-771 37cm “Dual band (2M/70cm) handheld antenna” for my Baofeng UV-5R. If my math is correct - this is about a half-wavelength antenna for 70cm, but doesn’t seem to correlate to anything for 2m.

What does this mean? Is it really good for 70cm but no so much for 2m, or am I misunderstanding the principals/construction of this antenna. (Also, it’s just a handheld antenna, so it’s not a “dipole” nor does it have an evident “ground” - so I might not just understand what it “is”). Tags: antenna (Prev Q) (Next Q) User: brad Answer

by phil-frost

A half-wave dipole, or a quarter-wave monopole, are resonant on their fundamental frequencies and all odd harmonics thereof. 2m and 70cm have that harmonic relationship, 70cm being approximately the first odd harmonic of 2m: 144MHz ⋅ 3 = 432MHz So, an antenna that looks like a half wavelength on 2m will look like 1.5 wavelengths on 70cm. Although the radiation pattern is different, the antenna impedance is the same, and so will provide a good match to the radio in either case. Keep in mind that handheld antennas are usually monopole antennas, like a vertical. They are approximately equivalent to a dipole of twice the length. There is no obvious ground plane as there is with a vertical because mobile antennas usually sacrifice performance for size. See How do Handheld antennas work without ground? For further reading, I suggest , which expands on some math and shows diagrams of radiation patterns under various conditions. Tags: antenna (Prev Q) (Next Q)

Q: Are antennas circuits? Tags: antenna (Prev Q) (Next Q) For an antenna to work, doesn’t charge have to flow through it? A current must be present. To me it indicates it must be a circuit, but how is a dipole a circuit? If they are not circuits, then how does charge flow in them? Tags: antenna (Prev Q) (Next Q) User: mikew Answer

by phil-frost

What do you mean by “circuit”? Do you mean there’s a loop of conductor from one side of a battery to the other, possibly with some other conducting components along the way? How about this circuit?

simulate this circuit

– Schematic created using CircuitLab

Is there a circuit here? There certainly isn’t any way to follow a line from one side of the battery to the other. Each half connects to opposite plates of the capacitor, and those plates are separated by an insulator. Yet, if you flip that switch repeatedly, the LED will blink. Clearly there’s some current flowing. If we pull the plates of the capacitor apart, it’s still a capacitor. It capacitance will decrease, but it’s still a capacitor. Just a smaller one. If we squish the plates into long, thin tubes or wires, it’s still a capacitor. Capacitance may decrease still more due to the smaller area of the plates, but it’s still a capacitor. The circuit now is looking something like this:

simulate this circuit

What if we now pull the ends of the capacitor apart?

simulate this circuit

Yep, it’s a dipole antenna. Lose the LED and the resistor, and flip the switch a few million times per second, and you have a transmitter. Not illustrated here is also the inductance of the antenna. All circuits have inductance, which you can realize if you follow a similar argument but with an inductor instead of a capacitor, and start straightening the coil into a straight line. The inductance decreases, but it never goes away. Usually we don’t draw the inductance because it’s small enough to be negligible in a simple circuit that blinks an LED. Thus, antennas have capacitance and inductance. They also have resistive losses (unless they are made of superconductors) and radiation resistance . Putting all these together, antennas can be modeled as an RLC circuit . Answer

by kevin-reid-ag6yo

The idea that a closed circuit — a loop — must be present for current to flow is a

simplified description, which is only true for simple DC circuits. It’s a simplification that works because in the DC case, if there is no complete circuit and yet current is flowing, then charge is accumulating somewhere, and the electric field from that excess of charge will oppose the current, increasing to the exact point at which the current stops.† However, in the AC case — and RF is AC, or perhaps “beyond AC” depending on how you classify things — the current is expected to reverse, and therefore those accumulations of charge can go away again, so the system can pass through repeating cycles of charging and discharging. The common circuit component in which this happens is a capacitor. The movement of charge in a dipole antenna is somewhat like that in a capacitor, with “the rest of the universe” substituting for the space between the capacitor plates. Like in a capacitor, no charges actually move from one half of the antenna to the other (except indirectly through the rest of the circuit). Instead, the charges bunch up in the antenna, forming a positive excess on one half and a negative excess on the other. In a receiving antenna, the energy to push the charges together comes from the incoming wave. In a transmitting antenna, it comes from the transmitter. As the wave continues through the rest of its cycle, the antenna discharges and charges in the opposite polarity. Thus, the rest of the circuit connected to a receiving antenna “sees” an oscillating voltage corresponding to the original wave. † Actually, it’ll increase a little bit further and reverse — sloshing back and forth a bit until

it settles down. This is due to inductance. But that doesn’t matter for the rest of this answer. Tags: antenna (Prev Q) (Next Q)

Q: How is RF a radio receives just not a mishmash of eletromagnetic energy? Tags: antenna (Prev Q) (Next Q) So at any given time, electromagnetic waves of many different frequencies are flooding the space around me. I have a little 2 meter radio. Are not all these electromagnetic waves exciting the electrons in the antenna at the same time? Let’s just go out on a limb and say the only RF reaching my radio is 2 meters. Let’s just say frequency 146.120 and 146.805. If the radio is getting hit with both these frequencies at the same time, how is the antenna providing the voltages for just the one frequency that it is tuned to? It doesn’t but then I’m not understanding how an antenna can receive multiple frequencies at the same time. Seems it would be just a jumble. Tags: antenna (Prev Q) (Next Q) User: mikew


by kevin-reid-ag6yo

Filters. A filter is a circuit which is designed to react differently depending on the frequency. Every real (not mathematically ideal) circuit element does this to some degree, but filters are designed to have a very specific frequency response. Here’s a very loose and incomplete high-level schematic of a simple radio receiver:

simulate this circuit

– Schematic created using CircuitLab

As you can see, the filter has four terminals: two for the input from the antenna, and two for the output to the demodulator. (In practice, they might more likely share a single ground bus for both input and output sides, for a total of three terminals.) The effect of the filter is that the part of the signal coming from the antenna which has the desired frequency passes through — as if the wires on the left were connected to the wires on the right — and the rest of it does not — as if the wires on the left were either shorted together or disconnected. Filters can be made out of various components, but most commonly inductors and capacitors. Introductions to electronic circuits often say something like “capacitors pass AC and block DC; inductors block AC and pass DC”. This is true, but simplified; there is not just “AC” but the entire spectrum of possible frequencies, and the higher the frequency the more the capacitor will pass it and the inductor will block it. If you put an inductor and capacitor in parallel or in series, you get a circuit with a resonant frequency — a specific frequency (actually a small range of frequencies) which it will pass (or block) much more than other frequencies. That’s the simplest filter. Additional complexity in filter design gets you “sharper” filters that are better at passing what you want and blocking what you don’t want. In addition, the antenna itself has frequency-varying characteristics and therefore acts as a filter. This is why there are different size antennas for different frequency ranges. The above is a very simple picture. The main thing that I’ve omitted (besides e.g. amplifiers, which every radio but a “crystal radio” has in order to produce an audible output volume) is tuning.

One approach to tuning is to adjust the filter’s resonant frequency (or passband) to the frequency you want to receive. Early receivers (see crystal radio and tuned radio frequency (TRF) receiver) did use this technique. However, it is difficult to make a filter that is both adjustable and sharp enough to be good at receiving one station and not also an adjacent one (it has poor selectivity). Instead, modern radios (starting with the superheterodyne design) internally generate a signal at a particular offset from the desired frequency (the local oscillator (LO)) which is combined with the signal from the antenna (mixed) in such a way as to produce a copy of the radio signal at a fixed frequency (intermediate frequency (IF), equal to the offset between the LO and the input) which is then filtered using a sharp non-adjustable filter before being passed to the demodulator. Originally, the local oscillator was an adjustable filter (usually containing a variable capacitor and a fixed inductor) and amplifier connected in a positive feedback loop — the filter selects the particular frequency and the amplifier keeps the signal oscillating. (Here, the filter doesn’t need to be especially sharp because it’s handling only the fed-back signal — which will quickly settle on only the resonant frequency.) Modern radios instead use digital circuits to generate the local oscillator signal, via digital-to-analog converters (DAC) and phase-lock loops (PLL); this allows very precise tuning under computer control. Tags: antenna (Prev Q) (Next Q)

Q: Why must twin-lead conductor spacing be small to avoid radiation? Tags: antenna (Prev Q) (Next Q), feed-line (Next Q) A transmission line does not radiate when the spacing between the two wires is very small when compared to the wavelength, but the transmission line begins to radiate when the spacing between the lines becomes comparable to the wavelength of the signal. Why is this? Tags: antenna (Prev Q) (Next Q), feed-line (Next Q) User: danny-paul Answer

by phil-frost

Twin-lead transmission lines don’t radiate because the opposite fields from each conductor cancel, but when the spacing is far apart this does not happen. First, let’s consider the magnetic field around an infinite, straight conductor with uniform current throughout. In this image, the conductor is just right of center, and the current is coming straight out of the page.

Now let’s add next to it another conductor, with the current going the other way:

Add these fields together, and you get:

For distances far away relative to the conductor spacing, the fields are equal but opposite, so when added together they cancel. Radiation is, by definition, a field that extends to infinity. If there are no fields far away, then it can’t be radiating. However, we made an assumption of uniform current. When the spacing between the conductors is small, this is a mostly true assumption. Although the current isn’t exactly uniform, we must travel many multiples of the conductor spacing before there’s any appreciable change in phase. However, when the conductor spacing is large, then this is no longer true. Remember, the current is reversing direction periodically, and if we look at the field from just one conductor this means the field is alternating between clockwise and counterclockwise swirl. The changes to this field only propagate at the speed of light, so if we zoom the graph out to be a wavelength wide or more, we’d see those changes propagating away as waves.

In the image above, the wavelength appears to be approximately four units. Now if we add that second conductor, two units away, we get this:

Notice how the fields don’t cancel. They don’t cancel because on the scale of the conductor spacing (which is not small relative to the wavelength) there can be significant changes in phase. Thus, there are regions of constructive interference where the fields don’t cancel. These regions extend out to infinity, and thus, the feedline radiates. Images were generated with a Javascript vector field grapher by Kevin Mehall Tags: antenna (Prev Q) (Next Q), feed-line (Next Q)

Q: What is the effect of using different number of radials with ground plane antenna Tags: antenna (Prev Q) (Next Q)

I’m new to electronics and telecommunication at all, I having trouble with understanding the difference between 2, 3 and 4 radials, as I’ve searched online I’ve learned that I can use only 1 radial(and it makes sense) but when using 2, 3 or 4 its to supply a counterpoise to the ground(balance?). Other source talked about 2 radials: The object of the two radials is to produce a canceling signal in the horizontal plane. They do this by being driven together. However, they must radiate a canceling field. That means they must be matched to radiate. Is the above quote also apply to 4 radials and anyway what is true is it only for balance or canceling maybe I’m confused and its about both, if anyone can help me make sense from all I will be very thankful. Tags: antenna (Prev Q) (Next Q) User: aviel-fedida Answer

by jsh

Elevated radials not equal to ground plane A common misconception is elevated radials (as counterpoise) perform the role of “ground plane” in an antenna system including dominating the far field effects from real ground over which the antenna resides. Radials perform two roles: a conductive path for the inner shield currents and a method to ensure the radiation from this new path is cancelled in the far field. Your research is correctly touching on these realities, but let’s dig further by examining the two roles. A conductive path for inner shield currents Almost everyone knows the RF currents within a coaxial transmission line have two equal and opposite polarity components. The current from the center conductor energizes the monopole… easy enough. The current on the inside of the shield has many more pathways to follow. Notably, the outside of the coax can entice the current to flow depending on what impedance it presents to the antenna feedpoint. If the antenna electrically connects to the mounting structure, it too can entice currents to flow. Enter a single radial… A conductor trimmed to 1/4 wavelength at the operating frequency is a form of impedance transformer. Since the free end of the radial is open, it maintains a high impedance by definition. Following the transformer logic, this high impedance transforms to a low impedance at the other end. If we connect this Low Z point to the shield/mountingstructure at the feedpoint, it will provide a low impedance and tend to draw a large proportion of the inner shield current to itself. This radial, thus energized, radiates. We have solved half the problem with monopoles… namely we have reduced the current flow

on the outer transmission line and mounting structure by monopolizing the current flow into the radial with its manufactured low impedance at said feedpoint. This logic doesn’t necessarily hold true if the outer shield of the feedline or mounting structure also presents a Low Z in parallel with the radials, but let’s assume for the moment the radials win the “current” battle. With current flowing upon it, the single radial is free to radiate its energy exactly like the monopole element. Cancelling far field effects by adding another radial… If we add a second radial opposite the first, the same action occurs with both receiving the lion’s share of current divided equally between them. The symmetric orientation of the two radials is such each both radiate, but because their polarities are opposite each other by way of orientation, the far field summation from both is negligible. It isn’t zero, but is so small to be of no consequence so long as the radials are 1/4 wavelength or less. Two problems solved Thus providing two radials, one opposite the other, solves two problems for us: manhandling the shield inner current and ensuring this current doesn’t affect the far field of the antenna pattern. What tests have to say Simulation and direct measurement both confirm just two radials of 1/4 wavelength or less result in almost zero perturbation of the monopole far field radiation pattern leaving the monopole element alone in determining the radiation circular symmetry. Note the induction fields (stored energy fields) of each radial are not balanced in the nearfield. Thus it is possible to greatly perturb the far-field balance if one radial is too close to some mounting structure or another conductive object. With each radial containing half the shield current energy, they are each more sensitive to nearby conductors. Add more radials Continuing the theme, adding more radials almost completely eliminates any microscopic deviation from a pure circular far-field pattern. Three or four radial monopole antennas are the most popular configuration. One interesting consequence of adding still more symmetrical radials to the base of a monopole antenna is raising the capacitance between the radials and monopole. The net effect of this is each radial can now be a bit shorter in length. See “Hats, Number of Spokes, and Capacitance” and “Two Radials are Enough” in the article about the AHVD antenna for more details… More radials also means if the energy present in one is perturbed by placing a conductor in

its induction fields, the net effect is “out voted” by the numerous non-perturbed radials. The consequence of radials One particularly unwanted byproduct of using radials, and one that caught me by surprise when I finally figured it out, is the raising of the elevation angle. I’ve suggested above that radials contribute little to no effect on the important far-field pattern in azimuth. What about elevation. Measure any classic 1/4 wave ground plane antenna and you will see elevation on the primary lobe. Look at figure 5 in this web page… Note the measurements (not simulations) of two monopoles (one over a metal place, the other with four radials). They both exhibit an upward tilt. If one simulates the radial monopole with a source right on the feedpoint, but without any mast or feedline component, the far field elevation pattern looks like the classic doughnut shape you get from a standalone dipole, less a bit of gain. So why the difference. If you add the feedline outer conductor and/or a mast to the simulation model you wind up tilting the pattern upwards and get agreement with measurements. The problem is the radials induce currents into the mast/feedline, encourage a mast current and thus tilt the elevation pattern. This fascinating effect is often erroneously credited to the radials somehow “reflecting” the signal upwards just like a metal sheet, but is in fact due to induced energy on the mast/feedline beneath the antenna. This is easy to confirm in any antenna simulation tool. Conclusion Two or more radials shorter than a 1/4 wavelength and arranged symmetrically produce little to no effect on the circularity of the monopole azimuth far field pattern. Radials induce energy to the mounting structure and/or feedline generating the typical uptilt in the elevation far field pattern. Tags: antenna (Prev Q) (Next Q)

Q: Minimum thickness of whip antenna Tags: antenna (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q) I’m looking at designing a communication system using very low power transmitter (0.1 W) and operating in the 400 Mhz range. For my uses I think a quarter wave whip antenna would work well, so I’ve calculated the length of the antenna to be 187.5 mm.

So far so good (I hope). Now I’m looking at how light I can make this antenna. My understanding is that an antenna of this sort is essentially just a bit of wire of the appropriate length (187.5 mm), but I can’t figure out if there’s a minimum thickness of the wire. The only limitation I can think of is a thinner wire has higher resistance and hence will heat more quickly (causing more noise). Is this really the limitation? I’ve never seen a very thin whip antenna and I fear there may be a reason behind this. Tags: antenna (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q) User: fraserofsmeg Answer

by phil-frost

At such a low power, durability is probably more of a concern than anything else. A few simplifying assumptions and quick calculations will demonstrate this. The impedance of a quarter-wave whip is highest at the tip and lowest at the base. That is to say, the current is lowest at the tip, and highest at the base. So if we can demonstrate that the wire gauge is sufficient at the base, where current is highest, then it should be sufficient for the rest of the antenna, also. Given your transmit power: P = 0.1 W And the impedance of a quarter-wave vertical at its base: R = 36 Ω And Joule’s first law: P = I 2R We can solve this system of equations for I and figure out what the current at the antenna base must be: 0.1 W = I 2 ⋅ 36 Ω 0.1 W =I2 36 Ω −−−−− 0.1 W √ =I 36 Ω 0.053 A = I So the question is now how small a wire can you use to carry (at maximum) 53 mA. You can look at a wire gauge chart and see the answer is “pretty damn small”, especially considering we calculated the current at the maximum and it is less everywhere else in the wire. There’s another way you might approach the problem: you can calculate (again referencing a wire gauge chart) the resistance of some proposed wire. Then compare that resistance to the 36 Ω radiation resistance of a whip to get an estimation antenna efficiency:

antenna efficiency =

36 Ω

antenna efficiency =

36 Ω 36 Ω + resistance of wire

I say estimation, because to properly apply this formula you must transform all the impedances to the impedance they would have at the feedpoint, but remember since the impedance is at a minimum at the feedpoint, were you to go through the trouble of doing that you would end up with a smaller resistance and a higher efficiency. And so you can look at this and see that even if your wire has a 1 Ω resistance, you still have at least a 97% efficient antenna. And a wire that’s a quarter-wave long at 440 MHz and has a resistance of 1 ohm is a really thin wire. Tags: antenna (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q)

Q: Antenna length in relation to lambda length Tags: antenna (Prev Q), jargon (Next Q) I’m pretty new with antenna stuff. I’m not sure how to understand antenna length in relation to lambda with dipole antennas. If a simple dipole antenna is lambda/4, has it a total length of lambda/2 (every pole lambda/4 long) or a total length of lambda/4? Tags: antenna (Prev Q), jargon (Next Q) User: leathlon Answer

by kevin-reid-ag6yo

Terminology can be ambiguous here; there is no universal standard for how to describe antennas. That said, here are some heuristics: If someone says, e.g., “a 20-meter dipole”, they mean an antenna which is for the 20meter band, i.e. almost 10 meters long from end to end (because a full-size dipole has an electrical length of λ/2). If someone says the length of a dipole antenna is some particular value, then they mean the length from one end to the other — the physical space taken up by the antenna — which will be λ/2. In the US, if they specify a length in feet, then they’re almost certainly referring to the physical length. I don’t know if there are any clues like this in other countries. As far as I know, no one ever uses the λ/4 value in discussing dipole antennas, unless they’re giving instructions for cutting the wires to the proper length. Answer

by cavrecon

Also, don’t get confused if you see actual, physical antenna lengths shorter than theoretical wavelengths/lambdas.

Because the dipole legs are made of real-world components in complex situations, “velocity factor” comes into play which will tweak the numbers slightly. Many guides give you nice numbers to make the math easier, but almost always advise that these are starting lengths, almost always longer than needed, so you will trim the antenna to best resonance. Tags: antenna (Prev Q), jargon (Next Q)

United States Skip to questions, Wiki by user dan-kd2ee This tag should be used for any questions about US-specific regulations, including questions about operating privileges, secondary users, regulatory rules about interference caused by or to amateur operators. It can also be used for questions about clubs or other organizations using ham radio in the USA or for questions about nets that specifically target the USA. This tag should not be used simply because the person asking the question is in the USA, it should only be used if the answers need to be specifically directed towards US rules or practice.

Questions Q: How to operate IEEE 802.11 WiFi AP within the amateur radio service? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) How can I properly use my ham radio license to operate an IEEE 802.11 WiFi access point within the US amateur radio service, rather than the US “part 15” regulations for unlicensed transmissions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: david-anastasio Answer

by michael-kjörling

IANAL, but based on my limited knowledge of US amateur radio regulations: Disable all encryption, as encrypted communications are not allowed within the amateur radio service. Yes, WEP counts as encryption, too. So does HTTPS, SSH or SMTP with STARTTLS. One of the few things you can allow is plain-text HTTP. Set the network SSID to your call sign. This should be enough to identify the transmissions. Force select a channel which is within the boundaries of the amateur radio band. This should put you within the limits of the amateur radio service and allow you to operate the access point under the regulations relevant to amateur radio. Answer

by joseph

All the info you could ever want is being provided on this website.. They are using WRT54G routers for ham band wifi usage. There is a great community for support and lots of documentation..Type “ham mesh net” into your favorite search engine and you will find many answers. Answer

by dcaswell

In 2006 the ARRL dropped its support for changing the rules to allow digital encryption. The rationale for their decision is that it was already legal. Their reasoning comes for the following FCC rule: Part 97 : Sec. 97.105 Control operator duties (a) The control operator must ensure the immediate proper operation of the station, regardless of the type of control. The ARRL interprets this rule to mean that encryption to ensure the integrity and control of one’s operations is legal. This document

explains the entire rationale.

In the United States no Control Operator has ever faced any disciplinary action for

encrypting their WIFI transmissions as long as the encryption mode (but not the key) is public. The article has lots of cautions, for example: Every control operator is still responsible for periodically transmitting their call-sign. It recommends you use your wifi-SSID for that purpose. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Secure communication over Amateur-band HSMM / 802.11 in the United States Tags: united-states (Prev Q) (Next Q) I’m quite interested in 802.11 over amateur radio frequencies; however, all I have done at this point is reading (I don’t have a ham license yet). The conventional wisdom (espoused in this ham.SE answer) is that you cannot encrypt radio communications at all. This limitation seems to fly in the face of normal countermeasures used to secure data transfers through the internet. So encryption is off the table; however, that still leaves issues such as authentication and data integrity. I have read that CRAM-MD5 hashes are sometimes used as part of data services implemented over 802.11 ham radio, because CRAM-MD5 hashes are allowed under the FCC rules. The contents of messages signed with CRAM-MD5 are always visible; yet, the authorship of the message can be verified (because CRAM-MD5 works in the same way that PGP does). As best I can tell, using CRAM-MD5 leaves you vulnerable because: It does not perform mutual authentication (i.e. the client can’t verify the server’s identity) It’s possible to run off-line dictionary attacks against captured hashes (although the underlying HMAC-MD5 hash doesn’t have the same vulnerabilities as MD5 ). The bigger concern to me is a man in the middle attack, since CRAM-MD5 offers no mutual authentication between client and server. This kind of vulnerability is also the kind of dynamic that makes PEAP worse than no 802.11 authentication (since PEAP doesn’t enforce mutual authentication between the wifi client and RADIUS server, like EAP-TLS does). It has been shown that weak PEAP clients freely offer their password hashes to a wifi AP masquerading the same SSID as the real AP. My concern with 802.11 over ham frequencies is determining that I’m giving my password / data to the right endpoint on the other side (and not an attacker). Questions Is there another authentication scheme besides CRAM-MD5 , that is both legal in the US and performs mutual authentication? If I wanted to implement an authenticated HTTP service over ham radio, is there

another authentication scheme that I should consider besides CRAM-MD5


Tags: united-states (Prev Q) (Next Q) User: mike-pennington Answer

by amber

I’d say your best bet is to avoid handing over your hashed password entirely. Instead, use a zero-knowledge authentication scheme; see this security.SE question for more details . Zero Knowledge Authentication will make it so that it doesn’t matter who you “give” your response to - even if a malicious server requests authentication (or intercepts other authentication), it doesn’t actually learn anything about your password. If you incorporate the response to the zero-knowledge auth as part of the public-key signed request, you should be able to formulate a system that both (a) is signed by the client, and (b) does not reveal information to 3rd parties that would allow them to forge future requests, since the zero-knowledge challenge response would form a nonce. As far as verifying the server goes, a public key signature should suffice. (Previous response, before OP clarified…) IANAL, but… There is a difference between encryption and authentication. The former requires no one to be able to tell what data is being passed; the latter requires no one to be able to produce something that is accepted as legitimate without some (non-public) knowledge. For instance, public-key based signatures allow for authentication of a message’s sender without obscuring the contents of the message. As long as you’re okay with the content of your requests being visible but not forgeable, you could probably use such a public key system without running afoul of the FCC regs. If, on the other hand, you don’t want anyone to be able to see what’s in your requests and responses, you’re out of luck. Again, IANAL. Tags: united-states (Prev Q) (Next Q)

Q: What regulatory issues/differences should I be aware of as a US ham vacationing in Europe (Poland)? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) I am a US ham with an Extra Class ticket. If I were to go Poland (or possibly some other part of Europe) on vacation and bring some radios, what legal stuff do I need to know about? I know that my Extra Class license converts into a CEPT license under the reciprocal operating treaty, but what does that mean for me with regard to frequencies,

power levels, and things like that? Do I have to register somehow before operating? The information on the Internet seems a bit sparse. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: krzysz00-kf5soq Answer

by gdc

There are a few important things you will need to remember, which are mainly outlined here and here . I believe you must follow the power limits and band plans as outlined by the Polish government while operating there. Information will be hidden somewhere in here . Good luck with that. I believe your best bet would be to email some people on those pages and hope for the best. You won’t need to register with anyone in Poland when you arrive, but you will need to be carrying the documentation described in the first two links above. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Why is an exemption for music given to NASA broadcasts of manned space flight missions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) FCC 97.113 Prohibited transmissions reads: (e) No station shall retransmit programs or signals emanating from any type of radio station other than an amateur station, except propagation and weather forecast information intended for use by the general public and originated from United States Government stations, and communications, including incidental music, originating on United States Government frequencies between a manned spacecraft and its associated Earth stations. Prior approval for manned spacecraft communications retransmissions must be obtained from the National Aeronautics and Space Administration. Such retransmissions must be for the exclusive use of amateur radio operators. Propagation, weather forecasts, and manned spacecraft communications retransmissions may not be conducted on a regular basis, but only occasionally, as an incident of normal amateur radio communications. It is also a test question on the Technician license, that the only time that music can be transmitted using an amateur radio license is incidental music transmitted as a part of an authorized rebroadcast of a manned spacecraft and an Earth Station on a US Government frequency, when NASA has given permission for such. I have a few questions about this: 1. Why does this exception even exist? 2. Has this been used for significant events, such as the Apollo Moon Landing? Or ever, to anyone’s knowledge?

Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: pearsonartphoto Answer

by adam-davis

Prior to the internet getting a continuous stream of audio from a manned space mission was difficult, even when the mission was overhead, but, of course, due to orbital mechanics it often isn’t overhead. Amateur Radio enthusiasts would request and often gain permission to retransmit audio of space flights, and with some coordination and planning you could listen to space transmissions without having particularly expensive radio equipment - a few users would do the heavy lifting, and broadcast it as it passed overhead for them, and you’d simply tune into their retransmission. However, licensed amateur radio users aren’t permitted to use their station for general broadcasting, and specifically restricted from playing music over the air. These two rules prevented space mission broadcasts (which occasionally did feature music), and so a special rule was provided that, with permission, users could retransmit such transmissions for other enthusiasts. It’s not commonly used now because NASA itself provides continuous broadcast access to most of their missions live via the internet, but in the heyday of the Apollo and similar space race programs Amateur Radio was often the only way to tap into these transmissions which were rarely broadcast via more general methods such as radio and television for exceptional events. In fact, it would be surprising to me if they gave specific permission now unless good reason was provided as to why the internet streams couldn’t be used. Keep in mind that this rule is an exception. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Why do Amateur Radio organizations in the United States oppose the relaxation of encryption prohibitions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) I saw this question stating that it is illegal to encrypt traffic, at least in the US and UK. I also heard that there was recently an attempt to get the FCC to loosen this restriction, but a lot of hams argued against it. Why do Amateur Radio organizations in the United States oppose the relaxation of encryption prohibitions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: dan-kd2ee Answer

by adam-davis

The issue came up recently when one amateur radio user petitioned the FCC to permit

encrypted communications for emergency operations complying with HIPAA health privacy laws.

with the primary goal of

The ARRL urged the denial of this petition , and the FCC subsequently denied the petition . The major points of the ARRL’s arguments were: it is ARRL’s considered view there is no factual or legal basis for the assumption that encryption of transmissions…is necessary in order to continue and enhance the utility of Amateur Radio emergency and disaster relief communications The ARRL also turned away Rolph’s assertion that the current prohibition in §97.113 “has impacted the relationship of Amateur Radio volunteers and served agencies and significantly limited the effectiveness of amateurs in supporting emergency communications.” The League said it’s unaware of any evidence that served agencies have been reluctant to utilize Amateur Radio as part of their emergency or disaster relief communications plans because of the encryption restrictions in Part 97. The League characterized as “erroneous” and “unfounded” Rolph’s assumption that encryption of certain information may be required under the provisions of HIPAA — the Health Insurance Portability and Accountability Act. Radio amateurs, the ARRL countered, are not “covered entities” under HIPAA, which applies only to health care providers, health plans and health care clearinghouses. there is no expectation of privacy in Amateur Radio communications. There is no evidence that emergency communications has been hampered by this issue, nor that care agencies subject to HIPAA have been reluctant or unwilling to utilize Amateur Radio services in emergency communication and disaster planning Adding the duty to encrypt certain transmissions to emergency communications workers would increase their workload. They did suggest that this need not be a permanent ruling, “However, the ARRL said that should it become necessary in the future for radio amateurs to protect the privacy of individuals whose medical data may be transmitted by Amateur Radio during or after an emergency or disaster, “the Commission may be asked to revisit this matter.” Answer

by user303

So as another take on it, you can engage in the thought experiment of “what happens if encryption is legal”. Let’s say you’re a taxi operator and you want to dispatch via radio. Well usually you’d need a commercial license to do this, since amateur radio is strictly non-commercial. But if you can encrypt your traffic, who’s to say it’s commercial or not? You’d save a few bucks in the process, but that’s not the point of the service. The FCC doesn’t have the resources to keep an eye on the amateur service. They rely mostly on self-policing, and it works fine. But that would be impossible if the traffic was encrypted - you wouldn’t be able to tell the taxi service from two buddies talking about the game. Finally, ham radio is “supposed” to be public, experimental, academic, etc. Anybody can homebrew a rig or antenna and send more-or-less any signal they want subject to the rules - but anybody else can hook their rig up to their computer and decode it, or maybe even

send it themselves. Everybody has the chance to learn from everyone else, and encryption would take that away. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: What defines music, per amateur radio regulations? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) Sometimes when I access IRLP nodes, they have a very short melody telling you that you are connected; or when my local repeater’s net begins, it does the famous doorbell 8-note sequence. What is the fine line of prohibited and allowed with respect to music? Is it that overtone usage, like a Sine-wave 6 tone melody, is allowed, but if a piano is used, it would be prohibited? Or is it the length, like a 2-second little access melody, is allowed, but it can’t go on forever? Or is it what we define as common music, like a 3 minute song, would be prohibited, but random sequences of sine waves for a few seconds would be allowed? DTMF in a sense could be avant-garde music from John Cage or Karlheinz Stockhausen, who loved the sounds on his shortwave radio and incorporated all of the unique sounds he heard in his music. So what breaks the barrier for the FCC rules on music or other non-voice audio transmissions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: skyler-440 Answer

by pearsonartphoto

FCC 97.113

states that the following is prohibited:

(4) Music using a phone emission except as specifically provided elsewhere in this section; communications intended to facilitate a criminal act; messages encoded for the purpose of obscuring their meaning, except as otherwise provided herein; obscene or indecent words or language; or false or deceptive messages, signals or identification. Looking around, the best I could find is that this rule is intended to prevent general purpose broadcasting, specifically with the purpose to entertain. From this website, there is an interesting quote on music but it is worth considering:

. I wouldn’t take this as law,

Similarly, the transmission of music is also prohibited (with one exception: music incidental to an authorized retransmission of communications from the Space Shuttle

is permitted). However, there is reportedly a ruling that one ham singing “Happy Birthday” on the air to another ham does not count as the “transmission of music”, presumably because most hams seem to be unable to sing. Again, this is a noncompete regulation; if you want to transmit music the FCC wants you to use the broadcast service or a low power service to accomplish your purpose, not amateur radio. If your interest in radio is to be an on-air DJ, again, amateur radio might not be for you, and you should consider looking elsewhere. Bottom line, if something that is purely incidental to the conversation, or if you are transmitting it digitally, you can actually have a bit of music and not get your hand slapped by the FCC. Thus, the doorbell seems fine, and most likely the types of “Windows Sounds” that sometimes come up, but personally, I wouldn’t risk it. If you are trying to broadcast then you are almost certainly in violation of the law. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Is Morse code allowed on FM Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), cw (Next Q) Let’s say I get my little 2 meter FM handheld out and make a little sine-wave generator with which I pulse a morse code and if I connect it to headphones a speaker, I hear the dits and dahs of a nice sine wave tone. Now let’s say I connect this to the microphone port on my transceiver with the VOX setting turned to detect when I am entering the morse. Is this allowed, or is it illegal because of the wasted bandwidth when I could just use carrier? My country is the USA. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), cw (Next Q) User: skyler-440 Answer

by dan-kd2ee

Completely legal. In fact, it’s common practice to identify repeaters (both in the amateur service and in public safety/commercial) with exactly this method. That said, you likely won’t make many QSOs with it. There aren’t many people who would be prepared to immediately respond if they started hearing FM morse on 146.52 (the typical hailing frequency for simplex operators on the 2m band), compared to people down in the CW section of the band. Answer

by james-nf8i

tl;dr: It’s legal on any VHF or above frequency where phone modes are permitted. It is not allowed on HF or below, nor where phone modes are not allowed. What you have described is called “Modulated Continuous Wave” (MCW), as defined in

the US amateur radio rules under 47 CFR §97.3(c)(4), and would have the emission designator F2A. (The usual CW used on HF has emission designator A1A.) In areas regulated by the FCC, it is not legal on frequencies below 50.1 MHz, between 144.0 and 144.1 MHz, or between 219 and 220 MHz. It is legal on any other amateur frequency. MCW is commonly used for automated identification of FM voice repeaters. It is worth noting that some software capable of transmitting the many HF digital modes via an SSB transceiver can also generate CW in the same fashion. When transmitted this way through an SSB transceiver, it is technically emission designator J2A, which is still within the definition of proper CW. In areas regulated by the FCC, proper CW is legal on any frequency allocated to the amateur service (subject to certain limitations on the 60m band). Sources: 47 CFR §97.3(c)(1), 47 CFR §97.3(c)(4), 47 CFR §97.3(c)(5), and 47 CFR §97.305(c) Wikipedia: Modulated Continuous Wave Wikipedia: Types of Radio Emissions Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), cw (Next Q)

Q: Is Alaska considered to be located north of line A? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) I recentley moved to Fairbanks AK, and was wondering if Alaska constituted being north of line A. Being that geographically, Alaska is north of line A, but in real world applications, Fairbanks is nowhere near Canada. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: david-anastasio Answer

by chris-wiegand-k0den

Reading , I cannot find that any part of Alaska is “north of line A”, but some of it may be “east of line C”. Line A doesn’t start until Aberdeen, Washington, so to be north of that line you would have to be in the northern Continential US or in Canada. Alaska is not geographically north of that line. This is why there’s a Line C - to cover the Canadian/US border shared with Alaska. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Is Morse code a requirement for ham licensing? Tags: united-states (Prev Q) (Next Q), license (Next Q), cw (Prev Q) (Next Q) As I recall, it used to be in the U.S. that the ability to read and send Morse code over CW was a requirement for an amateur license (and was tested, I believe). Is that still true in the U.S.? If not when was it dropped? Around the world, is Morse a requirement for amateur licensing? Tags: united-states (Prev Q) (Next Q), license (Next Q), cw (Prev Q) (Next Q) User: mgkrebbs Answer

by pearsonartphoto

It is not required any more for any US license, as of 2008. It has not been required for the technician license since 1991. It is still required in some areas, and some international amateur radio licenses, in particular the IARP license, which may be used by US amateurs to operate outside of the US in IARP countries. Bottom line is, however, that fewer and fewer countries are requiring it, ever since the 2003 ruling from the ITU that no longer required knowledge of CW for operating on HF. Answer

by vk6db

In Australia, the requirement for Morse was dropped when the new licence structure of three classes (Foundation, Standard and Advanced) was adopted. This happened in October 2005. Since that date there has been no requirement for any Australian amateur to demonstrate proficiency in Morse for any class of licence. Answer

by user669

Apart from Licensing, CW is required for using some specific frequencies. For a U.S. list of such frequencies see this ARRL page: Tags: united-states (Prev Q) (Next Q), license (Next Q), cw (Prev Q) (Next Q)

Q: Using my Baofeng UV-5R to talk to walkie talkies Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), ht (Prev Q) (Next Q) I have a few walkie talkies at home and sometimes I connect my UV-5R to them to talk to them and act as another walkie talkie. At one time, I built a little simplex repeater out of it. Should I not be doing this? I don’t think the other walkie talkie users care about me doing this, just knowing the FCC, they might freak out or something crazy. I used the 462.562 frequency.

Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), ht (Prev Q) (Next Q) User: skyler-440 Answer

by adam-davis

The GMRS and FRS bands are governed by the FCC and have specific requirements not just for use and power output, but for equipment that is allowed. One of the requirements is that radios used for GMRS service be part 95 certified and FCC certified for GMRS use: §95.129 Station equipment. Every station in a GMRS system must use transmitters the FCC has certificated for use in the GMRS. Write to any FCC Field Office to find out if a particular transmitter has been certificated for the GMRS. All station equipment in a GMRS system must comply with the technical rules in part 95. The FRS rules are just as strict: §95.194 (FRS Rule 4) FRS units. (a) You may only use an FCC certified FRS unit. (You can identify an FCC certified FRS unit by the label placed on it by the manufacturer.) (b) You must not make, or have made, any internal modification to an FRS unit. Any internal modification cancels the FCC certification and voids your authority to operate the unit in the FRS. (c) You may not attach any antenna, power amplifier, or other apparatus to an FRS unit that has not been FCC certified as part of that FRS unit. There are no exceptions to this rule and attaching any such apparatus to a FRS unit cancels the FCC certification and voids everyone’s authority to operate the unit in the FRS. (d) FRS units are prohibited from transmitting data in store-and-forward packet operation mode. The FCC does not have a process to self-certify radios, so you can’t declare the radio certified. If you have an Amateur Radio license you’ll find that the FRS and GMRS frequencies aren’t available under that license. So according to FCC rules, your use of the UV-5R is not acceptable on that frequency. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), ht (Prev Q) (Next Q)

Q: How do I renew my FCC amateur license? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) I have a technician class license, and my license expires in March 2014. How do I renew my license?

I received a notification in the mail from W5YI-VEC informing me that I could renew my license through them. They included a form that I can fill out and mail to them, along with a $7.00 fee. Is there a way to renew directly with the FCC? What are the advantages and disadvantages to renewing with a service like W5YI-VEC? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: ben-miller Answer

by rhaig

The ARRL renewals page (

) says:

Amateur applications can be filed manually using paper forms or electronically over the Internet. Amateurs may electronically renew their FCC-issued licenses “on line” via the FCC web using FCC ULS . FCC permits on-line renewals at 90 days or less before a license will expire, and when the license has expired but is still within the two-year grace period for renewal. Licenses that have been expired for more than two years are not eligible for renewal or reinstatement. If you have a Vanity License renewal, remember to have your credit card accessible to pay the FCC Regulatory Fee. Amateurs may also renew their licenses within 90 days before the license expiration date, or within the two-year license grace period after expiration, by using FCC Form 605 by mail to: FCC, 1270 Fairfield Rd, Gettysburg PA 17325-7245. Vanity Renewals will also need to submit FCC Payment Form 159 and the required FCC Regulatory Fee, along with the FCC Form 605. After completing both forms, you can mail your FCC Form 605, FCC Form 159 and your payment to: FCC, Wireless Bureau Applications, PO Box 358130, Pittsburgh, PA 15251-5130. Licenses that have been expired for more than two years are not eligible for renewal or reinstatement. For a complete list of FCC filing instructions and filing fees go to the ARRL page Instructions for License Renewals or Changes. Basically you can either use ULS online at job=home Or download form 605 ( ) and file manually. From what I can tell, the W5YI site just makes it easier to fill out the forms, and they file it for you. I can not determine any specific advantage to using their site. The only disadvantage I can discern is the additional fee for their service. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: What is the body of knowledge the U.S. written exams test?

Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) I’m considering getting a U.S. amateur radio operator license. If you want to study to pass a license test, there are many resources to learn the answers to the entirety of the question pool: online practice exams and study aids, “ham cram” courses, etc. I came across one document (not quickly finding the link again) which basically takes the entire question pool and rephrases each question into a paragraph which briefly describes the broader topic and gives the question and answer as an example of that topic. But I’ve looked through the question pool, and it seems obvious to me that the questions are not comprehensive; just like any test one might find in school, they are intended to sample your grasp of a larger body of knowledge. So, where’s a copy of the syllabus for “U.S. Amateur Radio 101”? What topics should the holder of a Technician, General, or Extra license have knowledge of? What would be the content of the question pool if test-takers had infinite patience, and could be tested on every fact rather than a sampling? Or, addressing my actual plans: what topics should I ensure are contained in my study materials, given that I remember best when I have theory rather than only disconnected facts, and I’ve looked at what the question pool is testing and it seems worthwhile to me to also know the material that obviously could be in the pool, but happens not to be, but I also fully expect to learn just-in-time as I start projects, so material which is neither on the test nor “you need to know not to do this” is a lower priority. If I just wanted to pass the test, then judging by some online practice tests, I could get all the way to Extra on my electrical knowledge, common sense, and a bit of luck, but that’s not what I want to do! (I could ask “What book/resource is appropriate for this learning style?” but that would be shopping . If you have such a suggestion, you could turn that into a description of what it covers and how that is relevant.) Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: kevin-reid-ag6yo Answer

by wprecht–ab3ry

If I just wanted to pass the test, then judging by some online practice tests, I could get all the way to Extra on my electrical knowledge, common sense, and a bit of luck, but that’s not what I want to do! I think that they body of knowledge they are testing may once have been fairly focused, but it has become a bit muddled by attempts to include new technologies without completely losing touch with the roots of the hobby. At least that is my perspective as someone who took the Tech exam, then the General 4 weeks later and the Extra 4 weeks

after that. A simple summary is this: The rules (FCC Part 97) Operating practices, including customs not required by FCC rules Amateur radio “technology”: operating modes, types of antennas, etc. Enough physics to understand propagation and basic electronics Basic electronics sufficient to understand, build and maintain basic radio equipment Safety practices (physical, electical and RF) For someone who’s technically oriented, the new material is really just the first 3 items. Like you I wanted to be sure I understood the material so I could fully participate. As you have already guessed, it’s completely impractical to comprehensively test anyone. Again, as a new ham myself, some glaring omissions in the testing is actual operating practices: how to get onto a repeater and what the protocol is for participating, similar for HF nets, contest rules and practices, what the heck are all these knobs for on this radio? I think in other countries they include a practical portion on the test and these things have to be known in advance. I didn’t have an Elmer (teacher/mentor), I just got the books and did the tests and didn’t get a radio until I was a General, so all this had to be learned on the fly and took a while. If you have access to a live ham, this part will go a lot more smoothly for you. I am still learning what some of these knobs do 6 months later… As @Phil Frost related, it’s pretty easy to just pass the test if that’s your goal. The US tests are 4 distractor multiple choice tests with 74% for mastery. So you need only 28 out of 35 for the Technician and General tests and 37 out of 50 on the Extra class test. The tests are constructed such that each section of the material is represented by at least one question. Answer

by phil-frost

If I just wanted to pass the test, then judging by some online practice tests, I could get all the way to Extra on my electrical knowledge, common sense, and a bit of luck, but that’s not what I want to do! That’s how I did it. Many of the questions are about electrical engineering, having to do with antennas, feedlines, Ohm’s and Joule’s laws, Smith charts, and so on. The higherclass tests have more of this. If you are well-versed in RF engineering, can do basic arithmetic, and read a polar graph, you are set in this department. There are also questions about regulations. If you really want to study the body of knowledge itself and not the question pool, then go read the FCC’s part 97 . But really, most of this falls under common sense (don’t declare an emergency because you can’t find your keys) and the rest is rote memorization (the 20 meter band starts at 14 MHz). Reading the rules directly is dry, painful reading, and it all boils down to “operate within the allocated frequencies, and don’t be a jerk” anyway. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: Is any licensing require to receive in the amateur radio bands? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) I’m considering hosting a foxhunt for a local youth group (scouts, in this case), and one of the questions asked was whether those searching for the hidden transmitter need have a license of any sort. Will they need licenses if they are handling amateur radios, but only intending to receive transmissions? If they don’t need a license, are there precautions or steps I should take to ensure compliance with laws and regulations during the hunt? This will occur in the US, north of Line A, if that affects the answer. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: adam-davis Answer

by wes-hardaker

As discussed, yes it’s perfectly legal to receive anything. It’s the transmitting that is regulated. One easy solution is to not use a transceiver at all. Since the transmitter half of the device is your problem. So take the transmitter out of the transceiver and you end up with just a receiver. So what can you use as a receiver? The simplest thing to use would be a scanner! There are many many hand held scanners that can receive things in the HAM bands and if you used one, then you don’t need to worry about giving it to someone that isn’t allowed to transmit. You could also “build your own” and the good news is that building receivers is a lot less complicated and expensive than building a transmitter, and there are lots of project instructions online or even available for purchase with parts that would let you build your own for fairly cheap. The trick is building one for the transmission mode you want to use during the game. For something like FM, for example, there should be some generally available FM receiver parts or ICs that you could use. Answer

by amber

In general, reception of radio signals does not require a license. (Even if a government wanted to try, it’d be nearly impossible to regulate - after all, there’s inherently no emission from a reception-only station, so there’s no way to tell it’s even happening.) A license is only required for a transmitting operator. The HTs you’re using for the hunt are probably transmission-capable, but if there’s a way to prevent them from easily being keyed on (e.g. if you can preset a frequency, set a reasonable squelch, and then turn on the keypad lock) that would probably help to prevent accidental transmission. If you wanted to be on the safe side, and had the human resources available, you could also have a licensed ham accompanying each group, in which case they could act as the control operator for the radio (and thus satisfy licensing requirements, as long as they’re

also willing to hold responsibility for any transmissions). Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: Moving from Australia to the US, Amateur radio license transfer? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) Moving from Australia to the US, is there a way to transfer my license in any way, or do I need to sit the exams in full? I’m wondering if there is any concept of “credit” towards licensing, so I wouldn’t need to sit all three exams (assuming I was going for Extra). Edit: Moving permanently. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: david-vk2vxk Answer

by k7aay

There is no reciprocity agreement between Australia and the USA, and the US Federal Communications Commission rules for amateur radio licensing and operations also do not provide for any way to get a license except by taking the test(s). Answer

by pearsonartphoto

There isn’t a way of transferring the credit towards a permanent license. Luckily, the US exams consist of a large degree of practical knowledge. Bottom line is, you should be close to getting the same level of license from your knowledge base. I’ve periodically taken the tests, and I score higher ever time than I did when I was studying originally, because I have learned through working with Amateur Radio the knowledge included in the test. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: How do I notify and publish information on experimental modes? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), modes (Prev Q) (Next Q) I’m considering tinkering with a new mode. Of course I’ll stick to experimental channels and low power for now, but as people notice my transmissions they won’t immediately understand what is being transmitted. How do I disseminate information that shows others how to receive and read my transmissions so as to avoid the appearance of encrypted or secret transmissions? Do I have to disseminate that information before I start my testing, or can I do the testing, finalize the design, then publish? What I’m worried about here is that as the mode evolves and changes, keeping already published information up to date is time consuming, and I’d rather publish a little overview, do the work until it’s complete, then publish the final

details. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), modes (Prev Q) (Next Q) User: adam-davis Answer

by oh7lzb

Back, before the Internet, the documents were published in magazines, conference papers and such – well after the protocols were designed and initial tests were done. In some cases CWID (transmitting callsign using CW every now and then) has been used to make sure the transmissions are well identified even if the actual data is a bit hard to decode. Nowadays, I think, people usually just experiment quite freely and publish when they have something ready. If you’re really worried, you can always do testing transmissions with a dummy load, keeping the radiated power so low that it cannot be considered a licensed transmission at all. After all, you can generally transmit on any frequency, any power, as long as you don’t radiate that energy. If you’re tinkering with a new mode, it might actually be easiest to do it using a simulated predictably noisy multipath software environment without initially involving real radios at all! Publication method ideas: Set up a blog or wiki site, let people know roughly which frequencies you’re using, your callsign, and some general information about the mode. Open Source is the hip thing to do nowadays. Consider pushing your development code on Github or some other similar code repository - that’s what I do myself. Your current code serves as pretty definite documentation as it is. As an added bonus you get an off-site backup of your code, and it might even attract other developers to help out. Answer

by james-taylor

I’ve been doing some experimentation as well and met the same issue. The way I’ve been dealing with it is to use a CW tag before and after the mode (as well as sometimes alongside my data mode). In it I put my callsign, and a tiny url (as its morse) e.g. if my experiment data was at, i nip to tinyurl and get a tinyurl:, so I would transmit: [CALLSIGN] EXPERIMENT SEE - HTTP TINYURL COM 2TX [CALLSIGN]

and hopefully people understand that without the punctiaton. The page itself is generally a blog page containing information on what I’m doing - not necessarily anywhere you can download a file to decode or instructions, but importantly I put a contact form or a way of getting in touch if I’m causing interference. I currently pre-code the audio files that I transmit, and can overlay that morse alongside the data blob so it goes out like a margin notes.

The rules (in the UK) say you can’t transmit secret codes, and the essence of my work not being public isn’t that I’m being secret, just that I’m not ready to publish the source (thats arguably an interpretation). In practice it wouldn’t take long for someone to analyse and decode the message as mine are all PSK based of underlying data. Software testing with generated noise etc is good, but doesn’t always let you test reality. I probably do 99% of my tests with just audio connections between overplayed with static etc, which lets me tinker without having to make real radio connections between people. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), modes (Prev Q) (Next Q)

Q: What are the (US) rules about unlicensed low-power transmissions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), power (Prev Q) (Next Q) It is common wisdom that transmissions of any sort (perhaps unidentified, encrypted, in the FM broadcast band, etc.) are permitted if they are sufficiently low power. Where are the FCC regulations which permit this, or where can I find a wellaccepted interpretation of said rules? People say they are in Part 15, but I read (well, skimmed) Part 15 and found mainly rules about offering equipment for commercial sale. I am specifically interested in permission for DIY or experimental transmitters and transmissions. I am also interested in how these rules compare to those applying to devices transmitting in the “ISM” bands; is the latter equal or lesser in restriction? (I am aware that while this question may be amateur radio, it is not about the Amateur Radio Service; I am asking it here in the hopes that it is a topic of sufficient interest to the community and that the relevant expertise is present.) Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), power (Prev Q) (Next Q) User: kevin-reid-ag6yo Answer

by adam-davis

Overview Title 47 Part 15 defines regulations which cover any device that 1. Radiates RF, whether intentionally, unintentionally, or incidentally 2. Doesn’t require an individual license for operation While a device might not require an individual license to be operated, it may still require FCC testing. This applies most strongly to devices made to be sold to others, which is why you see a lot of commercial references. Just because you are not commercializing your device, though, doesn’t make you immune to the regulations affecting commercial devices. In fact the only difference between home built devices and commercial devices in

this section is that home built devices are not subject to testing, verification, and declaration of conformity. They are otherwise subject to all the same rules. Regulation summary for home built, non-commercial, intentionally radiating devices Here is a list of some (out of many) of the regulations you will have to follow whether your device is commercial or not. Your device must: 1. not cause harmful interference, and must accept any interference caused by other devices that follow the regulations they are subject to. (15.5.b) 2. be disabled upon notice from the FCC that the device is causing harmful interference. (15.5.c) 3. be designed and constructed in accordance with good engineering design and manufacturing practice. (15.15.a) 4. be designed so that any user-operable controls do not allow the device to operate outside the limits of these regulations (15.15.b) 5. be labeled correctly (15.19) 6. be built for personal use, not marketed, not constructed from a kit, and built in quantities of five or less (15.23.a, 15.201b) 7. not transmit more than spurious RF inside restricted bands detailed in 15.205. 8. not conduct emissions onto the AC line, if connected to the AC line, greater than the limits specified in 15.207. General RF field limits For intentional radiators devices must not emit a field strength stronger than specified for the frequency ranges measured at the distance specified: MHz Field Strength (microvolts per meter) Measurement distance(meters) 0.009 - 0.490 2400/F(kHz) 300 0.490 - 1.705 24,000/F(kHz) 30 1.705 - 30 30 30 30 - 88 100 3 88 - 216 150 3 216 - 960 200 3 960 - ∞ 500 3

Unless otherwise specified under Additional Provisions and elsewhere(15.211-15.2xx) any intentional radiator following all other regulations is not restricted to any specific mode, modulation, or transmission scheme. (15.215.a) Note that most of these bands have additional provisions Answer

by k7aay

Page 15 of the FCC’s OET63 specifies maximum emission of 100 µV/m measured three meters away, for consistent transmission in the US FM broadcast band, and 250 µV/m if you can keep the bandwidth down to 200KHz or less. That would permit Codec2 , FreeDV , Olivia , PSK63 , Pactor-I , RTTY , Q15X25 and many other digital modes.

Now, when you’re talking about ISM, there are multiple bands available in the US and that link shows the frequencies and permitted bandwidth, which you can match up with the FCC table in the first line about for power limits. If, forex, you’re talking about the 902-928 MHz band, you have 26 MHz to play with and up to 1W output power for spread-spectrum use, so the answer is a qualified YES, depending on which ISM band band you want to use. Also, the Hobby Broadcaster website

may be a useful resource for you as well.

Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), power (Prev Q) (Next Q)

Q: What is the best practice when tuning an antenna on air? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), procedure (Next Q) I have a magnetic loop antenna that takes a long time to tune and of course, while tuning it, I need to be transmitting. What is the best procedure for tuning on air? I understand I need to check the frequency and identify myself before transmitting, but what if I’m nowhere near resonant when I do this? I’ll just be getting louder and louder as I reach resonance, and probably no one heard me calling that I was performing a test initially. So I guess my first question is, what’s the procedure from start to finish for tuning on the air? Keeping in mind, I can’t quickly tune with my radio; due to the magloop, tuning is very specific and the SWR is too far out for my radio to automatically fix this. It’s a very long process to tune it properly. Also, is it acceptable to simply put out a carrier signal while tuning? This is definitely more accurate and quick than tuning against a phone transmission, but is it allowed? I’m located in California in the United States in case this is a locale specific answer. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), procedure (Next Q) User: david-vk2vxk Answer

by wprecht–ab3ry

I am pretty sure this isn’t covered explicitly in Part 97 and probably falls under the “don’t cause intentional interference” clause. The practice I was taught is this: 1. Tune off the pileup you found several KHz to a ‘clear’ spot 2. reduce power to the either the lowest the rig will go or the least that will facilitate the tuning process 3. Switch to CW mode 4. key the transmitter (hold down the PTT) and tune away When you are done:

1. Unkey the transmitter 2. Go back to SSB mode 3. Go back to full power (I forget to do this more often than I would like to admit) 4. Tune back to where you were Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), procedure (Next Q)

Q: Aside from repeaters, what station types allow automated transmissions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) I know repeaters don’t have to have a control operator at the radio in order to transmit given certain conditions are met. Are there any restrictions to setting up automated stations which transmit upon receiving specific transmissions from their operators or other operators, but do not act as repeaters? I know beacons are a special case in that they transmit on a schedule. What restrictions apply to unattended, automated stations? The specific problem I’m trying to solve involves automating a connection between two distant radios. The originating radio needs to make several transmissions in sequence due to a user instructing it to, without giving it specific frequencies, sequences, and data to transmit (ie, the radio decides what to transmit). The receiving radio, however, may not have a control operator nearby. It still has to listen, and if it gets a “call” from the originating radio it needs to respond, even if there’s no control operator nearby. Under what rules would this type of automation be acceptable? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: adam-davis Answer

by pearsonartphoto

Digital signals are allowed, so long as they follow this FCC regulation


§97.221 Automatically controlled digital station. (a) This rule section does not apply to an auxiliary station, a beacon station, a repeater station, an earth station, a space station, or a space telecommand station. (b) A station may be automatically controlled while transmitting a RTTY or data emission on the 6 m or shorter wavelength bands, and on the 28.120-28.189 MHz, 24.925-24.930 MHz, 21.090-21.100 MHz, 18.105-18.110 MHz, 14.0950-14.0995 MHz, 14.1005-14.112 MHz, 10.140-10.150 MHz, 7.100-7.105 MHz, or 3.585-3.600 MHz segments. (c) Except for channels specified in §97.303(h), a station may be automatically controlled while transmitting a RTTY or data emission on any other frequency

authorized for such emission types provided that: (1) The station is responding to interrogation by a station under local or remote control; and (2) No transmission from the automatically controlled station occupies a bandwidth of more than 500 Hz. [60 FR 26001, May 16, 1995, as amended at 72 FR 3082, Jan. 24, 2007; 77 FR 5412, Feb. 3, 2012] In any case, if there’s a human on one end, I would think it would be considered remote control, and thus eligible for those rules. But just in case, I would stick to these regulations. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Can I transmit anything inside a faraday cage? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), license (Prev Q) (Next Q) Can I perform any transmission regardless of my license as long as I’m inside an RF sealed enclosure, such that no RF will be detectable from my transmissions off my property? I imagine the answer is yes, but I’d like to be sure I understand. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), license (Prev Q) (Next Q) User: adam-davis Answer

by kevin-reid-ag6yo

I don’t have an answer actually clearly applicable to this situation, but a couple of related scenarios come to mind: Every shielded digital electronic device is radiating “inside a RF sealed enclosure”. Your scenario is different in that it’s not a discrete device with built-in shielding. Part 15 §15.211 permits tunnel radio systems to “operate on any frequency” provided that the emissions meet usual limits as measured at the tunnel mouth. However, this specifically applies to “a tunnel, mine or other structure that provides attenuation to the radiated signal due to the presence of naturally surrounding earth and/or water”, and not artificial shielding. These are two cases where analogous things are occurring; neither one applies specifically here but they’re both precedents which match the common sense “if no one else can receive it, it’s OK”. This does not mean that it’s actually legal. Answer

by wprecht–ab3ry

This is pretty much the same as transmitting into a dummy load (or using the stock rubber duck antennas :) ). I don’t think a canonical answer is possible; Part 97 is silent on the issue. But, if no one can hear you, you can’t be interfering with anyone or “using” the spectrum, so I would say sure. Depending on what you are planning on doing (and on which bands), you might want to make some RF checks at the edge of your property to be sure you aren’t leaking RF. Answer

by pearsonartphoto

I’m trying to find a better source, but according to this letter from Boeing petitioning the FCC in 2011, an experimental license is technically required to operate even within a Faraday cage, although they have an unofficial policy of permitting such actions. Finally, the Commission should codify its policy of permitting entities to conduct experiments within RF enclosures, such as anechoic chambers or Faraday cages, without an experimental license. This makes sense as someone would have to complain before the FCC was involved. And such a chamber should be able to reduce the RF power going out to almost nothing, making the odds that someone complains very miniscule. Still, it could happen. If you use low power in such a device, you probably will be fine. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: Relicensing after a decade, can I reacquire my old call sign? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) The background, I got a US Tech+ license back in the 1990’s when I was in middle school. At the time I did it for the novelty of getting licensed in something and not a bit to imitate my brother. Since I wasn’t using the license at the time I let it lapse in the 2000’s. Now I am thinking of relicensing to either Tech or General. The question though is could I petition the FCC to let me have my old call sign or would I have to just get a new one? I checked out the FCC website and couldn’t find any relevant information in the publications or FAQs. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: bsteinhurst Answer

by adam-davis

Once you are re-licensed and obtain a new automatically generated call sign, you may request your old call sign as a “vanity call sign”. If it isn’t presently assigned to anyone else, you’ll be given it. You’ll have to pay the fees for the vanity call sign, though, there’s no other way for you to re-license under the old call sign after the two year waiting period. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: “Coaxial capacitors in line” in E4E04? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q), rfi (Prev Q) (Next Q) I’ve been studying the U.S. license examination question pools. For the most part, it is reasonably obvious what the questions and answers mean even when I am not yet able to come up with the answers on my own. However, the correct answer to this question in the Extra class pool is confusing me: E4E04 (D) How can conducted and radiated noise caused by an automobile alternator be suppressed? A. By installing filter capacitors in series with the DC power lead and by installing a blocking capacitor in the field lead B. By installing a noise suppression resistor and a blocking capacitor in both leads C. By installing a high-pass filter in series with the radio’s power lead and a low-pass filter in parallel with the field lead D. By connecting the radio’s power leads directly to the battery and by installing coaxial capacitors in line with the alternator leads What is the purpose of specifying “coaxial” capacitors? Why does it say “in line”, which in the absence of further information I would interpret as “in series”? I would think that

low-pass rather than high-pass filtering would be desirable. Is this just a sloppily phrased answer, or is there something subtle here? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q), rfi (Prev Q) (Next Q) User: kevin-reid-ag6yo Answer

by wprecht–ab3ry

Coaxial (also known as cylindrical) capacitors are usually electrolytic type capacitors and are sometimes know as feed-through capacitors when used in automotive applications like is illustrated in the exam question. Feed-through capacitors are designed to withstand very high currents as you’d see across an alternator. The third lead is also to ground reducing the effective series inductance to nearly zero. As to the structure of the component, I imagine placing the leads on opposite sides of the capacitor simplifies construction and reduces the chance of the leads arcing over considering even a modest alternator these days produces 90+ amps. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q), rfi (Prev Q) (Next Q)

Q: Are there any good, consistently receivable signals in the US for HF receiver testing? Tags: united-states (Prev Q) (Next Q), receiver (Prev Q) (Next Q) Having built my first HF receiver, I’d like to know if I’ll need to search around for transmissions that happen to be occurring, or if there are reasonably strong signals I can count on being present regardless of the time or day? I just want a simple test that will tell me it’s working or not without having to set up a sked with someone else, or having a transmitter handy. My receiver is capable of receiving from 1.8MHz to 30MHz. Hopefully there are several signals of interest in this range that are common in the US. Tags: united-states (Prev Q) (Next Q), receiver (Prev Q) (Next Q) User: adam-davis Answer

by kevin-reid-ag6yo

WWV and WWVH broadcast time and frequency reference information continuously, using AM on 2.5, 5, 10, 15 and 20 MHz, so you should be able to pick up all of them using your receiver, given an adequate antenna. At my location (San Francisco Bay Area) with lousy equipment, these signals are only slightly stronger than shortwave broadcast stations, but more reliably present. Answer

by cj5

Another great way to listen for signals, especially stronger ones, other than WWV and WWVH, is to find some active AM broadcast stations within the 1.8 to 30MHz range. Head over to this site , and use the top most form, selecting any station, and preferred language, make sure NOW is checked, and hit GO! YOu can pretty much tune around to the listed frequencies, primarily those listed in red. Canada has a time signal station as well that is fairly strong (as I can pick it up from California) , and pretty much is Canada’s version of WWV and WWVH. It’s frequencies are 3.330 MHz, 7.850 MHz, and 14.670 MHz If you’re outside of North America check this page out for other time stations around the world . It would also be cool to check these frequencies out too, just for fun, to see if you can hear around the world. Tags: united-states (Prev Q) (Next Q), receiver (Prev Q) (Next Q)

Q: What is the permissible frequency error for US amateur radio transmissions? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), license (Prev Q) (Next Q), frequency (Next Q) What are my requirements as a licensed Amateur Radio operator in the US to keep to a single frequency? How much drift can I have during transmission and still be within my license? Does it depend on the mode or band? Note that I’m not asking about the band plan, simply the FCC rules. I’m asking in relation to making transmitters. I’m sure a crystal (20ppm) is more than sufficient, but should I decide to make a simpler oscillator, how much error is permissable? If you want to add how much error is preferable for a given activity (DX, contests, rag chewing, etc) then that’s fine, but please note that I’m primarily interested in what my license permits, rather than what other operators might prefer (at this time, anyway). Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), license (Prev Q) (Next Q), frequency (Next Q) User: adam-davis Answer

by phil-frost

Your frequency error is the difference between where your transmitter indicates you are transmitting, and where you actually are transmitting. The FCC does not regulate where you think you are transmitting. They only regulate where you are actually transmitting. Consequently, your frequency error can be whatever you want, as long as you keep it in the bands permitted by your license. If you are concerned about drift during a transmission, I wouldn’t. Anything you build

today is almost certainly more stable than tube equipment that was built decades ago. Your problem with drift will be that the other station can’t follow you before it is violation of any regulation. Answer

by kevin-reid-ag6yo

Part 97 doesn’t have anything to say about frequency error or drift in particular. The question pool, however, does: T1B09 (D) [97.101(a), 97.301(a-e)] Why should you not set your transmit frequency to be exactly at the edge of an amateur band or sub-band? A. To allow for calibration error in the transmitter frequency display B. So that modulation sidebands do not extend beyond the band edge C. To allow for transmitter frequency drift D. All of these choices are correct Of the sections of Part 97 cited, §97.301(a-e) §97.101(a) is:

merely defines the permitted bands, but

In all respects not specifically covered by FCC Rules each amateur station must be operated in accordance with good engineering and good amateur practice. Thus it would seem that in the opinion of the authors of the question pool, “good amateur practice” includes taking precautions to avoid inadvertently transmitting out of band. Having a well-calibrated and low-drift transmitter would merely be another such precaution. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), license (Prev Q) (Next Q), frequency (Next Q)

Q: What should I do if my call is being used by someone else? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), callsign (Next Q) I’ve been contacted by others who want to verify a DX with me, but I was not operating at that time! It appears that someone made several contacts using my callsign for a short window of time one day. I’ve been keeping my ears open, but haven’t seen it myself, and the only information those who contacted me have are the dates, times, and frequencies of the contacts. What should I do once I find my call being used by someone else? Is there any reporting I should perform to the FCC? Is there anything else I can do besides listening to catch them? If I do hear them, is there a method I can use to at least narrow down their location? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), callsign (Next Q)

User: adam-davis Answer

by kd5qln

If it continues to happen I would report it to the FCC via the FCC’s website here. Answer

by ben-coleman

Were the contacts on the day of a major contest? Chances are that some other station with a callsign close to yours was operating and several operators misread his call as yours. I, too, get the occasional QSL card or eQSL for a time when I wasn’t operating (and they are usually during a major contest). Unless you have definitive proof that someone else was operating with your call sign, at most you might want to return a NIL (Not In Log) response to the operators requesting the confirmation. Answer

by martin-buehring

One time is an error, multiple times seems on purpose. Report it to the FCC in case they violate any laws or frequency uses. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), callsign (Next Q)

Q: CW on phone band Tags: united-states (Prev Q) (Next Q), procedure (Prev Q) (Next Q), cw (Prev Q) (Next Q), phone (Next Q) In the U.S., regulations permit CW operations throughout the amateur bands. That makes the phone section of a band look tempting when the CW/digital part of the band is busy with a contest. I wonder if my friends and I can reasonably have our scheduled QSO in the phone part of the band when the CW/digital part is busy. Is it acceptable to conduct a CW QSO in the phone part of a band? If so, what are good operating practices to avoid interfering with SSB operators? Tags: united-states (Prev Q) (Next Q), procedure (Prev Q) (Next Q), cw (Prev Q) (Next Q), phone (Next Q) User: wayne-conrad-kf7qga Answer

by wprecht–ab3ry

Since we are talking about the United States, the “phone” portions of each band are actually described as phone, CW & image. So it’s not only legal, but it’s perfectly acceptable to operate CW in that portion of the band. Contest rules generally confine contesters to the CW-only portion of the band making the rest of the band a viable option during CW or Digital only contests.

As for good operating practices, they are the same as always: find a clear spot, listen, ask if the frequency is in use, listen, commence operation. Some bands, notably 40m and 80m have some long standing scheduled nets, you’ll want to avoid those, otherwise you should be OK. CW takes so little bandwidth, it’s pretty easy to slide past a CW QSO if you are looking for room to operate SSB. Probably you will want to avoid contest style operation though to avoid causing any misunderstandings. A normal rag-chew style QSO will likely not bother anyone. Tags: united-states (Prev Q) (Next Q), procedure (Prev Q) (Next Q), cw (Prev Q) (Next Q), phone (Next Q)

Q: What’s the difference between national calling frequency and national simplex calling frequency in the 2m and 70cm band plans published by ARRL? Tags: united-states (Prev Q) (Next Q), arrl (Next Q) On the 2 meter and 70 centimeter band plans published by the ARRL, what is the difference in intended use between the calling frequencies (144.200, 432.10 MHz) and the simplex calling frequencies (146.52, 446.00 MHz)? Tags: united-states (Prev Q) (Next Q), arrl (Next Q) User: andrew-spiehler-kg5abv Answer

by andrew-spiehler-kg5abv

The simplex calling frequencies (146.520/446.000 Mhz) are intended for FM simplex communication, while the other pair (144.200/432.100) are for SSB. In general use, the term “simplex” implies FM modulation since FM is commonly used in both simplex and duplex operation. SSB, CW, and other modes are generally used for longer distance, simplex-only communication. This answer is based on the discussion Amateur Radio G+ community . Answer

I generated from posting this question on the

by buzzsawddog

144.200/432.100 are intended for SSB Modulation. 146.520/446.000 are intended for FM Modulation. Tags: united-states (Prev Q) (Next Q), arrl (Next Q)

Q: What is the most common amateur identification practice for mobile US amateurs operating in Canada?

Tags: united-states (Prev Q) (Next Q), mobile (Prev Q) (Next Q) When a US Amateur operates in Canada, IT and Canadian regs permit some lattitude on their identification. I have read that some will prefix a “VE3” plus their own home callsign (Ontario, meaning I am in Ontario right now, but my real callsign is the following US one) on their callsign, some will simply indicate that that they are mobile in some way, and some may continue to use their regular callsign without indicating that they are mobile? What is actually most commonly done, and what expectations (if any) does the amateur radio community usually expect from mobile operators operating mobile in a friendly foreign nation, particularly Americans operating in Canada? Tags: united-states (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: warren—ve3wpx Answer

by pearsonartphoto

According to ARRL


Identification for US amateurs is the US call separated by a stroke and the appropriate Canadian prefix identifier (e.g. N1KB/VE3) In every case I can think of, one is required to identify the location from which they are transmitting, if it is not in their call sign, or at least a different country. And usually they want more than just the country, they also want to know the location of the country (VE3 in this case). So any amateur should be following this practice, period. Tags: united-states (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: What Part 97 rule allows unattended, automated transmissions, such as APRS weather stations and beacons? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) What rule allows Amateur Operators to establish and operate remote, automated stations like APRS weather stations or beacons? Are there different rules specifically for beacons, or do they all fall under the same rules? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: adam-davis Answer

by pearsonartphoto

There’s a few parts: §97.109 Station control. (d) When a station is being automatically controlled, the control operator need not be at the control point. Only stations specifically designated elsewhere in this part may be automatically controlled. Automatic control must cease upon notification by a District Director that the station is transmitting improperly or

causing harmful interference to other stations. Automatic control must not be resumed without prior approval of the District Director. §97.113 Prohibited transmissions. (d) No amateur station, except an auxiliary, repeater, or space station, may automatically retransmit the radio signals of other amateur station. §97.213 Telecommand of an amateur station. An amateur station on or within 50 km of the Earth’s surface may be under telecommand where: (a) There is a radio or wireline control link between the control point and the station sufficient for the control operator to perform his/her duties. If radio, the control link must use an auxiliary station. A control link using a fiber optic cable or another telecommunication service is considered wireline. (b) Provisions are incorporated to limit transmission by the station to a period of no more than 3 minutes in the event of malfunction in the control link. (c) The station is protected against making, willfully or negligently, unauthorized transmissions. (d) A photocopy of the station license and a label with the name, address, and telephone number of the station licensee and at least one designated control operator is posted in a conspicuous place at the station location. Beacons have their own rules, which are too numerous to just copy/paste. The section is entitled §97.203 Beacon station., and can be found at ARRL . Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Do I need to actually lock up my station? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) Per §97.103 , one is responsible for the proper operation of one’s station, which of course includes that no unlicensed person uses it to transmit. I have heard suggestions (no link handy, sorry) of taking actual physical security measures such as keeping HTs and critical components with oneself or in locked boxes, or inserting key-switches in the power connections to transmitters. While effective and not infeasible, this seems like overkill to me outside of the presence of children or other unreasonable people. Is there “good amateur practice” about a sufficient standard of prevention? Is it sufficient for me to rely on my judgement that the people I live with wouldn’t do such a thing, nor permit guests to? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: kevin-reid-ag6yo


by adam-davis

That depends largely on your environment. If you have a separate room, and guests, children, and others are unlikely to enter, and more unlikely to touch anything if they do enter, then it’s probably fine to simply leave your radio on and tuned into your preferred frequency 24/7 with the key or mic on the desk. If you need to leave it in the living area with a multitude of children and guests around who have little social conditioning that tells them not to touch things that aren’t theirs, you’ll probably want to switch your output to the dummy load, turn the transmitter to receive only, turn it off, and put away or otherwise hide the key, microphone and other controls as you are able, and turn off the power strip. It would take some knowledge to set up the station so it would transmit, and at that point you might as well have that person tested and then you won’t have to worry. Of course you could lock it up behind a door if you had significant concerns about this, but I haven’t yet run across anyone that felt this level of security was necessary for the purposes of preventing unlicensed transmissions. Usually the lock and key people would put their equipment under was primarily due to concerns of theft for thousands of dollars of radio equipment. If you do have any specific concerns, describe your environment more specifically in terms of location, traffic, people who might have access to it. You’ll probably receive may ideas on how to secure your station while still keeping it easy for you to use. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: How do I change my registered address with the FCC? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) I just moved, and I want to change my registered address with my call-sign. Is there a form or something somewhere that I can fill out? Do I have to mail it, or can I turn it in to the FCC or something electronically? Does it cost anything? What will happen if I fail to get my address updated for a while? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: skyler-440 Answer

by koerner

Here is the link that describes how to update your FCC information. id=amateur&job=cft&page=cft_change_address

I do mine on the website and I have not been charged for it. Within a few weeks a new copy of your license with the new address will arrive in the mail. As for not updating in a timely manner, if you do something that requires the FCC to contact you and they are unable to is when it’s time to worry. I believe fines start around $2700 for that but I may be wrong. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: Does a FCC amateur license cost money? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) If I wanted a FCC Amateur license, is this going to cost me anything? That includes tests, application fees, filing fees, and anything else but hardware. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: awesomeuser Answer

by phil-frost

Fees to obtain a license are set by and payable to the volunteer examiner coordinator . They are typically small to free, and limited by §97.527 to reimbursement “for out-ofpocket expenses incurred in preparing, processing, administering, or coordinating an examination for an amateur operator license.” Some VECs and their fees: ARRL: $15 W5YI: $14 GLAARG: $5 There are many other VECs (14 in total, at time of writing), each with their own fee. Some of the smaller VECs are branches of local Ham clubs and don’t charge any fee at all. Most filings you’d have to do over the life of the license (for example, address changes, renewals) are free to file with the FCC. Most can be done online through the FCC’s Universal Licensing System , so you don’t even need to pay for a stamp. One possible exception: vanity call signs currently cost $16.10 per 10 year license period, payable to the FCC as a regulatory fee. Vanity calls are optional, and systematically assigned calls are still free. Answer

by adam-davis

Typically yes. The only fees paid are given to the test administrator. Sometimes you’ll find administrators that will volunteer to perform testing without fees, making the whole process free. There is no licensing fee, application fee, or regulatory fee. The only fee you might have to pay is a nominal testing fee. Answer

by paul

In 2014 it costs $15 (sometimes less) for taking a license test with your ARRL VEC (Volunteer Examiner Committee). See A license is good for 10 years and renewal directly through the FCC is costless.

Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: Must all three VEs hold the required licence class to “prepare” an examination, or just one? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) 47 CFR § 97.507 states that: (a) Each telegraphy message and each written question set administered to an examinee must be prepared by a VE holding an Amateur Extra Class operator license. A telegraphy message or written question set may also be prepared for the following elements by a VE holding an operator license of the class indicated: (1) Element 3: Advanced Class operator. (2) Elements 1 and 2: Advanced or General Class operators. If a VE team has (hypothetically) one Extra class VE and two Generals, cat the team administer all the elements or just the Technician test? Does the answer change if the Extra does all the work of generating the exams? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: krzysz00-kf5soq Answer

by kc8smi

This answer is for valid for the US only: 47 CFR § 97.507 addresses the preparation of the telegraphy message or the question set. It does not directly address the testing session itself. 47 CFR § 97.509 addresses the testing session. Paragraph (b) states: (b) Each administering VE must: (1) Be accredited by the coordinating VEC; (2) Be at least 18 years of age; (3) Be a person who holds an amateur operator license of the class specified below: (i) Amateur Extra, Advanced or General Class in order to administer a Technician Class operator license examination; (ii) Amateur Extra or Advanced Class in order to administer a General Class operator license examination; (iii) Amateur Extra Class in order to administer an Amateur Extra Class operator license examination.

(4) Not be a person whose grant of an amateur station license or amateur operator license has ever been revoked or suspended. Since all three VEs will need to sign section 2 of form NCVEC 605 then it would make sense that all 3 VEs would hold an operator license of the class indicated it 47 CFR § 97.509. I also found this in the [Volunteer Examiner Manual][1] published by the ARRL: The three or more VEs required to oversee the separate examination area must each hold the appropriate class of FCC license as well as ARRL VE accreditation. So again, it seems that if you want to administer a test, you would need 3 VEs that hold an operator license of the class indicated it 47 CFR § 97.509. [1]: page 46.


Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Identifying regulations for interfering stations Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), rfi (Prev Q) (Next Q), repeater (Next Q) I’m working on tracking down some 2m repeater interference, and I have identified that the offending signal is a spur transmission on a commercial pager service (that lands right on our repeater input frequency). How would I identify regulations that the commercial transmitter should be observing, to verify that their equipment is operating properly, or what are the regulations for a commercial transmitter? (For the purposes of this question, I’m located in the USA) To measure the spur signal, I plan on using a spectrum analyzer to measure the relative magnitude from the fundamental frequency to the spur. I will use an antenna to observe the signal from off-site. Are there potential issues with this method? I’m interested in this approach out of curiosity on whether this is a viable option, not because it is currently necessary. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), rfi (Prev Q) (Next Q), repeater (Next Q) User: w5vo Answer

by w2pks

Your method of measuring the spur signal is perfectly acceptable, and perhaps the best method for this scenario.

Search the FCC database for the transmitter owner that you suspect is on the frequency that’s causing the problem. Contact them given the information within the database. In my experience, groups are responsive to requests to clear up any superfluous signals. If they respond malignantly to your request, it’s time to contact the FCC. Keep in mind that the spur could be a mixing problem with more than one signal involved. For example, 152 MHz and 159 MHz could result in a 145 MHz spurious signal. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), rfi (Prev Q) (Next Q), repeater (Next Q)

Q: Fastest Speed allowed for CW FM repeater ID in USA Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), cw (Prev Q) (Next Q), repeater (Prev Q) (Next Q) What is the fastest legal WPM I can use for my repeater’s Morse code identification? I am in the USA. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), cw (Prev Q) (Next Q), repeater (Prev Q) (Next Q) User: skyler-440 Answer

by pearsonartphoto

20 wpm. §97-119: (b) The call sign must be transmitted with an emission authorized for the transmitting channel in one of the following ways: (1) By a CW emission. When keyed by an automatic device used only for identification, the speed must not exceed 20 words per minute; Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), cw (Prev Q) (Next Q), repeater (Prev Q) (Next Q)

Q: Using ham radio bands for telemetry Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), hf (Prev Q) (Next Q) If I built a machine that went far away, say a buoy, would I be allowed to use ham radio frequencies to transmit telemetry data back to its base station, if I used my call sign? This is for personal research, not commercial applications. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), hf (Prev Q) (Next Q)

User: horse-hair Answer

by n0bml

I don’t see why not as long as you followed the regulations for ID and transmission mode. There are beacons, satellites, balloons and more transmitting telemetry. Beyond the laws I would recommend following the band plans for where to transmit and pay attention to where the signals from your buoy would reach. For example, the lower end of the 70cm band isn’t part of the allowed spectrum in Canada so when I go much farther North I have to pay attention and not transmit on some frequencies I can use in the US. Answer

by scott-earle

Make sure you follow the regulations on ‘unattended operation’. And if you are going to be floating a buoy into the sea, be aware that you may end up transmitting from the territory of another country, at which point your transmission could well be very illegal. If you ended up floating a ‘message in a bottle’ beacon that made its way to North Korean waters, for example, you could create an international incident! Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: Am I studying obsolete information? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) I am using the ARRL General Class License Manual 7th Ed. which was published April 25, 2011. However, I know that the National Conference of Volunteer Examiner Coordinators (NCVEC) recently released the 2015 General Class question pool . Does this mean that the ARRL manual is obsolete and I will have to get a new edition? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: kd8nxh Answer

by phil-frost

The question pools are available online from NCVEC: 2011 pool 2015 pool I downloaded these and ran them through diff

. These are the big changes I noticed:

Section G3E, which is about digital operating procedure, is significantly changed. There isn’t anything especially new technology-wise there, but the question pool is quite different. Additionally, there are new questions related to digital modes peppered throughout other sections. Subelements G4 and G5 have many new or rewritten electrical engineering questions. These questions are largely about electrical engineering. The fundamentals of electricity

haven’t changed, but the question pool has. As long as you are studying the underlying knowledge, and not trying to memorize the answers, you should be fine here. Beyond that, there’s a lot of rewording and clarification and other insignificant stuff. There are some new questions here and there, but not a lot, and they all cover the same body of knowledge covered by other questions. As always, about 70% of them can be answered with common sense. G2B02 (B) What is the first thing you should do if you are communicating with another amateur station and hear a station in distress break in? A. Continue your communication because you were on the frequency first B. Acknowledge the station in distress and determine what assistance may be needed C. Change to a different frequency D. Immediately cease all transmissions For the most part, I’d think the old study guide should be fine. The new pool does not go into effect until July 1, 2015. I couldn’t find any online practice tests (ARRL,, QRZ, and dozens of others offer them for free) using the new 2015 pool, but I bet by July they will be updated. I’d suggest running through that several times before you take the real test, and if you run into any problems with the new questions, remember that you can always get the current question pool online. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: Is it possible to transfer an area-specific call sign from a deceased relative? Tags: united-states (Prev Q) (Next Q), callsign (Prev Q) (Next Q) I passed my Technician exam today and my grandma, who’s been a ham for decades, suggested that I could try to get my grandpa’s call sign. He passed away several years ago, but his FCC registration is still marked active, expiring later this year. From what I’ve read, this would probably be surmountable by making the right kind of notification to FCC and then making a vanity request for it. But here’s the rub: it’s a KH6???, which I’ve read are reserved for pacific island addresses. That makes sense since he probably lived in Hawaii when he got it (and I grew up there), though he kept it for decades after moving to Oregon. Is there any sort of familial transfer process that could get that call assigned to me in California? Tags: united-states (Prev Q) (Next Q), callsign (Prev Q) (Next Q) User: eric-angell Answer


Is there any sort of familial transfer process that could get that call assigned to me in California? There are 3 types of vanity call sign requests: Primary station preference list Close relative of former holder Former primary station holder For your case you can apply for “Close relative of former holder”. Generally, vanity calls can not be assigned outside specific call areas but there seems to be an exception when the request type is “By Close Relative of Former Holder Now Deceased “. Request Types: By Close Relative of Former Holder Now Deceased For your primary station, you may request a call sign that was previously assigned to the primary, secondary, repeater, auxiliary link, control or space station of your nowdeceased spouse, child, grandchild, stepchild, parent, grandparent, stepparent, brother, sister, stepbrother, stepsister, aunt, uncle, niece, nephew, or in-law. An “inlaw” is limited to a parent, stepparent, sibling, or step-sibling of a licensee’s spouse; the spouse of a licensee’s sibling, step-sibling, child, or stepchild; or the spouse of a licensee’s spouse’s sibling or step-sibling. When so requesting for your primary station: - You may request the former call sign of a close relative now deceased even though it has been unassigned for less than two years. Upon the death of the holder, a call sign is assignable immediately to an otherwise eligible primary station of a close relative once it has been cancelled from the database. - You must be an Amateur Extra Class operator to request a Group A call sign. - You must be an Amateur Extra or Advanced Class operator to request a Group B call sign. - You must be an Amateur Extra, Advanced, General, Technician Plus, or Technician Class operator to request a Group C call sign. - You must be an Amateur Extra, Advanced, General, Technician Plus, Technician or Novice class operator to request a Group D call sign. - Your mailing address does not have to be in a Region designated in the sequential system for the call sign requested. A call sign requested by a close relative of former holder now deceased may be in any Region. - You must show your relationship to the deceased person exactly as listed in the

instruction, i.e., “child”, “niece” or “in-law”. More answers to Frequently Asked Questions here


On a separate note, normally vanity calls can not be assigned outside call areas. Normal, in which you were neither a relative of the deceased previous owner of the call nor actual previous owner of the call, applications fall under the “Primary station preference list ” category. Q: My mailing address is in (one of the 48 contiguous states). May I request a Group A call sign designated in Amateur Station Call Sign Systems for Navassa Island? A. No. You do not have an address on Navassa Island where you can receive mail delivery by the United States Postal Service (“USPS”). As a operating aid for ?the amateur service community, certain places such as Navassa Island are designated small blocks of unique call signs. In the Memorandum Opinion and Order, 10 FCC Rcd 11135 (1995), the FCC decided to limit the assignability of call signs designated for these places to preclude the possibility of the call signs becoming quickly depleted. Therefore, Amateur Station Call Sign Systems provides that for Alaska, Hawaii, and the Caribbean and Pacific Insular Areas, only licensees having a mailing addresses where mail delivery by the USPS can be received in the specific state, commonwealth or island can request a call sign designated for that specific state, commonwealth or island.

72 es GL in the application! Tags: united-states (Prev Q) (Next Q), callsign (Prev Q) (Next Q)

Q: Straight to General license, skipping Technician? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) I would like to get involved in ham radio and I’m inclined to study for and take the General exam right away, rather than going for Technician and then upgrading. Are there good reasons not to do this? If this course of action is allowed and not ill advised, then does The ARRL General Class License Manual assume a base of knowledge covered in the Technician Class manual, or can the General Class manual stand on its own for someone starting from no ham knowledge? Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q) User: gregory Answer

by kevin-reid-ag6yo

You can’t take the General exam only, if that’s what you’re asking. What you can do is take the Technician and General (and Extra, should you so choose) exams in one sitting. If you’re going to take an exam at all, there is no reason not to continue to the highest level of examination you expect to be able to pass, unless you want to deliberately limit yourself until you have gained experience. (I haven’t heard of anyone actually doing that.) Additionally, if you initially obtain an Extra class license (I did this), you may be assigned a shorter call sign than you would otherwise — though you can apply for a change, or a specific vanity call sign, later. Shorter call signs are an advantage if you care about how long it takes to speak or send your call sign, such as in a contest. (Technician and General licenses have the same pool of allowed call signs.) As to your second question, if I recall correctly, the ARRL license books are incremental just like the exams — you would need all of the books up to the level you’re studying for. There are other study materials besides the ARRL’s, including free ones on the Web — if you think you might be interested in higher levels I encourage you to just try a free practice test (one such site I used ) and decide whether you’d like to learn the material and how. Tags: united-states (Prev Q) (Next Q), license (Prev Q) (Next Q)

Q: What are the relative bandwidths of the amateur bands? Tags: united-states (Prev Q) (Next Q), hf (Prev Q) (Next Q) While I was operating on 40 m for Field Day, I noticed a higher SWR than when I first set my antenna tuner for the band. This happened, of course, because I was in a different part of the band, but I hadn’t done enough HF operation to expect the result automatically. 80 m is famously so wide that the phone segment of it gets called “75 meters” because the difference matters for antenna design. I’ve heard that what matters for antenna and electronic design is the relative bandwidth — the ratio of the low and the high ends. I’d like to see what this ratio is for all of the amateur bands, and just how much of an outlier 80 m is or isn’t. Tags: united-states (Prev Q) (Next Q), hf (Prev Q) (Next Q) User: kevin-reid-ag6yo Answer

by kevin-reid-ag6yo

The usual figure used in this context is, apparently, fractional bandwidth, defined as the bandwidth divided by the center frequency, and therefore having a range of 0 to 2. f max − f min f max − f min fractional bandwidth = = 2 f center f max + f min Given that definition, and using the United States band edges, here are the fractional (and

absolute) bandwidths of all amateur bands:

This chart was generated using a gnuplot program which can be found in the source of this answer. Answer

by keith-martineau

Here is a chart I made. Hope you find it useful. The numbers are approximate and it depends on your exact method of calculation. I use percentages because that information is easier to find or calculate. This chart is the average percentage using the center frequency (I also have numbers related to each band edge). A lot of people quote a “good” or “well designed” or “average” antenna as having about 10% bandwidth, but it varies a LOT with the exact antenna type in use. The “notoriously wide” bands are 160M, 80M, 10M (despite the smaller numbers), and I would add 6M and 70Cm. Skip code block 160M 10.55% 80M 13.39% 60M 1.36% 40M 4.2% 30M .49% 20M 2.47% 17M .55% 15M 2.12% 12M .4% 10M 5.9% 6M 7.7% 2M 2.74% 1.75M 2.7% 70Cm 6.9% 33Cm 2.84% 23Cm 4.73%

Tags: united-states (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: Is a modded Yaesu FT-270r acceptable to use on MURS frequencies? Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) I am a bit new to the radio scene, so excuse me for any ignorance that may follow. I saw on a website that you could mod the Yaesu FT-270r so that you can increase its transmission range outside of 144 MHz. I have no plans on transmitting outside of FCC designated MURS frequencies. (I am not a licensed ham operator.) Would it be legal and/or OK to transmit on MURS with this mod on this radio? I’d rather find out know then start transmitting on MURS and get in trouble with the FCC for doing so if it is illegal. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q) User: railfancj Answer

by kevin-reid-ag6yo

I am not a lawyer, and this is not legal advice. I’m also not particularly familiar with MURS, and generalizing from other information. According to Wikipedia , MURS (as many other US unlicensed radio services do) requires the use of type accepted equipment. (Terminology note: radio services are CB, FRS, GMRS, MURS, amateur, commercial,

etc.) This means that the only radios you can use on MURS are those which the FCC approves for use on MURS. So, no, your modded radio cannot legally be used. (Modified equipment is only useful on the amateur bands or otherwise on frequencies which you have been granted a specific a license to use.) And in these services which require type-accepted equipment, FCC generally only approves equipment which cannot be used for licensed services — the widely understood rationale being that they don’t want to trust the users of the type-accepted equipment not to use the other functions. Thus, there is no radio which you can legally use in the US which allows transmitting on both amateur frequencies and unlicensed service frequencies. Tags: united-states (Prev Q) (Next Q), legal (Prev Q) (Next Q)

Q: Are hashes (such as md5) legal in the US Tags: united-states (Prev Q), digital (Next Q) If I were to implement a remote computer control system using amateur radio, would using hashes (such as md5, sha-*, etc…) for authentication be permissible under the United States rules? Tags: united-states (Prev Q), digital (Next Q) User: kd8nxh Answer

by pearsonartphoto

Yes, they are. Generally speaking, authentication is legal, obfuscating is not legal. So you could do a cryptographically signed hash that would be legal in the United States to transmit over Amateur Radio. It’s worth mentioning that there is some debate as to how legal a cryptographically signed hash would be. I believe it would be legal, so long as it was a signature, intended to ensure that the message came from a particular person. MD5 type hashes are definitely legal, they merely provide a signature of data already sent, and are used to ensure the data that was sent is correct. Tags: united-states (Prev Q), digital (Next Q)

Legal Skip to questions, Wiki by user community Amateur radio is a highly legislated hobby, and not all of those regulations are always crystal-clear. This tag should be used for questions that are related to the legalities of amateur radio, whether for your home country, other countries or internationally. Make sure to indicate within the question (in the question body and/or using an appropriate location tag) the location to which you want any answers to apply. Questions about legal matters that do not specify a relevant locale are likely to be closed as not answerable without that information. Amateur Radio Stack Exchange is not a forum for legal counsel. If in doubt, always seek professional legal advice.

Questions Q: Encrypted traffic and amateur radio Tags: legal (Prev Q) (Next Q) Am I allowed to send encrypted traffic via any medium or any frequency, or is this completely barred (and thus everything has to be open with no exceptions?) Tags: legal (Prev Q) (Next Q) User: berry120 Answer

by amber

11(2) The Licensee shall only address Messages to other Amateurs or to the stations of those Amateurs and shall not encrypt these Messages for the purpose of rendering the Message unintelligible to other radio spectrum users. From the terms and conditions spelt out by OFCOM (pdf) regulator. Alternately, in the license guidelines

, the UK communications


1(4) The Licensee shall address Messages only to other licensed amateurs or the stations of licensed amateurs and shall send only: (a) Messages relating to technical investigations or remarks of a personal character; or (b) Signals (not enciphered) which form part of, or relate to, the transmission of Messages. Answer

by evan-fosmark

If you are in the USA, check § 97.113 Prohibited transmissions of the FCC rules. Specifically, (4) Music using a phone emission except as specifically provided elsewhere in this section; communications intended to facilitate a criminal act; messages encoded for the purpose of obscuring their meaning, except as otherwise provided herein; obscene or indecent words or language; or false or deceptive messages, signals or identification. As it stands now, encryption is prohibited regardless of your frequency. Answer

by pearsonartphoto

It is prohibited in the US, with one exception. One is allowed to encrypt commands to an amateur satellite (Send from the ground to the satellite). Aside from that, encryption is

prohibited. Tags: legal (Prev Q) (Next Q)

Q: Does mixed-mode operation qualify as a QSO? Tags: legal (Prev Q) (Next Q), modes (Prev Q) (Next Q), procedure (Prev Q) (Next Q), logging (Next Q) Working the bands it’s quite possible to work in mixed-mode, albeit I doubt whether it is ever done. Call this a thought experiment: Station A operates CW

, Station B operates SSB


I find myself wondering What is the legal status of such a QSO? How would it be entered in the log? Is this situation covered by a regulation? Tags: legal (Prev Q) (Next Q), modes (Prev Q) (Next Q), procedure (Prev Q) (Next Q), logging (Next Q) User: vu2nhw Answer

by michael-kjörling

Does mixed-mode operation qualify as a QSO? I’d say absolutely, yes. You’re making contact with another amateur radio station on a frequency allocated to amateur radio; in my book, that qualifies as an amateur radio contact or QSO. What is the legal status of such a cross-mode QSO? Assuming that your license allows you to transmit on the frequency and mode that you are transmitting on, I see no reason why there would be any legal problems with such a QSO. The law can only apply to what you transmit, not to what you receive. It might be possible that in some jurisdictions there are restrictions imposed on what kind of receivers individuals may possess, but even so, I think we have to assume that your possession of the receiver is legal; if it is not, then that’s a completely separate problem. How would it be entered in the log? I would enter the details of my transmission, with a suitable comment in the comments field for the received signal. For example, station A would write mode CW, comment “received SSB” or something like that; station B would write mode SSB, comment “received CW”. One large part of the rationale for this is that if anyone ever complains about your station operating (for example, due to interference), what will matter is your transmissions, not what you received.

Again, certain jurisdictions may have specific requirements. If that is the case in your situation, you should refer to your local regulations for guidance on what exactly to write into the station log. That said, I would expect any such regulations to be centered around the own station’s activities. Is this situation covered by a regulation? I doubt it is, although you’d have to consult your locale-specific regulations to be certain. It may complicate things slightly if you want to use that contact to apply for a modespecific award, but that’s about the only complication I can think of. If you want to claim such a QSO for credit toward a mode-specific award, you’d have to contact the issuer of that award and ask how exactly they will count it. And of course, the QSL card cannot say for example mode 2xCW or mode two-way CW because that would be inaccurate. For a cross-mode contact, I’d probably make it explicit which mode was used by which station, for example by writing mode CW(CL1SGN), SSB(CL2SGN). Tags: legal (Prev Q) (Next Q), modes (Prev Q) (Next Q), procedure (Prev Q) (Next Q), logging (Next Q)

Q: What radio regulations apply in International waters? Tags: legal (Prev Q) (Next Q) What regulations apply to radio operations in International waters? How far offshore does one need to be? Does the answer change between registered commercial vessels and home-made rafts or canoes? Tags: legal (Prev Q) (Next Q) User: hotpaw2 Answer

by andrew-rohne

For registered commercial vessels, you have to have permission from the country of the ship’s registry AND permission from the operator of the ship AND permission from the captain. Source . For being in your own home-made craft, I imagine you just need your license. Note that everything changes when you’re in territorial waters, and I’m not sure how you know (I’d guess maritime charts would indicate where they are). Tags: legal (Prev Q) (Next Q)

Q: Can unlicensed users operate at a Canadian club station? Tags: legal (Prev Q) (Next Q) I am a radio amateur licenced in Canada and a member of a local club station. At a recent meeting, someone asked me whether they could operate at the station if they did not have a radio licence. I am aware that, in general, an unlicenced individual can operate an amateur station with the supervision and presence of a licenced operator, but I am not sure how this rule specifically applies to club stations. 1. Is an unlicenced individual permitted to operate radio equipment at a club station if supervised by a licenced club member? 2. Assuming that an unlicenced individual can use a club station under supervision, which callsign do they use to identify on the air - that of the club station, or that of the licenced supervisor? Tags: legal (Prev Q) (Next Q) User: mtrberzi Answer

by mtrberzi

I forwarded this question to the Radio Amateurs of Canada Regulatory Advisor and received an interpretation. To summarize as direct responses to my original questions: 1. Yes, an unlicenced individual can use equipment at a club station if supervised by a qualified operator. 2. A non-qualified operator should use the call sign an authorized operator would use when operating the station. For a club station, this would generally be the club station call sign. Excerpts from the interpretation (paraphrased): Regarding the first question, about whether an unlicenced individual can operate under supervision. The Industry Canada regulatory document RIC-3 contains the following comment: 1.5 Non-Qualified Persons Non-qualified persons may use an amateur radio station provided a qualified operator is in attendance to perform the control functions. [T]here is no distinction as to the type of station, so this applies to clubs as well as personal stations.

Regarding the second question, about identification. …I didn’t find any Industry Canada guidelines. Certainly the non-qualified operator should use the call sign an authorized operator would use when operating the station. This is usually the club station call sign when operating the club station. That is what I have seen done on field days at “Get-On-The-Air” stations, at stations in museums and science centres, as well as stations operating with a club or RAC call sign for contests. The call sign was not changed when different radio amateurs took turns supervising. [T]he move away from licensing…to certifying radio amateurs left the status of station call signs a little more murky. I am not aware of any firm rules on this so you can use common sense. If your practice is for the ham operating the club station to sometimes use their own call this could be an option when a ham is supervising nonqualified operators. However, the club call sign is always correct. (thanks to Glenn MacDonnell VE3XRA for providing this interpretation) Tags: legal (Prev Q) (Next Q)

Q: Weather Imaging with NOAA satellites - legal? Tags: legal (Prev Q), satellites (Prev Q) (Next Q) I would like to build an antenna for receiving NOAA weather satellites. They’re receivable at around 137.5 Mhz. I’m a total new to amateur radio stuff. I know that it’s not legal to communicate as private person on several frequency areas- so I would like to know if it’s legal to “listen-only” to those satellites on this frequency. I’m here because I haven’t found any sources proofing that it’s legal or not. If it matters, I live in Germany. Tags: legal (Prev Q), satellites (Prev Q) (Next Q) User: leathlon Answer

by yuiu

Here in EU it’s perfectly legal to receive transmission on any frequency. Additional restrictions may apply if the transmission is not mean to be public, for example encrypted Wi-Fi networks or government agencies radios. (source: Telekommunikationsgesetz (TKG) § 89). Answer

by kd5col

Here in the US, it is perfectly legal for you to listen and “download” the satellite data. Since the data is created by a public agency, it is considered to be in the public domain and not subject to copyright. On this website at , you can

find the following: “The information on National Weather Service (NWS) Web pages are in the public domain, unless specifically noted otherwise, and may be used without charge for any lawful purpose so long as you do not: 1) claim it is your own (e.g., by claiming copyright for NWS information — see below), 2) use it in a manner that implies an endorsement or affiliation with NOAA/NWS, or 3) modify its content and then present it as official government material. You also cannot present information of your own in a way that makes it appear to be official government information.” There’s a lot more information there that you should read. I am not a lawyer, but I would assume that with the information being in the public domain and with Germany being a Berne Convention signatory, you should be just fine. You might want to contact your country’s copyright office and make sure, but I use the weather fax as transmitted on HF all the time here. 73, Sean KD5COL Tags: legal (Prev Q), satellites (Prev Q) (Next Q)

Propagation Skip to questions, Wiki by user wprecht–ab3ry RF propagation is the behavior of radio waves when they are transmitted. As a form of electromagnetic radiation radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization and scattering. RF propagation is affected by the daily changes of water vapor in the troposphere, ionization in the upper atmosphere due to the Sun, the frequency of the emission, the path over ground of the transmission. If the path is over-the-horizon path aided by refraction in the ionosphere, it will be influenced by factors that include sporadic-E, spread-F, solar flares, geomagnetic storms, ionospheric layer tilts, and solar proton events. Propagation Modes Surface modes (groundwave) — LF (between 30 and 3,000 kHz) have the property of following the curvature of the earth via groundwave propagation. In this mode the radio wave propagates by interacting with the semi-conductive surface of the earth. The wave “clings” to the surface and thus follows the curvature of the earth. Vertical polarization is used to alleviate short circuiting the electric field through the conductivity of the ground. Since the ground is not a perfect electrical conductor, ground waves are attenuated rapidly as they follow the earth’s surface. Attenuation is proportional to the frequency making this mode mainly useful for LF and VLF frequencies. Direct modes (line-of-sight) — Line-of-sight is the direct propagation of radio waves between antennas that are visible to each other. This is probably the most common of the radio propagation modes at VHF and higher frequencies. Ionospheric modes (skywave) — Skywave propagation, also referred to as skip, is any of the modes that rely on refraction of radio waves in the ionosphere, which is made up of ionized layers in the upper atmosphere. F2-layer is the most important ionospheric layer for long-distance, multiple-hop HF propagation, though F1, E, and D-layers can also play significant roles. The D-layer, when present during sunlight periods, causes significant amount of signal loss, as does the E-layer whose maximum usable frequency can rise to 4 MHz and above and thus block higher frequency signals from reaching the F2-layer. The layers, or more appropriately “regions”, are directly affected by the sun on a daily cycle, a seasonal cycle and the 11-year sunspot cycle and determine the utility of these modes. Meteor scattering Auroral backscatter Sporadic-E propagation Tropospheric modes

Tropospheric scattering Tropospheric ducting Tropospheric delay Rain scattering Lightning scattering Other effects Diffraction Absorption

Questions Q: What is the best time of day/Band to make a contact with Hawaii from the East Coast? Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q) I need to get Hawaii for Worked All States, and live on the East Coast (Virginia). Furthermore, I have a poor antenna, and thus only the prime times of the day seem to really be opened for me. What time of day/band is the best to make the QSO? Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q) User: pearsonartphoto Answer

by quentin-smith

In general, my experience is that band conditions are best for long-distance communication at sunrise and sunset. You generally want the sunset to be somewhere in between you and the person you are talking to, so probably something like 9 PM EST. Beyond that, things like solar weather can make a big difference. I tend to use VOAProp for predicting when and on what band I can best make a contact. The ARRL also publishes propagation charts that show the best time of day. Their November 2013 chart shows that the best time is between 1600 and 0000 UTC, which is noon to 8 PM. Finally, has an interactive web tool that can give you propagation predictions. Finally, remember that power and spectral power density make a big difference as well. 1500W on CW will propagate much farther than 10W on SSB. During good propagation conditions, however, 10W may be all that you need. Answer

by andrew-beals

By my read of it seems as if 10m could be open right now from Virginia. (Virginia, which is a big state, as compared to Rhode Island or Washington DC (not technically a state, but a tiny pin-point on the map)) Your great circle distance from Washington National Airport to Honolulu International Airport is almost 7800km. (calculated here: ) As the Space Weather page explains, the MUF prediction is for a 3000km path (multiply MUF by 1.1 for a 4000km path), which means you’ll have to look for the midway points and hope that your signal bounces an extra time. Looking at the two midway points, I see that the MUF is just about 33MHz. More information here, too:

Also, here:

For a quick peek at what may very well be possible, you could look at the propagation predictor on the home page of

Do remember that this is all “prediction” - this is an experimental service so you must experiment! In ham radio, there are no substitutes for listening or transmitting (on an open frequency!). Often, you may find that you think a given band is dead, but once you call CQ a few times, someone else you haven’t heard yet will pop on and tell you that he’s in the middle of a conversation with someone else you can’t hear. If you’re lucky, the station within earshot will have a conversation or at least a contact with you once he’s done with the other fellow. Many other factors affect your ability to make that contact: Are your antennas radiating in the correct direction? Is anyone listening? Are you scanning the bands to see which stations you can hear and where they’re from? Are you calling CQ? If no-one is listening, you won’t make a contact. If your antennas aren’t right, you won’t make a contact. If the conditions aren’t right, you won’t make a contact. If you don’t call any stations, you won’t make a contact. Answer

by walter-underwood-k6wru

Start with the ARRL propagation forecasts. These are updated every month and there is a specific forecast for the path from the East coast to Hawaii. For a customized prediction, use the online VOACAP propagation predictor here: Finally, you may want to check in with the 3905 Century Club nets. Those are on several bands at several times per day, and are dedicated to WAS and similar awards. Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: Why do concurrent FM signals not mix together? Tags: propagation (Prev Q) (Next Q), physics (Prev Q) (Next Q) Generally when I hear two conflicting signals they do not mix together, but rather one dominates then the other. This phenomenon can be observed on FM broadcast station when driving out of range from one station into the range of another. During the ‘in between phase’ they generally do not mix but rather one dominates and they flip flop being the dominant signal. Why is this? Tags: propagation (Prev Q) (Next Q), physics (Prev Q) (Next Q) User: dan Answer

by dan-kd2ee

I understand why you think it should mix - that’s what happens with SSB, for example. The difference with FM is that in FM, at any instant, each station’s signal is only at one

frequency. If you slowed the signals down and watched through a spectrum analyzer, you could watch the two signals, and you’d see two peaks at constant amplitude, moving independently. The frequency (of the carrier) is modulated based on the audio signal amplitude, so that peak will move within the channel, but it’s always one peak. Your receiver latches on to the stronger peak, and that’s what it decodes. On the other hand, in single sideband, you wouldn’t ever see a single peak no matter how much you slowed the signal down. In single sideband, the amplitude of the carrier is being modulated - it isn’t that the peak is moving, the peak is actually being mixed with (multiplied by) the audio amplitude, so all the peaks from the audio signal would appear on your spectrum analyzer. In this case, there’s no distinction between audio components coming from one source vs another - you could separate the signals if you wanted to using directional antennas, but with a single receiver all you’re going to see is the two signals superimposed. Answer

by walter-underwood-k6wru

This is called the “FM capture effect” and is mostly a characteristic of the demodulator design. Demodulators with a strong capture effect detect the zero crossings of the signal. The zero crossings are only slightly affected by mixing two signals until they are nearly equal amplitude. The steepness of the waveform at zero crossing means that the stronger signal dominates. It takes a larger interfering signal to change the slope enough that the zero crossing moves. FM demodulators usually include an amplitude limiter to increase this effect. Unless the noise happens near the zero crossing in the signal, it is ignored. Effectively, the limiter increases the steepness of the zero crossing. When two FM signals of a similar strength mix, we get the distinctive “doubling” sound heard on repeaters. This distorted signal is caused by the non-linear mixing from the limiter. In an AM envelope detector, the detector is very sensitive to the mixed signals. Also, the signals are linearly combined, so our ears can often distinguish the two signals. Answer

by aa6yq

That’s a property of FM demodulation known as the Capture Effect: when multiple signals are present, only the strongest is demodulated. This does not occur with AM or SSB demodulation, where multiple signals can be simultaneously demodulated. Tags: propagation (Prev Q) (Next Q), physics (Prev Q) (Next Q)

Q: What bands and modes will give me voice at 3,000 miles? Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q), phone (Prev Q) (Next Q) I pursued Amateur Radio primarily for local emergency communications and as part of

my electronics education. My only radio right now is an inexpensive 2m/70cm HT which is good for local weather spotting and emergency operations. I’m interested in talking to other Amateur Radio users around the US, but I’m trying to keep my costs down. I know that many amateurs can make contacts worldwide on various bands at very low power levels, but many of them require specific conditions. I’d like to be able to talk with others around the US regardless of the conditions. What bands and modes best suit these requirements, in order of importance: USA Amateur Radio bands Voice contacts Long distance (3,000 miles, 4,800km, or more) Unconditional access (don’t want to worry about time of day, minor weather effects, etc) Low cost of setup (including antenna cost) Low power usage Small footprint (doesn’t require acres of antennas) The first four are critical. If there is no band or mode at any cost that fits these needs, then the question cannot be answered. If multiple solutions exist for the first four, then narrow them down or rank them according to each of the next three requirements. For instance a lower cost with a bigger antenna footprint would be preferable to a solution that cost more but had a smaller antenna footprint. Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q), phone (Prev Q) (Next Q) User: adam-davis Answer

by pearsonartphoto

You are going to have a very difficult time achieving the first 4 with any band on a low budget. But in general, I’ll say a few words to get you started. 1. You probably want to be able to use digital modes. Your best bet to get consistently across the country will be via digital modes, as they can add something like 20-30 dB effectively to your signal. Olivia in particular might be a good choice. This is achieved because digital modes are more sensitive, able to read signals below the noise floor. 2. If you want to be able to reach your “neighborhood” consistently, and occasionally around the world, then your best bet is probably 40 m. In fact, 40m is a highly recommended band to start out on. It works very reliably up to about 700 miles during the day, a bit further at night, and if you get it high enough, can work really well at night. Plus it’s less crowded and generally more friendly than 20m. 3. 20m is the best band overall to work around the world, but you often will have difficulties with things that are closer. 4. If you really want voice to anywhere in the world, you’ll want a huge yagi antenna on a large tower, transmitting at the full legal power in a quiet RF area. Other than that, you will have some compromise.

My set up is a G5RV in my attic, which I can talk routinely to Europe on 20m, most of the East part of North America on 40m, and occasionally further on 10 and 15m. I live in Virginia (FM19), to give you an idea. Answer

by scruffy

Based on the parameters given I would say 20M is the best band to aim for. There’s usually a lot of activity, it tends to give reliable propagation, your antenna can be relatively small and there’s a little bit of everything happening on it (CW, voice, digital and SSTV). From south-central Canada I’ve worked as far south as Cuba and as far east as Germany on a horizontal dipole hanging about 3 meters (10 feet) off the ground and most of North America with a sloper hanging off a tree at the edge of a field. For straight distance it’s hard to beat digital or CW though, so it may be worth learning Morse Code or finding some software to encode/decode it for you on the fly. Answer

by walter-underwood-k6wru

For long range voice contacts that work all the time, day or night, you need a satellite phone. Especially if you are considering emergency use, that is your best bet. If you want to do the same thing on amateur bands, you need high power, high gain antennas for several bands, and several years of intensive practice. You could set up an Elecraft K-line station (500 Watts), plus a tower and a beam for maybe $10K. That is about the cheapest setup that satisfies your top four requirements. If you are OK with digital contacts instead of voice, things could be a lot cheaper. It is common to talk cross-country with 10 Watts and simple antennas on digital modes. Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q), phone (Prev Q) (Next Q)

Q: How do sunspot numbers (SSN) affect radio operations? Tags: propagation (Prev Q) (Next Q), sunspots (Next Q) I frequently hear talk about SSNs in Amateur Radio, and somehow if the number is high, that’s a good thing. I just don’t really understand what they are, and what they mean, and I’d like to better understand them. What is the big deal about SSNs, what does it mean when they are high and low, etc? Tags: propagation (Prev Q) (Next Q), sunspots (Next Q) User: pearsonartphoto Answer

by dan

It refers to ‘smoothed’ sunspot number, and is needed by many software utilities to calculate optimal propagation. This refers to the current number of dark spots on the sun associated with high magnetic activity. When the number is high, the whole HF range up to 30 MHz can be used usually around the clock and F2 propagation up to 50 MHz is

observed frequently depending upon daily solar flux 10.7cm radiation values. During solar minima, or minimum sunspot counts down to zero, propagation of frequencies above 15 MHz is generally unavailable. In other words, high levels of sunspot activity lead to better signal propagation on HF bands, although they also increase the levels of solar noise and ionospheric disturbances (caused by impact of the increased level of solar radiation on the ionosphere). Answer

by k7aay

Sunspots correlate with a higher solar wind, which when it hits the ionosphere, makes the F layer more reflective to HF frequencies. So, hams can bounce signals more effectively when the SSN is high and reach further with their signals. Tags: propagation (Prev Q) (Next Q), sunspots (Next Q)

Q: Does modulation affect propagation? Tags: propagation (Prev Q) (Next Q), modes (Prev Q) (Next Q) Does the modulation scheme, whether OOK, SSB, AM, FM, a digital mode, etc, affect the propagation of a signal? Tags: propagation (Prev Q) (Next Q), modes (Prev Q) (Next Q) User: adam-davis Answer

by phil-frost

It depends on what you mean by propagation. If you mean, does the modulation scheme affect the physical means by which EM energy gets from point A to point B?, then the answer is no. Mostly, EM propagation is linear , so the differences in modulation have little effect on how the wave propagate. However, if you expand propagation to include the intelligibility of the signal at the other end, modulation can make a very big difference. Though propagation can practically be considered linear, it is not time-invariant . On VHF and UHF it’s common for the transmitter or receiver to be moving. At HF, the ionosphere constantly changes, significantly altering propagation. Across all the amateur frequencies, there are properties about the radio channel that vary with time. Different modulation schemes may be more or less robust against the disruptions encountered in practical RF channels. For example, the OFDM modulation used in codec2 provides good robustness against comb filtering caused by multipath propagation . It also provides forward error correction for additional robustness. This is why codec2 can offer many times the bandwidth of 300 baud FSK , while using less bandwidth, while working more reliability under more adverse conditions. The differences among analog modulation schemes are less complex, but they still exist. CW works well for communication under adverse conditions because all of the transmitter

power is focused in a very narrow carrier. On the other hand, AM spreads this same transmitter power over a wider bandwidth, and in that same bandwidth there is more noise the transmitter must overcome. Thus the principal advantage of SSB: it eliminates power wasted in the carrier and the 2nd sideband which carry no information. Furthermore, the wetware that decodes the baseband signal in analog modulation schemes is much better at detecting the pure tone of CW vs. the complex sound of a human voice in AM or SSB. Answer

by dan-kd2ee

Usually, the answer is no. While modulation may affect the acceptable Signal to Noise ratio, allowing a given signal to be received from further away or in worse conditions than a different modulation, that happens at the receiver, the propagation is the same. The only factors of a radio wave that affect propagation, once it’s in the air, are the field strength, frequency, and polarization. The only slight wrinkle in this that I can think of has to do with multipath distortion. Multipath distortion happens when signals are reflected by multiple surfaces and take more than one path from transmitter to receiever, of different lengths. Radio waves move at about 3 ∗ 108 m/s , so if one path is 35cm longer than another, and the radio wave is at 440MHz (with a 70cm wavelength), then they will arrive and cancel out perfectly. The modulation can affect this somewhat - but not by very much - simply because a CW signal has a much tighter bandwidth and is affected much more uniformly by multipath distortion than a very wide band (or even frequency-hopping) signal would. Tags: propagation (Prev Q) (Next Q), modes (Prev Q) (Next Q)

Q: Around the world propagation? Tags: propagation (Prev Q) (Next Q) Is it possible to transmit a signal around the world and receive it? Has anyone done it, and how? If not, how could this be accomplished? Assuming a complete path around the world, what kind of time delay should one expect on their transmission? Tags: propagation (Prev Q) (Next Q) User: adam-davis Answer

by phil-frost

It’s possible on HF (and below), and people have done it. It takes some combination of: high power transmitter sensitive receive antenna directional antenna(s) quiet RF location lucky propagation conditions In this case, the path is (roughly) any great circle around earth, so the distance is the Earth’s circumference. The signal moves at the speed of light, so we can ask Wolfram Alpha for “circumference of the Earth at the speed of light” and get 24901.47mi ≈ 134 milliseconds c Of course there are less spectacular ways to communicate around the world: store-and-forward amateur satellites linked VHF / UHF repeaters (example: EchoLink traffic nets


Tags: propagation (Prev Q) (Next Q)

Q: What are the general effects of a geomagnetic storm on propagation? Tags: propagation (Prev Q) (Next Q) Per NOAA/NWS Space Weather Prediction Center , “SWPC Forecasters are anticipating G3 (Strong) Geomagnetic Storm conditions to occur January 9 and 10.” What does that mean, very generally, for amateur radio communications? Does it depend on the type of geomagnetic storm and how it hits us exactly, or are there general effects we can predict? Does it increase or decrease propagation in all or some bands?

Tags: propagation (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

Geomagnetic storms are the result of solar events that subsequently impact earth’s ionosphere. They are graded from G1 (the mildest) to G5 (most severe) and the grade can be derived from the K-index (one of the many solar related values published NOAA ). A Kp index value of 5 equates to a G1 and a value of 9 equates to a G5. The predicted G3 storm for tomorrow is classified as a Strong storm by NOAA’s standards and is the result of a Coronal Mass Ejection (CME). CMEs are large clouds of plasma (ionized gases) that have been ejected from the surface of the sun. They are directional, and occur with some regularity, but are only a problem if the mass of particles heads our way. When they do head our way and impact the ionosphere, they cause a number of changes. Due to increased ionization of the lower levels of the ionosphere, signals between 2MHz and 30MHz will experienced increased absorption; if the storm is bad enough, that’s 100% absorption. Areas in the auroral zones are hardest it. During these storms they can experience rapid and deep signal fading due to the ionospheric irregularities that scatter the radio signal to the point that communication is impossible. On frequencies above 30MHz, unexpected reflections of the radio waves by the ionosphere may cause radio interference. Ionospheric irregularities may produce fluctuating signals (a phenomenon known as scintillation ) and may distort the paths of radio waves. If strong enough, this can adversely impact phase-sensitive systems on frequencies above 1 GHz (e.g., the Global Positioning System; talk about potential mayhem). Other effects include Auroral absorption, multipathing, and non-great-circle propagation. One possible happy effect (for those living in the mid and upper latitudes) is that the auroral zone moves equatorward giving folks who are not normally able to experience the aurora a chance to see them. And since propagation will be garbage, you may as well go outside and look. Other effects that could be important: some minor impact on the power grid by inducing some voltage fluctuations. Spacecraft may observe some surface charging on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems. Tags: propagation (Prev Q) (Next Q)

Q: How far can a 2.4 GHz, 1 watt signal go in a rural area? Tags: propagation (Prev Q) (Next Q)

What’s the approximate range achievable by a 2.4 GHz signal of 1 watt in semi-urban areas? I can see 2 km from our rooftop. Will a 2.4 GHz signal go that far, i.e. if I send WiFi signals from our rooftop is it possible to catch them on my phone 2 km away? Tags: propagation (Prev Q) (Next Q) User: user40713 Answer

by rory-alsop

This is a strange sort of question, as in reality the signal will go infinitely far (effectively) however you are really asking at what distance might a receiver be able to pick up the signal. In testing a 2.4GHz signal with a 100mW omni antenna, the furthest distance I could receive a signal with less than 5% retries (802.11b kit) was 2 miles with a 100mW 3dB receiver. I could manage over 5 miles with a directional 10dB antenna, but had some trouble aiming it accurately. Your phone is going to have challenges at that range, but if you have a specific location, you could use a directional antenna on your rooftop aimed at that location. Even a basic Huber Suhner running at 1W could make that work. (disclaimer - I used to test 2.4GHz radio kit from Symbol, Telxon, Motorola and Cisco. I can’t post the data tables, but more than happy to give indications of what might work) Answer

by adam-davis

It’s unlikely that the transceiver at the fixed location will hear the relatively tiny signal from your phone 2km away well enough to establish a link. You need to have more power on both sides to make it work. Even then, you might need specialized, large antennas or dishes. Of course if there are no restrictions then you should be able to establish such a link with huge dishes on either end at a fraction of that power. Tags: propagation (Prev Q) (Next Q)

Q: AM vs SSB weak signal Tags: propagation (Prev Q) (Next Q) I know single sideband is much better than FM for weak signal receiving. I know that SSB is just like AM, but with the unneeded parts removed. For weak signal propagation, like EME and aurora, would reception on AM or SSB be better? Tags: propagation (Prev Q) (Next Q) User: skyler-440


by wprecht–ab3ry

I don’t think anyone would be transmitting AM for weak signal work unless they were just fooling around. You’d get the same effect by cutting your power by 3/4s. In AM the carrier consumes 1/2 the power with the rest split between the side bands. So, SSB is not only more efficient use of spectrum, it’s more effective use of your power. Tags: propagation (Prev Q) (Next Q)

Q: Which HF bands are best during the day and which are better at night? Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q) I am rather new to HF operation and have recently purchased my first HF rig. I have read about bands being “open” and “closed” based on various conditions including time of day. As I have been listening, I have been bouncing around all the bands from 80 meters through 6 meters, but I am not sure which are better for me to try to make contacts on. I have heard that certain bands are more appropriate for daylight operation and others are better at night, but which are which? Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q) User: ghendricks Answer

by pearsonartphoto

In general, the shorter wavelength HF bands are better during the day, and the longer wavelength ones at night. Although that depends a bit on what you want to do, and like all things propagation, it’s subject to change. Let me try and give a rough mode of operations. Also take a look at the chart from eham . 6m- Randomly opened, in random directions. I think this happens more in the day, but I’m not a 6m expert. Strictly speaking this is VHF, not HF, but it’s often included on HF rigs. 10m- This is more consistently opened, especially in times of higher solar activity. Evening tends to be the best time, at least that’s what I’ve found, but this is a daytime band. 12-17m- These are traditional daytime bands, usually opened. The longer the band in this window, the more reliable it is, and the more likely it is opened night or day. 20m- Can be opened day or night. This is the most reliable band for dx. 40m- Daytime is opened in a “local” area, give or take 500 km or more with a good set up. Night time opened worldwide. 80m- Similar to 40, but even more extreme. 160m- This one is only opened at night, and tends to be a more local area. Not unlike 6 meters, strictly speaking this is MF rather than HF, but it’s often included on HF rigs.

Tags: propagation (Prev Q) (Next Q), hf (Prev Q) (Next Q)

Q: 2 m meteor scatter FM voice freq? Tags: propagation (Prev Q) (Next Q) What frequency should I use to try and make meteor scatter contacts on 2m FM tonight, with a nice meteor storm coming? Tags: propagation (Prev Q) (Next Q) User: pearsonartphoto Answer

by paul

There’s not a FM calling frequency for this sort of thing. FM requires good signals, and meteor scatter is very weak and intermittent when it exists at all. The meteor scatter crowd is mostly digital now. Most have all mode (SSB) radios hooked to their computer through some kind of sound card A/D interface and are using the free WSJT software written by Nobel prize winning physicist Joe Taylor K1JT. This software has esoteric modes that can deal with short lived paths or very weak signals in meteor scatter, and very weak slow signal modes for EME, and below the noise HF propagation. The messages exchanged are very short, typically only callsigns, R’s, or maybe a single number for a report. There is an online hangout for Meteor Scatter Enthusiasts at Ping Jockey


Tags: propagation (Prev Q) (Next Q)

Q: How do I make a RF propagation map for a repeater? Tags: propagation (Prev Q) (Next Q), repeater (Prev Q) (Next Q) Let’s say I have a repeater. Knowing all of the information about antenna height and gain in each direction, as well as power, how can I create a map similar to this map I saw of a repeater in Illinois?

Free options are always better! Tags: propagation (Prev Q) (Next Q), repeater (Prev Q) (Next Q) User: skyler-440 Answer

by adam-davis

SPLAT! is an RF Signal Propagation, Loss, And Terrain analysis tool for the electromagnetic spectrum between 20 MHz and 20 GHz. It is free and open source, and there are builds for Windows and Mac if you don’t want to compile from source on linux yourself. I haven’t used it, so I can’t speak to ease of use, but it should generate propagation maps based on elevation models and RF propagation characteristics. However it will probably not generate nice map imagery as above since it cannot integrate Google maps or a similar mapping source. Perhaps it can output KML files for use with Google Earth. Two groups have made free simple web interfaces for SPLAT!: (generates image and KML for Google Earth viewing) (??? Not responding at the moment) The image in your question was generated from CloudRF - a web service based largely on SPLAT!. CloudRF does have a web interface for generating such maps, and does have a free trial, which may meet your needs without installing and learning SPLAT!. Since CloudRF is built on SPLAT! and thus subject to the open source license SPLAT! was released under, the server backend is largely opensource . I believe the map shown was generated using the Keyhole Radio package, which is a client side helper that uses Google Earth along with the CloudRF servers to generate such maps from KML files generated by

CloudRF. Tags: propagation (Prev Q) (Next Q), repeater (Prev Q) (Next Q)

Q: Is free space path loss dependent on frequency? Tags: propagation (Prev Q) (Next Q), math (Prev Q) (Next Q) Free space path loss is calculated as: 4πdf ( ) c


The presence of f in this equation means that losses increase with increasing frequency, so there’s an inherent advantage in lower frequencies, right? Tags: propagation (Prev Q) (Next Q), math (Prev Q) (Next Q) User: phil-frost Answer

by phil-frost

Mathematically yes, the value of that equation increases with frequency. However, the free space path loss equation assumes unity gain antennas at each end. A larger antenna is required to get the same gain at a lower frequency. This larger antenna collects energy from a larger area. Thus, the frequency dependence of the free space path loss equation is due to our definition of gain, not space somehow attenuating higher frequencies more. In other words, if you halve the frequency, you must double the antenna size to maintain the same gain. The improvement you get in received power (by reducing f ) is the same improvement you’d get by maintaining the same frequency and doubling the antenna size (thus increasing antenna gain). To do a fair comparison, let’s compare two similarly sized antennas. Let’s compare a 2.4 GHz antenna with a 5 GHz antenna, each a parabolic dish antenna with a 5 meter reflector diameter. We can predict the gain of these antennas

with the the equation:

2 4πAf eA G= c2

where: A is the area of the reflector, f is the frequency, in Hz c is the speed of light in m/s, and eA is the aperture efficiency . If we assume an aperture efficiency of 80%, then: G 2.4GHz ≈ 41 dBi G 5GHz ≈ 47 dBi


G 5GHz ≈ 47 dBi In other words, despite these antennas being the same size, the 5 GHz antenna has about 6dB more gain. Does this compensate for the higher free space path loss at 5 GHz? Let’s do the math. The power received will be proportional to the antenna’s gain (from equation 1), multiplied by the reciprocal of the free space path loss (equation from the question): 4πAf ( c2 ⎛ 4π A f ⎜ c2 ⎝



c eA ) ( ) 4πdf


⎞ ⎛ ⎞ c2 eA ⎟ ⎜ ⎟ ⎠ ⎝ ( 4π d)(4πd) f 2 ⎠

A eA 4πd 2

Notice that this equation is just the area of the reflector and the aperture efficiency divided by the surface area of a sphere with radius d. In other words, irradiance decreases with distance in accordance with the inversesquare law , regardless of frequency. The presence of a frequency term in the usual free space path loss equation is merely an expression of the fact that lower frequency antennas of similar gain are physically bigger, and thus are subject to a greater radiant flux . It’s the increase in antenna size, not the decrease in frequency, that reduces the free space path loss. Tags: propagation (Prev Q) (Next Q), math (Prev Q) (Next Q)

Q: Can there be propagation of HF from satellites? Tags: propagation (Prev Q) (Next Q), satellites (Prev Q) (Next Q) HF transmissions from the ground can be reflected by the ionosphere leading to very long distance propagation. Satellites in low Earth orbit (160 km to 2,000 km) fly within the ionosphere (60 km to 1,000 km); with the F layer at 150 km to 500+ km. So if a satellite is under, over or in the F layer, do the signals get absorbed, reflected away from the earth, or skim around/under the ionosphere (i.e. propagate a long distance)? This would also depend on the incidence angle, presumably. The reason I ask is I am wondering if HF would be useful for in CubeSats, which at UHF frequencies can only downlink/load during short pass windows. HF would probably be a lower bandwidth connection, but the time available, and the more constant connection might outweigh the low bandwidth. Tags: propagation (Prev Q) (Next Q), satellites (Prev Q) (Next Q) User: darcythomas


by tomnexus

Satellites can and do use HF for communications. The first example would of course be Sputnik

, which transmitted at 20 and 40 MHz.

Amateurs use HF to communicate with satellites. According to Amsat


mode A: This mode requires a 2 meter SSB/CW transmitter and a 10 meter SSB/CW receiver… Mode K; This mode requires a 15 meter SSB/CW transmitter and a 10 meter SSB/CW receiver… This mode is unique in that it can be done with a simple HF rig. HF has advantages in its smaller Doppler shift, and reduced path loss, allowing omnidirectional antennas to be used more easily. For the physics part of your question: the reflection from a layer of the ionosphere depends on electron density, frequency and angle of incidence (which changes its effective thickness). At normal incidence, frequencies of below about 7-10 MHz are reflected, higher frequencies pass through. See Wikipedia for a graph of reflection against height. This page gives a great overview; (written with communication in mind, but what isn’t reflected is transmitted). The equation for MUF is F_normal / ( sec θ ). So it’s only for very long paths, grazing reflection, that the ionosphere ever reflects a 28 MHz signal. It would usually pass straight through the ionosphere, down to a fairly shallow angle. Your last question makes it sound like you hope to use HF from a cubesat when it’s over the horizon, not in line of sight. This would be highly unusual and would certainly not help with your data rate problem. 1. If you choose a frequency which easily penetrates the ionosphere, then it won’t bounce around inside, to get to you, it’ll just reflect out again. 2. Cubesats have very limited power, HF requires plenty of power to communicate around the world, 10s or 100s of watts. 3. If you’re trying to send more data during a pass, then the right solution is to go higher in frequency, where antenna gains are higher, there’s less atmospheric noise, and more bandwidth available. HF modems run at 1200 bps, WiFi runs at 11 Mbps and more. That all said, there is one tiny balloon project , launched to fly around the southern hemisphere, that uses HF to phone home. It’s only 30 km high, but it transmits just a few mW using wspr, and can be heard around the world, with luck. Bear in mind that it sends nothing but its position and callsign. Tags: propagation (Prev Q) (Next Q), satellites (Prev Q) (Next Q)

Q: Incoming angle of radio signal reflected off of ionosphere

Tags: propagation (Prev Q) I am about 870 miles and 16 degrees due west of WWVB at Ft. Collins, CO. WWVB transmits at a frequency of 60 KHz. At this distance I should be getting the signal reflected from the ionosphere. If I assume the ionosphere layer I’m getting the bounce off of is sixty-two miles high and it’s a straight line between here and WWVB, using Tangent = Opposite÷Adjacent (T=62÷435), I get an incoming angle of 8.1°. Since I’m 16° away, I’m tilted 8° away from the midpoint between here and WWVB, which gives me an incoming angle of only 0.1°. This seems counterintuitive. The reason I ask this is because I have a so-called atomic clock on my kitchen counter that does not get a signal unless I move it away from the solid patio cover next to the kitchen, but since the signal is at such a low angle, the patio cover shouldn’t matter. I only need to move it a few feet for it to get a signal. So is my math right, or am I missing something? Edit: I’m not sure where I got the 62-mile figure, but a Wikipedia article I found and a PDF state the altitude of the F Layer starts at 93 miles. With that figure plugged into the formula, it gives me an incoming angle of slightly more than 4°, which is probably just enough (can’t measure it precisely) for the patio cover to come into play. Tags: propagation (Prev Q) User: billoer Answer

by hamsterdave

Calculating the angle of an incoming signal traveling via skywave is not nearly so straight forward as you might presume, and there are two primary reasons. The ionosphere is highly variable, and also exists not as a single impermeable layer, but rather a diffuse region several hundred kilometers thick. At any given moment, two signals of significantly different frequency will likely appear to ‘bounce’ from two very different altitudes depending on ionospheric conditions, transmitter antenna characteristics, and frequency of the waves. The height at which the signal appears to reflect is referred to as the “virtual height”. In reality, the signal is refracting over a relatively large physical distance, gradually bending back toward earth as it moves through the ionosphere. The distance over which the refraction takes place is dependent primarily on frequency, with higher frequency requiring a longer path. This means that if you have a 10MHz and a 20MHz transmitter with identical antennas, the 20MHz signal will have a longer single hop range, so long as the maximum usable frequency at the point where your signal meets the ionosphere is greater than 20MHz. Things are further complicated by the highly variable nature of the ionosphere. Depending on time of day, solar conditions, and the state of the earth’s magnetic field, the varying layers of the ionosphere can not only change altitude by more than 50% over the course of a single day , but they can even merge with other layers, or almost disappear completely.

The F1 and F2 layers merge during local night to form a single layer, and the D and E layers are dramatically weaker or almost absent, for example. The F1 layer might begin at 150km at 10am today, but it could start somewhere above 200km at 10am tomorrow. The exact range of a single hop also depends on takeoff angle from the transmitting station, as a wave with a frequency of 5MHz for example, is likely to return to the earth even if radiated nearly straight up, just as it would if it were radiated at 4 degrees above the horizon. Waves can also make multiple trips between the surface and the ionsphere, and there are times when two short hops can result in good reception, while a single longer hop may not. In your case, you are well within range of ground wave propagation (nearly the entire continental US is for at least part of the day). At 60KHz, and a whopping 70kW ERP, the night time ground wave range is >1,000 miles. Skywave propagation on VLF is finicky stuff. The ionosphere and the surface of the earth can form a waveguide that a VLF signal propagates along quite well, but this can vary depending on time of day and ionospheric conditions, as sometimes the altitude of the layers is not optimal for a particular frequency. Lastly, if this were indeed a case of skywave ‘shadowing’ from a porch awning or other object in your home, the size of the shadow would depend on the electrical size of the object that’s creating it to the wave that it’s blocking. In the case of a 60kHz wave, an object would have to be absolutely enormous to create appreciable attenuation, as the wavelength is almost exactly 3 miles long. That means significant shadowing might require an object to be several hundred feet along at least one axis. By comparison, the low end of AM broadcast at 500kHz is about 1 mile, and FM radio at 100MHz is just 3 meters. Moving the object just a foot or two and seeing marked improvement, as you describe in the comments above, all but rules out skywave shadowing on this frequency. It is far more likely that you’ve got an issue with local radiated or coupled interference that’s rendering your WWVB receiver deaf. Tags: propagation (Prev Q)

HF Questions Q: What is generally considered “too much” power for JT-65 on HF? Tags: hf (Prev Q) (Next Q), digital (Prev Q) (Next Q) Recently, I have begun experimenting with JT-65A, mostly on 20 meters. I usually run about 5 watts with that mode, since I know that JT-65 is a weak-signal mode. Is that still too much power? What is generally considered excessive power on JT-65? Tags: hf (Prev Q) (Next Q), digital (Prev Q) (Next Q) User: krzysz00-kf5soq Answer

by dan-kd2ee

5 watts is probably what most JT-65 purists will tell you to use, but in practice, I tend to aim for 20 watts. That gives you a good 6dB boost (every doubling of power is equal to +3dB) which is actually meaningful in JT-65. Any more than that, and you’ll start finding certain problems. Note that the same is true for the WSPR family of protocols. First, that since everyone else is using less power than you are, you’ll have many cases of people hearing you, but you can’t hear them. That in turn means that you run the risk of interfering with a conversation that you can’t even see, especially if you’re running 100W and they’re each at 5 or 20. Finally, many transceivers will cause distortions in the JT-65 waveform when run at above a quarter to a half of their maximum power. Transceivers are meant to work with analog data, not the sharp frequency transitions of the digital signal. Overdriving them can cause clipping, which will cause you to actually waste power and may even make your transmission unreadable. So to answer the question, the standard maximum is either 20 or 30 watts - and there’s really no point in exceeding that. Many people win awards on the mode at 5 watts! Most transceivers will distort your waveform above a certain limit, and there’s no point in risking it for another 2 or 3 dB. Answer

by james-nf8i

As you stated, JT-65 is a weak signal mode. This should not be confused with a low power mode. Depending on your antenna and location, the amount of power you need to conduct a successful contact may vary, just as in any other mode. A good guideline would be to start at the lowest power setting you can, and if you’re not able to work the stations you want (and can hear!), gradually increase power. If possible, use some of the online spotting networks ( or ) to see

what signal reports you are getting. If you are being received anywhere between -10 dB and -20 dB, you’ve nailed it! If you are consistently getting numbers between -10 dB and 0 dB, you can reduce power. If you aren’t being heard or you get numbers below -20 dB, try increasing power. I’ve worked stations using milliwatts who were booming in for me, and I’ve worked at least one station who claimed to be running 1 kilowatt. The kilowatt guy got a -10 dB report from me, so I guess he wasn’t using too much power! Good luck and 73! Tags: hf (Prev Q) (Next Q), digital (Prev Q) (Next Q)

Q: How to reduce RF in the shack when using vertical HF antenna (no radials) Tags: hf (Prev Q) (Next Q), rfi (Prev Q) (Next Q) What can be done to reduce RF in the shack (riding back along the coax) when using a vertical 10M antenna (without radials due to space constraints)? The antenna is an IMax2000 at 32’ elevation (20’ over roof) with a 125’ coax LMR-400, SWR is under 1.5 across 10M band. No balun, no tuner. Cable length is required to reach the shack room (basement). Max power 100 W with interference level increasing with greater power output. This is causing interference with capacitive touch lamps (on, off on transmit); as well as causing speakers around the house (even when turned off) to broadcast the operator’s voice (a ghoulish combination with the flickering lights). The height of the mast was adjusted from 1’ to its present 32’ over ground level, with no change to SWR or interference as described above. The mast was tried with and without grounding (to an 8’ ground rod at its base), no effect to SWR or interference level. Tags: hf (Prev Q) (Next Q), rfi (Prev Q) (Next Q) User: ron-j.-kd2eqs Answer

by phil-frost

You may be surprised to hear this, but the antenna you describe isn’t actually a vertical, but a dipole. One half of the dipole is the IMax-2000, and the other half is your feedline. You can not simply not have radials and still have an antenna. An antenna works by making EM fields between two things. A dipole has two halves. A vertical works because the ground plane under it creates an image antenna under it, making it appear as a dipole. To get the RF currents off of the feedline, you have to give it some other place to go. You could: install a dipole

install elevated radials mount the vertical on the ground You can also put a high impedance on the feedline to make that path less desirable to RF currents. An easy and effective way to do this is to slip ferrite beads over the coax. However, if you don’t first provide a more desirable place for them to go, then you are just putting ferrite beads on your antenna, which will reduce the RF in the shack, and also everywhere else. I would also point out that a SWR of 1.5:1 does not in itself indicate that the antenna is working well. SWR only indicates that that the antenna is decently matched to the feedline, and thus accepting (and not reflecting) power: it doesn’t indicate that the power accepted is actually being radiated as intended. One way to make an antenna get a good match across a wide band is to make it very lossy. As an extreme example, I have a dummy load that has a 1:1 SWR from DC up to beyond the capability of my test equipment. Answer

by ron-j.-kd2eqs

(a partial self-answer) Bad grounding on the mast was part of the problem. After reconnecting the ground wire to ensure a clean contact on both mast end and ground rod - the blinking lights stopped. The RF return was almost eliminated (slight deflection on FS meter against coax but I think that is to be expected). Per Phil Frost’s answer, I believe the shack ground was providing a better RF ground since the mast was improperly grounded, causing the RF to ride back indoors. Once connections were sandpapered and tightened to the outside grounding rod, it took the shorter route to ground. Update after getting my General and attempting to go beyond the 10m band with this vertical antenna. Testing SWR on 12m (SWR 1:2) and 17m (SWR 1:3) both resulted in the same common current RF problem - and the lights getting turned on and off. Will update again after I try using an antenna tuner. Tags: hf (Prev Q) (Next Q), rfi (Prev Q) (Next Q)

Q: How are multiple-operator contest stations with one radio usually operated? Tags: hf (Prev Q) (Next Q), contest (Next Q) I am the president of a small school club. We plan an participating in the ARRL SSB Sweepstakes this weekend, which is our (new) club’s first real multi-op contest effort. How do multioperator/club contest stations with only one transceiver usually operate? Is it common practice to have one person handling the radio while having another logs? I was thinking of setting up some parts of the contest up like that.

Tags: hf (Prev Q) (Next Q), contest (Next Q) User: krzysz00-kf5soq Answer

by w5vo

My advice won’t necessarily be good for a competitive score, but here is what I’ve found from running a school Club station during Sweepstakes. The main thing is to have fun! Don’t take it too seriously if it’s your (or anyone that’s operating) first time contesting. For running multi op, it really depends on how many people you have and their experience level and time availability. If you have people who are completely new, then it usually helps to have two pairs of ears listening with one person operating while the other logs the contacts. Two people at the radio means that there is a double check on the exchange, and that it’s easy to swap positions for a break. That being said, it isn’t that hard to log and operate at the same time. I prefer working alone, and use the multi op to avoid spending a whole day in the station. Tags: hf (Prev Q) (Next Q), contest (Next Q)

Q: How can I generate a list of APRS IGates on 30m? Tags: hf (Prev Q) (Next Q), digital (Prev Q) (Next Q), packet (Next Q) I am investigating using a Tiny Trak 4 with my portable HF radio to self-spot on SOTA activations via APRS on 30m. I usually self-spot via a text message. When I don’t have any cell coverage, I can sometimes spot using APRS on 2m. I am looking for a solution for relatively remote areas where I don’t have any cell coverage and don’t have any 2m digipeater coverage. If I can get APRS messages out on 30m that would do the job. I can find references on the Internet to using APRS on 30m, but I don’t find any information on where or how many 30m IGates there are or what the coverage is. How can I generate or where can I find a list of APRS igates on 30m? Tags: hf (Prev Q) (Next Q), digital (Prev Q) (Next Q), packet (Next Q) User: malcolm-ve2ddz Answer

by adam-davis

The APRS system and protocol itself doesn’t track iGate type or frequency. There is a list of active iGates, but there is no frequency information for them, or for the packets they receive. Further no one appears to maintain a database of such stations.

However those that have used it indicate that the coverage is good enough that you really don’t need to worry about coverage. Depending on the propagation you will almost always make it to an iGate regardless of your position on any of the continents. However, it should be easy to generate such a list yourself over time. Start broadcasting APRS packets on HF and watch APRS-IS feeds for your packets. You should be able to determine what iGate passed them to the internet, and you can then find out the location of that iGate from its own APRS packets. This will have to be done slowly over time as propagation changes, and to avoid preventing others from using the band. Note that in order to make packets as small as possible, repeating stations strip some information from the packet as they repeat it. This information would tell you what station(s) your packet has already gone through - in other words, your generated list of iGates will only show those iGates that actually placed your packet on the internet, not any inbetween that have repeated it. Further, some HF igates may not be directly connected to the internet, thus you might find a packet gets received on HF, repeated on 2M, then received by a 2M iGate connected to the internet. You’d see the last repeater in the packet on the internet, however since 2M is generally short-haul, it’s likely that even if some packets are repeated via radios before hitting the internet you’ll still get a good idea of the position of the actual HF receiver, since you’re most likely interested in general regional positions of HF APRS gateways and repeaters. Tags: hf (Prev Q) (Next Q), digital (Prev Q) (Next Q), packet (Next Q)

Q: Why do we use LSB below 10Mhz and USB above 10Mhz when operating SSB HF? Tags: hf (Prev Q) (Next Q) As a relatively new ham operator, I understand that it is customary to use lower-sideband below 10Mhz and upper-side band above 10Mhz when operating single-sideband HF. I’m curious how we got to such a standard instead of just picking one or the other for all bands. To further complicate it for new hams, it seems that RTTY operators use lower-sideband everywhere and PSK operators use upper-sideband everywhere. (Reference ) Is there any technical reason not to use upper-sideband everywhere? Or is this purely tradition to be passed on for the sake of tradition? Does anyone know some verifiable history for how this de-facto standard came to be? Tags: hf (Prev Q) (Next Q) User: benswayne Answer

by adam-davis

Amateur Radio operators use this rule of thumb for historical technical reasons. SM0AOM on the QRZ forums writes : The changing of ISB sideband positions at 10 MHz actually has an engineering background. In the earliest ISB exciters, it was found appropriate to change the final mixer scheme from subtraction to addition mixing at around 10 MHz due to spurious suppression concerns. This sometimes caused interoperability problems in international point-topoint ISB circuits. To overcome this, a practice was formalized in 1959 by the ITU/CCIR as the Recommendation 249, which prescribed that the ISB sideband positions could either automatically or manually be interchanged when the output frequency went through 10 MHz. An often quoted reference where ISB exciter design considerations are handled with German thoroughness is W Kleische: “Fernbedienbarer Steuervorsatz für Kurzwellen-Nachrichtensender” in “Telefunken-Zeitung” December 1962. Later advances in exciter design made this Recommendation obsolete, and later generations of exciters only had this facility as an option, and current production ISB equipment lacks it entirely. Tags: hf (Prev Q) (Next Q)

Q: Why are commercial SDRs so limited in operating frequency?

Tags: hf (Prev Q) (Next Q), software-defined-radio (Next Q), transceiver (Next Q) I spent a bit of time researching SDRs, mostly looking into the possibility of building an all-FPGA-based TRX. There are a lot of commercial ready solutions; some are cheap, some not, but they all tend to be operating from 50/70 MHz frequency range. I am a complete newbie in RF processing and what escapes me is: if the circuitry is able to process a 50 MHz signal, why can’t it do the same with lower frequencies? Is it some physics limitation? I guess it must be — otherwise everyone would advertise an operatiing range from DC to X MHz. Or is operating on lower frequencies uninteresting to everybody except hams? My question is TRX specific — not RX only. Tags: hf (Prev Q) (Next Q), software-defined-radio (Next Q), transceiver (Next Q) User: ulterior Answer

by phil-frost

Largely it has to do with filtering and bandwidth. An ADC requires an anti-aliasing filter to remove all input frequency components that are more than half the sample rate. Otherwise, these higher frequency components get aliased onto lower harmonics. As an example, if I have a 40 kHz ADC, it should be able to handle at its input anything from 0 to 20 kHz. If I should feed it 25 kHz, it will appear as 15 kHz…not what you want in a radio. The anti-aliasing filter removes everything above 20 kHz so this does not happen. If I have that same 40 kHz ADC, but I want to handle radio frequencies above 20 kHz, I need to introduce a mixer . This is a device that shifts one band of frequencies to another. So, if I want to work in the 40 meter band, I need a mixer that converts frequencies around 7 MHz down to 0 - 20 kHz for my ADC. However, my mixer will again require filters to avoid intermodulation and aliasing. All of this is equally applicable to transmitting — the process is identical, except in the other direction. However, some stages of the transmitter must handle high power, which makes the filters larger and more costly. This is why it can seem easier to find a receiver with coverage of more bands. So greatly simplified, the coverage of an SDR, or in fact, any radio, is determined by what filters it includes. As an example, take a look at the SoftRock RX Ensemble , which includes filters for four bands, and by changing the component values, can be built to cover LF or HF. With a sufficient selection of filters it becomes possible to cover the entire RF spectrum, but this would be expensive. Tags: hf (Prev Q) (Next Q), software-defined-radio (Next Q), transceiver (Next Q)

Q: How does selecting the opposite sideband when receiving CW on HF reduce interference?

Tags: hf (Prev Q) (Next Q), cw (Prev Q) (Next Q) I am studying for my FCC General Class license, and question/answer G4A02 reads as follows: Q: What is one advantage of selecting the opposite or “reverse” sideband when receiving CW signals on a typical HF transceiver? A: It may be possible to reduce or eliminate interference from other signals. I am studying from the ARRL General Class License Manual (Seventh Edition). I don’t understand how this is possible. If the signal is being transmitted on the upper sideband, how does switching to receive on the lower sideband eliminate interference? As I understand it, that would eliminate everything from the upper sideband, and I would hear nothing from the upper sideband including the CW signal I’m trying to listen for. The referenced page from the Q/A explains this concept thusly: … Reverse Sideband controls allow the operator to switch between receiving CW signals above the displayed carrier frequency (USB) and below it (LSB). This can help avoid nearby signals causing interference by placing them on the other side of the carrier frequency where filtering rejects them. … I do not understand. How does this work? Tags: hf (Prev Q) (Next Q), cw (Prev Q) (Next Q) User: bryson Answer

by kevin-reid-ag6yo

CW signals are not “transmitted on the upper sideband”, nor the lower one. A CW signal is approximately at a single frequency (with only the additional bandwidth required to allow the key-up and key-down transitions). However, the standard method of receiving a CW signal is identical in structure to a single-sideband receiver. The local oscillator (LO) of the receiver is set to a frequency not quite equal to the CW signal, and the difference between the incoming CW and the LO is the audio tone you hear. Let’s say for concreteness that the difference is 800 Hz. If that frequency shifting were all that was going on, then you would hear many CW signals (from both sidebands) at different pitches, so there is a very narrow filter to select just the one signal. That filter will select either the frequency +800 Hz from the LO (upper sideband) or the one −800 Hz from the LO (lower sideband). For convenience, a modern transceiver does not display the LO frequency (as it does in single-sideband mode) but rather the LO frequency offset by 800 Hz, so that you know the actual frequency of the signal. If you switch from upper-sideband reception to lower-sideband reception, then you (or

your receiver’s CPU, more likely) should simultaneously change the LO frequency to be 1600 Hz (double the offset) higher, so that (if you were perfectly tuned to start with) you’ll hear the same signal at the same pitch as before. The difference this makes is that signals not exactly at the 800 Hz offset frequency will be flipped around that midpoint: an unwanted signal within the filter passband that was at (relative) 1200 Hz will now be at 400 Hz, and you might find that lower-pitched sound less troublesome. Or, if your receiver’s filters are not perfectly symmetrical for this purpose, the unwanted signal could be actually attenuated. If you have a receiver already, listen to CW and SSB signals using both CW and SSB modes, tune around, and try to get a feel for what’s going on. CW mode is just SSB mode with a narrower filter and the offset display. (Note that when you switch between CW and SSB mode, your receiver might preserve the actual LO frequency (thus changing the displayed frequency), or preserve the displayed frequency (thus changing the LO frequency and the pitch of what you hear). Tags: hf (Prev Q) (Next Q), cw (Prev Q) (Next Q)

Q: Why do I only hear broadcasts from 150 kHz to 29.999 MHz? Tags: hf (Prev Q), receiver (Prev Q) (Next Q) I am currently studying for my amateur radio license. Until I’m licensed, I’m trying to use a Sony ICF-SW7600GR receiver to listen in on amateur radio “phone” transmissions. No matter what I do, however, I can’t seem to locate any amateur radio conversations. Everything I manage to tune into is a broadcast, usually some news, music, or religious broadcasts. Since this receiver covers all MF and HF amateur bands, I really expected to pick up something. I’ve dialed directly into frequencies set aside for “phone” in Region 1 (I’m in Prague, Czech Republic), searched LSB under 10 MHz, USB above 10 MHz, normal AM, utilized the external SW antenna, dialed in directly to local stations, tried with and without synchronous detection, etc. Maybe everyone is using FM or PM while my receiver only picks up AM? Tags: hf (Prev Q), receiver (Prev Q) (Next Q) User: rcampbell Answer

by kevin-reid-ag6yo

It doesn’t sound like you’re doing anything wrong. Most likely, you are simply only hearing strong stations; broadcasters put much more power into their transmissions than amateurs are legally allowed to, so you can hear them over a much wider range. Advice on the practice of listening: For finding signals, first of all, always use SSB. Even if it’s the wrong mode to demodulate the signal correctly, you will hear something (often including a strong

carrier tone), because SSB is just turning a slice of the RF spectrum into audio regardless of what it contains. The only way you can miss hearing a signal using SSB is if the signal is much wider bandwidth than 3 kHz (so that it sounds like just an increase in the noise floor). Once you have found something, you can try other modes to receive it correctly. Try tuning to the CW band segments (using a CW mode if you have it, otherwise SSB), rather than phone. Even if you don’t know Morse code, CW signals are much easier to pick out of the noise by ear, so you can tell whether you’re receiving anything. Make sure you’re listening at the right time. Broadly speaking, propagation is better at night, so not only will you receive better, but more people will be transmitting. You should be able to hear the broadcasters more clearly as well. When you’re studying for your license, read about the ionosphere and other kinds of propagation effects, and figure out when you should be listening to what band. Advice on improving your reception: You may have local noise sources which interfere with reception. They won’t necessarily sound like anything other than the usual hiss of noise. Shut off all the electrical devices in your home temporarily and see whether they make a difference. (Instead of listening for signals you can’t hear yet, listen for how clear the broadcasters are.) Or, especially if you’re in an apartment building with many close neighbors, you could try going out to a park or other location with very little electronics. Make sure you have a decent antenna. Since you are receiving, not transmitting, this is not critical, but it helps. According to some reviews, your model of radio comes with a reel of wire in addition to the telescoping antenna; use it. There are two basic approaches: “Long wire”: Make your antenna wire as long as you can reasonably fit in the space you have. (Keep it away from large metal objects.) Make it resonant on the band of interest. In particular, make it about 1/4 wavelength long, or possibly an odd multiple (3/4, 5/4, and so on). (Coiling up the free end will make it effectively shorter without needing to cut the wire.) Maybe everyone is using FM or PM while my receiver only picks up AM? Nobody uses FM on HF, because it is a waste of bandwidth. But if they did, then you could still hear it. Specifically: An AM receiver tuned exactly on a FM signal will produce silence (not noise). An AM receiver tuned slightly off the FM signal will produce decent audio, with excess noise. A SSB receiver tuned to an FM signal will produce a distorted sound which will still be recognizable as being voice-like (due to the timing of speech sounds), and possibly a tone from the carrier.

Tags: hf (Prev Q), receiver (Prev Q) (Next Q)

License Questions Q: What is the procedure to obtain an amateur radio licence in Australia? Tags: license (Prev Q) (Next Q) What and how would I go about obtaining a licence for HAM radio in Australia? Do the licencing regulations vary significantly from state to state? Tags: license (Prev Q) (Next Q) User: user17 Answer

by pearsonartphoto

From the Wireless Institute of Australia , to get one of the 3 license classes, you have to take an assessment. The assessment covers various amateur radio related topics, each level increasing the difficulty and depth of knowledge required to operate. They are set at the country level, thus there is no difference between states. To figure out where to take the test, take a look at the WIA’s list of assessors Tags: license (Prev Q) (Next Q)


Q: Would I still be a valid volunteer examiner? Tags: license (Prev Q), arrl (Prev Q) (Next Q) I’m currently an ARRL member, and a volunteer examiner under the ARRL/VEC. I find myself needing to cut back on expenses this year and may end up dropping the ARRL membership. If I do so, am I still a valid examiner under the ARRL/VEC? If so, will I also be able to renew with ARRL/VEC when my renewal date comes up? Tags: license (Prev Q), arrl (Prev Q) (Next Q) User: brian-knoblauch Answer

by adam-davis

According to the current Volunteer Examiner manual from ARRL , you can meet the requirements without becoming an ARRL member, and your VE status is only affected by your license status: As a Volunteer Examiner (VE), you are the gatekeeper to the integrity of the Volunteer Examiner Program. To that end, you must have certain qualifications and be accredited by a Volunteer Examiner Coordinator. To qualify to be a Volunteer Examiner, you must: be 18 years of age or older; and never have had your amateur station or operator licenses suspended or revoked; and hold a valid General, Advanced or Extra Class license.[97.509] If you meet these criteria, the ARRL/VEC would like to hear from you. To be accredited by the ARRL/VEC, you must complete a training program. Examiners may be accredited by more than one VEC. VEs are not required to work with only one VE Team or VEC and are not restricted to any particular area. A VEC does not have to accept the services of a VE if it does not want to. Further, even if there were such a requirement to become one, it doesn’t expire on any other basis except that of your FCC license: Once accredited as an examiner in the ARRL/VEC’s program, your accreditation credentials will be good until your FCC license expires. Your accreditation is valid at any ARRL/VEC coordinated session. I expect that as it is a voluntary position through the FCC granted by an act of congress, they can’t make membership in their organization a requirement to be accredited by them. You can be accredited by another VEC , though, if the ARRL terms don’t meet your needs.

Tags: license (Prev Q), arrl (Prev Q) (Next Q)

Modes Skip to questions, Wiki by user wprecht–ab3ry Questions related directly to the mode of communication (SSB, CW, digital, etc).

Questions Q: Why is Morse Code still in use? Tags: modes (Prev Q) (Next Q), cw (Prev Q) (Next Q) Why do people still use Morse Code? What are its advantages over newer Voice or Data communication modes? Tags: modes (Prev Q) (Next Q), cw (Prev Q) (Next Q) User: timtech Answer

by scruss

because there are a large number of operators who had to learn it to get their licence. because there is a large (but slowly diminishing) number of operators who learned it while serving in the armed forces. because the transmitters and receivers can be extremely simple and inexpensive , not needing much more than a key and headphones along with the rig, antenna and battery to send and receive. because (in theory) it has a very tiny bandwidth, allowing small QRP transmitters to send a very effective signal. This also allows a large number of contesters to cram into a few kilohertz of bandwidth, each (with suitable filtering) able to be picked out individually. because it’s a point of pride for some operators that they know this thing that the young ‘uns don’t. CW can be sent exceptionally well by computer (with software like fldigi ) or by any number of USB/serial keyers (such as the WinKeyer or K3NG Arduino keyer). It can be copied reasonably well in software (fldigi again, or CW Skimmer ). The Reverse Beacon Network relies on multiple stations worldwide running CW Skimmer to report on propagation, and will show you where your CQ has been copied. It can be thought of as a digital mode, but one that can be copied by ear with sufficient training. It’s typically a little slower that PSK-31 or RTTY, and CW only supports a very limited single-case character set. Although it is no longer used commercially or by the military, it’s likely to stick around in ham radio for a long time. Answer

by evan-fosmark

The advantage? Efficiency! You get to put all of that power of your rig into a very small bandwidth, whereas voice modes need to spread the power out much more (for example, SSB uses roughly 2.8kHz of bandwidth). Quote from:


Going a little bit further, assuming a SSB signal takes up 2000 Hz., and comparing a 100 watt 25 WPM CW signal with a 100 watt SSB signal, we have the following.

The average power density for CW is 100W / 100 Hz. or 1 w/Hz. For SSB it’s 100W / 2000 Hz. or .05 w/Hz. Follow closely now, it gets interesting although a little more technical. We could say that the gain in using CW over SSB is Gain(db) = 10*log(1/.05) which is about 13db. That means that a 5 watt CW signal packs an equivalent punch to a SSB signal at 100 watts. Answer

by nc4pk

One of the reasons it’s still in use is because of its inherent simplicity - no real signal processing is needed. Thus, CW transmitters and receivers are very simple and thus inexpensive. Tags: modes (Prev Q) (Next Q), cw (Prev Q) (Next Q)

Q: What is the role of digital data modes in emergency communications? Tags: modes (Prev Q) (Next Q), digital (Prev Q) (Next Q), emergency (Next Q) Emergency operations are typically reliant on voice traffic today. Are digital data modes used at all in emergency operations, and why/ why not? Couldn’t data modes be used to pass information more efficiently than voice? Tags: modes (Prev Q) (Next Q), digital (Prev Q) (Next Q), emergency (Next Q) User: jc-hulce Answer

by k7aay

In the US, disaster declarations need to be approved and that declaration with approval must be transmitted to a state EOC before state aid can be approved. Therefore, early in the game, packet has become popular to get that declaration to the state capital. Although HIPPA does not apply to amateur radio (as operators are not healthcare providers), there’s still a great desire not to reveal names and other details of aid recipients. Packet and other modes provide ‘security through obscurity’ and are more popular in sending long lists of data. Some places need to survey vulnerable infrastructure, and a ham with digital camera capability can deliver pictures back to where the Internet works so engineers can look at, say, a dam face, or a bridge support. Just had an exercise last month where hams on mountain bikes were asked to offroad and do that. explains how D-STAR was used in 2007 to improve comms in severe flooding in Western Oregon, about 30 klicks from where I sit. There are more examples, but those are the three big ones which come to mind based on my experience with ARES and ARC in disaster.

Tags: modes (Prev Q) (Next Q), digital (Prev Q) (Next Q), emergency (Next Q)

Q: Is it possible for an amateur to transmit ATSC? Tags: modes (Prev Q) (Next Q), digital (Prev Q) (Next Q) Amateur television has long used the NTSC (analog) television standards to transmit video and audio. Several years ago, the digital broadcast television transition made higherquality television signals possible. Can amateurs acquire and use digital television (ATSC or DVB) transmission equipment? Tags: modes (Prev Q) (Next Q), digital (Prev Q) (Next Q) User: jc-hulce Answer

by k7aay

FCC Regulations, Title 97.307(f)(8) says yes, you can transmit with ATSC modulation in the US, BUT you can’t use frequencies which match US ATSC channels. You would need to find a receiver (maybe PC controlled?) flexible enough to listen to amateur frequencies. As to DVB-T or DVD-S, well, they’ll work with about 2MHz of bandwidth instead of the 6MHz slice required for ATSC. Again, a flexible receiver is called for. Tags: modes (Prev Q) (Next Q), digital (Prev Q) (Next Q)

Q: Is is possible to operate D-Star from a software-defined radio? Tags: modes (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) What is preventing a software-defined radio from transmitting the D-Star protocol? Tags: modes (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) User: paul-v Answer

by kawfey

Nothing is preventing an SDR from transmitting the D-STAR protocol, other than the need to implement it as such. It is open, and currently I know that Digital Signal Decoder (DSD) can actually decode some data and textual frames. What prohibits transmission of D-STAR Digital Voice is the codec used to encode the voice - it’s AMBE2000 , which is patented and proprietary. A license for one of these is in the ballpark of $100,000, allowing only large businesses to use it. Icom, having already developed P25 hardware using the AMBE codec, is the only one to do so thus far, aside from the DVDongle (though I don’t know how they can afford to use it). The reason why AMBE was chosen was because it was the only low-bitrate RF speech codec available at the time. Now, if codec2

can be implemented over D-STAR (or its own protocol, like FreeDV), it

would be completely open. This is certainly a future development. Answer

by phil-frost

Nothing. In fact, the UDR56k

is an SDR and transmits D-STAR.

If you want D-STAR digital voice, you do need to purchase an add-on card which contains an ASIC from DVSI implementing the propritary AMBE codec , or pay a substantial (but undisclosed publicly) licensing fee. One can safely assume that any licensing agreement would forbid any free proliferation of the implementation. The DVDongle contains the same ASIC, visible here as the large IC on the right, with “AMBE-2000” printed on it:

The middle IC is at Atmel microcontroller, and the IC on the left looks like an FTDI USB interface. There’s not much else to it. Answer

by k7aay

The propretary AMBE codec prevents you from using D-Star for voice. Without that codec, you can’t talk over D-STAR. However, you can use the DV Dongle to talk with D-Star users over the Internet. Tags: modes (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q)

Q: Is FM appropriate for foxhunting? Tags: modes (Prev Q) (Next Q), ht (Prev Q) (Next Q)

I’m thinking about an inexpensive way to create a foxhunt kit for youth groups, and am wondering if the cheap dual band HTs could be used. However, it occurs to me that FM doesn’t provide any good audio queues for signal strength, and the SWR meters on these units are typically useless. Can such FM radios be used for foxhunting, and how? If there’s a better and cheaper method, please consider addressing it in my related question here. Tags: modes (Prev Q) (Next Q), ht (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

Yes they can. You are right that the cheap HTs don’t have much of a useful meter (I own a couple). Two easy solutions are 1) body fade and 2) directional antennas. Body Fade Hold your HT close to your chest and turn around slowly, looking for the direction where your body blocks the most signal (the signal null). Now you know that the signal is coming from behind you. turn around, walk that way, rinse and repeat. The signal should get stronger. Note that the null you are creating is rather shallow. At VHF/UHF frequencies, it can be filled in by signal reflections off of nearby objects. So try to avoid large buildings, chainlink fences, metal signs, etc. If you are not getting a good null, move to a clearer location and try again. When the signal is so strong that you can’t find the null, tune 5 or 10 KHz off frequency to put the signal into the skirts of the receiver’s IF passband. If your hand-held is dual-band (144/440 MHz) and you are hunting on two meters, try tuning to the much weaker third harmonic of the signal in the 70 cm band while performing the “body shield.” Disconnecting the HT’s “rubber duck” antenna will knock down the signal even more. Hearing the signal with antenna off is usually a “You are here!” indicator. Directional Antennas Fox hunting on 2m means there are a variety of simple directional antennas you could build that are also quite inexpensive. A 3 element yagi is a good choice as a small loop. there are several examples of yagis made from steel measuring tape, making them quite durable and easy to pack. See the site

for lots of good information.

Tags: modes (Prev Q) (Next Q), ht (Prev Q) (Next Q)

Q: What does a SSB frequency actually indicate? Tags: modes (Prev Q) (Next Q), frequency (Prev Q) (Next Q) An SSB signal is an AM signal with the carrier and other sideband filtered out, if I understand correctly. As such, when specifying an SSB frequency do you specify the carrier frequency, then state which sideband, or do you specify the frequency the sideband is actually centered on? Tags: modes (Prev Q) (Next Q), frequency (Prev Q) (Next Q) User: adam-davis Answer

by michael-kjörling

Normally in amateur radio when specifying a frequency you specify the nominal carrier frequency. For SSB and other suppressed-carrier transmission modes, you specify the frequency to which the BFO needs to be tuned to re-insert the suppressed carrier. For this to work, you also need to specify which sideband you are transmitting on; lower, upper, or both. (Remember it’s possible to have suppressed carrier double sideband, with identical or separate modulation of the sidebands.) Even if you specified the center frequency rather than the suppressed-carrier frequency, you’d still need to specify which sideband you are modulating. If you get the sideband wrong, the audio will sound very strange because the demodulation will be inversed compared to the modulating signal. You can try this out for yourself by e.g. using USB to scan across the 7 MHz amateur radio band, where by convention the lower sideband is used. For CW and other carrier-only transmission modes, it means that you specify the actual center frequency of your transmission. (It’s a center frequency because the on/off keying causes sidebands to appear around the center frequency.) The receiver’s actual BFO frequency is offset from this value by some amount, normally 400-700 Hz, to generate an audible tone at a reasonable frequency. Most modern transceivers allow you to configure the BFO offset for CW. The above, combined with the fact that SSB often uses a 300-2700 Hz modulation passband, means that on SSB you normally aren’t actually transmitting on the indicated frequency, only near it. Note that other services may do things differently, and that channel-based amateur radio allocations may actually specify the center frequency rather than the BFO frequency. This is done e.g. for the 5 MHz amateur radio channels in the US , which are legally specified as center frequencies with a maximum total transmission bandwidth. Answer

by phil-frost

SSB is, as you say, half of AM, without a carrier. That’s the way to think about it if you are implementing it with traditional analog electronics. However, here’s a simpler way to think about it: SSB is the baseband signal shifted up into RF. Human hearing works from about 20Hz to 20,000Hz. Human voice needs only up to about 4000Hz. So, take your voice from 20Hz to 4000Hz, and shift that up to 14,000,020Hz to 14,004,000Hz, and you have SSB. (Although you are in the CW band, I won’t tell anyone.) Specifically, this is USB. LSB is the same, except all the frequencies are backwards: higher frequency is baseband is lower frequency in RF. The dial frequency in either SSB mode is the one that corresponds to 0Hz in baseband. So, for USB, the dial frequency is the lowest frequency in the transmission passband, and for LSB it’s the highest frequency. Typically the passband is 4kHz wide to accommodate human voice with reasonable fidelity. Tags: modes (Prev Q) (Next Q), frequency (Prev Q) (Next Q)

Q: 1200 baud packet radio can’t communicate Tags: modes (Prev Q) (Next Q), diy (Prev Q) (Next Q), packet (Prev Q) (Next Q) I’m toying with a simple 1200 baud packet radio I built. I’m attempting for it to be compatible with APRS, which uses the Bell 202 signaling, 1200Hz for mark and 2200Hz for space, which I assume map to 0 and 1 respectively. However it’s not communicating with the commercial TNC I’m using or testing. I’ve tried mapping 1 to space and 0 to mark as well, but that doesn’t work either. Tags: modes (Prev Q) (Next Q), diy (Prev Q) (Next Q), packet (Prev Q) (Next Q) User: adam-davis Answer

by rocketmagnet

If you’re used to dealing with protocols between chips, like UART, SPI and I2C, then APRS will feel quite strange. Whereas if you’ve been involved with CAN, Ethernet, USB at the low level, then APRS will seem quite familiar. It’s not as simple as 1200Hz means 0, and 2200Hz means 1. There are two things which make it different, firstly bit-stuffing, and secondly NRZI encoding. Bit-Stuffing For reasons that will become clear in a moment, you’re not allowed to transmit more than 5 1s in a row. If you want to transmit more than five 1s in a row, you’ll have to stuff extra 0s to break up the string of 1s.

NRZI Non-Return to Zero inverted is an alternative way to encode a bit stream. Surprisingly, it’s the change from one frequency to the next which encodes 0 and 1. Between each 1/1200th of a second, if the frequency changes, that’s a 0, and if it doesn’t change, that’s a 1. Take your original bit stream. Imagine turning all the 0s into edges, and all the 1s into notedges, like this:

Then join up the edges, like this:

The receiver uses the frequency changes to synchronise itself to the incoming bit stream. It needs to do this fairly often to make sure it stays synchronised. This is the reason that a long string of 1s isn’t allowed. A long string of 1s means a long time without any frequency changes. For more information on implementing APRS, there’s a good set of blog posts on Hugo’s Projects which goes into detail about all of the implementation issues. Answer

by adam-davis

While 1200 baud packet radio uses AFSK with 1200 and 2200 tones, they don’t correspond with digital 1’s and 0’s directly. It employs NRZI encoding as well as bit stuffing. Non-return to zero inverted (NRZI) means that a 0 is encoded as a change in tone, and a 1 is encoded as no change in tone. This depends on having an accurate clock on both ends. But even with a decent clock, a long string of unbroken 1’s will end up providing no changes in tone, and after awhile the clocks will drift apart, and the receiver may think it’s on the 50th 1 in a row, while the transmitter is on the 49th 1 in a row, because the tone is never changing. For that reason if there are five 1’s in a row, a 0 is inserted at the end of the fifth 1. This forces a tone change, so that the receiver can match its clock with the sender at least every 5 time periods based on the tone change. The receiver, upon seeing a tone change after 5 time periods of no tone change, discards the tone change (the digital 0), realigns the clock, and continues to decode the bitstream. There is one time you might see 6 1’s in a row, but that is a special flag on the AX.25 protocol, so it’s not technically part of the 1200 baud system. It’s common in packet radio, though, so it should be kept in mind. I found this, and more, at “1200 Baud Packet Radio Details

” by N1VG.

Tags: modes (Prev Q) (Next Q), diy (Prev Q) (Next Q), packet (Prev Q) (Next Q)

Q: How does SDR demodulation differ between wideband and narrowband FM?

Tags: modes (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) What is the difference between software demodulation of an IQ signal between wideband FM and narrowband FM? Both seem to look at the 2nd difference in unwrapped phase angles of IQ samples. Tags: modes (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) User: hotpaw2 Answer

by kevin-reid-ag6yo

There are actually three different distinctions one could mean by referring to “narrowband” FM. Wideband FM in this context generally refers to the type of FM used for broadcast stations — those picked up by consumer FM receivers — as opposed to that used by two-way communications, including amateur transceivers. You are right that there is no fundamental difference between them in how the frequency modulation is demodulated via DSP. In both, the difference between the instantaneous frequency of the signal from some nominal carrier frequency is proportional to the modulating (audio) signal. The distinction is in the maximum deviation, which is closely related to the occupied bandwidth. That is, if you modulated either type of FM transmitter with a signal at, say, 50% of maximum input level, the wideband FM signal would have a much larger deviation for the same signal. The advantage of this is that wideband FM has higher fidelity and picks up less noise, because the larger instantaneous frequency changes are less easily affected by noise. You could in principle demodulate either type of FM with the exact same demodulator with the same settings; however, the wideband FM would come out louder because of the larger deviation. In practice, you also need a filter before the demodulator which removes all the noise or other signals which would interferes with the instantaneous-frequency demodulation; this is what actually makes the biggest difference. To a narrowband receiver, a wideband signal is extremely over-deviating; the frequency repeatedly moves entirely out of the filter passband, so that all but the zero-crossings of the signal are replaced by noise. To a wideband receiver, a narrowband signal is extremely quiet. An additional difference in practice, not inherently related to the deviation and bandwidth, is that wideband FM signals may include stereo or other additional information. Stereo is actually added to the modulating signal — that is, the FM modulation is unchanged. The “pilot tone” and stereo difference signal are added to the mono audio but shifted to a frequency high enough that they do not conflict with the audio frequencies and a typical mono receiver will not reproduce them. Wikipedia has a nice plot of what you might find in a broadcast FM signal — this is an “audio” spectrum, so you will not see these things laid out on a waterfall display. Another “wide vs. narrow” distinction you might hear about: there are two different

maximum deviations (5 kHz and 2.5 kHz) that have been used for two-way radios — in the US, the FCC required a shift to the narrower bandwidth to enable using more channels in the same spectrum; this event was called “narrowbanding”. Amateur equipment is under no such requirement and to my knowledge still typically uses the wider (5 kHz) deviation. In radio software I have seen these distinct modes being cryptically labeled “NFM1” vs. “NFM2”, or “FM” vs. “NFM”, whereas broadcast FM is usually “WFM”. Finally, in the theory of modulation , FM is called wideband if the maximum deviation significantly exceeds the highest modulating frequency, and narrowband if the highest modulating frequency significantly exceeds the maximum deviation. By “modulating frequency” we mean the frequencies present in the modulating signal (the audio signal). This relationship affects the effective occupied bandwidth of the signal, and therefore the choice of low-pass filter used to select the channel before demodulating it. Tags: modes (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q)

Q: What should be the modulation when transmitting APRS signal? Tags: modes (Prev Q) (Next Q) Is it SSB or NFM or other type of modulation? Tags: modes (Prev Q) (Next Q) User: harold-chan Answer

by wprecht–ab3ry

APRS is a data transmission protocol and is independent of the underlying connection details. So there is no required modulation for the protocol. That said, the common implementation of APRS is FM modulated 1200 baud AFSK in the 2m band. Several major vendors like Yaesu and Kenwood support the protocol with built in functionality for APRS. There have also been implementations of the APRS protocol over AX.25 on HF frequencies as well.

and PSK31

Tags: modes (Prev Q) (Next Q)

Q: Is frequency hopping a viable solution for privacy and security without encryption? Tags: modes (Prev Q) In terms of radio transmission, three major issues seem to arise for various sensitive transmissions:

1. Others do not gain access to the content of the message 2. Others cannot determine the location of the sender 3. Others cannot block message channels 4. Others do not know a message is being sent at all In terms of amateur radio and non amatuer radio in different bands (if this is applicable) and different protocols/specifications (if this is applicable), how well does frequency hopping (without encryption) address each of these issues both in terms of avoiding the accidental observer, deliberate amateur (not as in amateur radio but amateur as in nonprofessional) observer, and determined professional government/authority observer. BONUS: How well does frequency hopping work in these matters when combined with encryption? Tags: modes (Prev Q) User: j-s Answer

by kevin-reid-ag6yo

1. Others do not gain access to the content of the message In the US amateur radio service, transmitting “messages encoded for the purpose of obscuring their meaning” is prohibited by §97.113 and specifically for spread-spectrum (SS) by §97.311 . I would imagine other jurisdictions have similar rules which prohibit such transmissions and/or require that hopping patterns etc. be published. I’ll leave the detailed question of whether it is useful for this purpose when legal to others who are more familiar with the technical aspects of spread-spectrum modulation. Some remarks from general principle follow. 2. Others cannot determine the location of the sender No method can give you this as an absolute guarantee. Someone can always take a wideband receiver and a directional antenna and look for where the received power is higher. All that spread-spectrum gets you here is requiring the receiver to have a wider bandwidth, therefore being unable to filter out unrelated signals from other radiators, making it harder to find the transmitter at a longer distance. 3. Others cannot block message channels Spread-spectrum techniques increase the power requirements of jamming, because the jammer must decrease the SNR sufficiently across the entire bandwidth and not just a narrow band. 4. Others do not know a message is being sent at all This falls into the same category as point 2; as you move away from the transmitter, a spread-spectrum transmission will apparently disappear into the noise floor sooner, but if

you are close enough a transmission is obvious no matter what the frequency. For the “accidental observer” as you put it, not attempting to decode spread-spectrum transmissions, they will receive the SS transmission as a (possibly imperceptible) increase in the noise floor. Thus, spread-spectrum signals are indeed unlikely to be accidentally received (or interfered with). Answer

by bradley-evans

Frequency hopping is more typically considered an ECCM measure. That is to say that a transciever that continuously cycles frequencies in accordance with some “hop set” is more difficult to jam than a single-channel radio system. In and of itself, it doesn’t constitute proper encryption of your signal — you are still transmitting data in plain text. It would make it more difficult for unmatched hardware to receive your signal in its entirety, but considering the narrow bands of spectrum you’re allowed to operate on with an amateur license I’d be extremely concerned about inadvertently causing interference as your radio hops across the spectrum. I’ve only really seen freqhop implemented on the VHF spectrum as an ECCM measure, and other matched radios designed to talk on that net need carefully matched radio time (a time drift of as little as a second would cause a radio to fall out of net). It would not obscure that you’re sending a signal at all — on the contrary, a frequency hopping radio would, to me, be quite notable and draw my attention. If your objective is to prevent your signal from being received by third party stations, the tried and true solution is to use a directional antenna. This also wouldn’t run afoul of any FCC regulations and would actually help mitigate interference, in my opinion. Tags: modes (Prev Q)

Procedure Questions Q: How do I report an emergency using ham radio? Tags: procedure (Prev Q) (Next Q), emergency (Prev Q) (Next Q), frequency (Prev Q) (Next Q) If I’m in the wilderness with ham equipment but no phone signal, how would I report an emergency? Is there a particular frequency I would use, a particular protocol or suchlike? Tags: procedure (Prev Q) (Next Q), emergency (Prev Q) (Next Q), frequency (Prev Q) (Next Q) User: berry120 Answer

by walter-underwood-k6wru

On voice, use “Mayday Mayday Mayday” at the beginning and end of the transmission. This is only for life-threatening emergencies. For other emergency situations, like reporting a wildfire that does not directly threaten you, use “Break Emergency” at the beginning of the call. This is a good guide to making emergency calls: The IARU has established global emergency frequencies. They call these “Emergency Centre of Activity Frequencies”. 15m 21.360 MHz 17m 18.160 MHz 20m 14.300 MHz

In the US, 14.300 MHz has an organized group of monitors (


A full list of regional and country-specific emergency frequencies is here: option=com_content&view=article&id=891&Itemid=246 The Wilderness Protocol for VHF/UHF ( ) is useful if you have line of sight communication. That might not be the case in mountainous terrain. The Wilderness Protocol was started in the US, so I have no idea how often it is used outside the US. Finally, amateur radio requires practice for effective emergency use. In a group, you need at least two practiced operators, because one of them might be injured. In most situations,

a satellite phone is a better and more reliable choice for backcountry emergency communication. I go into more detail on that in this blog post: One good way to get practice with back country operating is to participate in Summits on the Air (SOTA). The common SOTA frequencies might also be a good choice for secondary emergency frequencies, because the SOTA “chasers” often monitor those. Answer

by michael-kjörling

Assuming that you have an amateur radio license makes this easier, but it’s quite possible that the UK legal language includes provisions that may be applicable and allow transmission without a license. It depends on the specifics of the emergency in question. I would strongly recommend familiarizing yourself with the relevant definitions in the legal code of your country; it’s perfectly possible that an emergency situation allows you to transmit on frequencies you otherwise wouldn’t be allowed to, even if the emergency situation does not revolve around you directly (for example, you tune your transceiver across the bands without a license and come across an emergency transmission by someone else). If possible, find a frequency that is actually in use and where you can hear both stations; it makes it much more likely that someone will hear your call. Call mayday mayday mayday (life-threatening emergency) or break break emergency (non-life-threatening emergency) as soon as is practical (on a handover if you can afford to wait that amount of time), and unless the situation is extremely dire wait a few moments for acknowledgement. Hopefully one of the stations will respond with something like Jim, break for emergency, go ahead emergency. As the remote operator making such a go-ahead request, you want to be extremely concise, clear, and unambigiously tell the breaking station to go ahead with its transmission and all others to cease transmission. Ideally, at this point the remote station operators will have grabbed a blank piece of paper and a writing utensil of some kind, and be prepared to take notes. For the receiving stations to be taking notes is absolutely essential; as a receiver you will not remember the details! Also, all stations able to receive an emergency report should copy it down; if the station making the emergency report goes off the air for whatever reason, the chances are much better that even in the case of heavy interference a complete report can be pieced together by the remaining stations. Then, I would suggest reporting things in logical order. Stay calm. Consider what information is needed to offer assistance. For a wilderness emergency, I’d state: The kind of emergency (broken leg, vehicle collision, wildfire, …). The position, in some unambigious manner (for example “Grothwick national park distance 30 miles east of Tadwick, distance 12 miles direction north from trail head on the length 72 miles trail”). Spell out numbers (“seven two”, possibly even “seven two point zero” rather than “seventytwo”). GPS coordinates if available will greatly help, but if it’s an actual emergency, I wouldn’t wait for the GPS receiver to get a fix; you can always complement later. The assistance required (“need transportation to nearest hospital”, “need fire

prevention services”, …) After that, STOP. Say “any receiving station, confirm complete reception of emergency report” or something equally unambigious. Hopefully someone will acknowledge, or at least ask for a repeat of some missed piece of information. Note that there may be stations listening without transmission capability so a lack of response does not necessarily mean that nobody heard you. The ability for a remote station to acknowledge is why I suggest finding a frequency that is actually in use and breaking into the communications. With any luck, a remote station will respond with something like “confirming complete reception of emergency report, stand by”. This is the kind of answer you want. It means they have received everything and is contacting the proper emergency services through some alternate channel, whether that is radio relay, telephone, or some other means. Respond with a short “emergency, standing by” to acknowledge. Issue repeat “emergency, standing by” every 20-30 seconds or so to make it less likely that anybody thinks the frequency is free for use. Hopefully, a minute or two after the initial acknowledgement, the acknowledging station will get back to report that emergency services have been notified about the emergency. At this point, they may relay questions, instructions or otherwise from the emergency services dispatch center. Answer those to the best of your ability, as clearly as you can, just as if you had been calling them yourself. You may notice an overall theme in all this: clarity, and the repeat transmission of “emergency”. Both those serve to help everyone involved. A panicked report does not help anybody, as well as that a random radio amateur is less likely to be trained to deal with someone panic-struck than an emergency services dispatch operator. Repeatedly transmitting “emergency” informs others that the traffic should have extremely high priority. Clarity, including avoiding the use of jargon, helps non-amateurs copy and possibly relay the message to the emergency authorities. All this helps ensure as speedy a response as possible. The exact wordings are much less important than doing your best to remain calm and to provide the pertient information as soon as possible. In a real emergency situation, I wouldn’t worry too much about identification. Do it early if you have the time, but if not, it’s better to wait until all essentials have been taken care of. And certainly don’t bother with signal strength reports etc. unless the signal quality is exceptionally poor to the point of being outright hard to copy accurately. This is an emergency report, not a rag-chewing amateur radio contact! Answer

by jeepescape

If this is something you are interested in on an ongoing basis as a volunteer, then you should look into joining RACES and/or ARES in the US, and RAYNET in the UK: In fact, during major emergencies and disasters, one or both of these organizations may be

the only hams allowed to operate, and it will be a very organized effort. Outside of that, here are the US regulations for licensed hams: § 97.403 Safety of life and protection of property. No provision of these rules prevents the use by an amateur station of any means of radio communication at its disposal to provide essential communication needs in connection with the immediate safety of human life and immediate protection of property when normal communication systems are not available. § 97.405 Station in distress. (a) No provision of these rules prevents the use by an amateur station in distress of any means at its disposal to attract attention, make known its condition and location, and obtain assistance. (b) No provision of these rules prevents the use by a station, in the exceptional circumstances described in paragraph (a) of this section, of any means of radio communications at its disposal to assist a station in distress. This basically says that under those circumstances in the US, you can operate in any band, in any mode, in an effort to communicate the distress, including the ones you are not licensed for. Tags: procedure (Prev Q) (Next Q), emergency (Prev Q) (Next Q), frequency (Prev Q) (Next Q)

Q: Ok to use any repeater? Tags: procedure (Prev Q) (Next Q), repeater (Prev Q) (Next Q) There’s a number of repeaters in my area, each belonging to a particular amateur radio club. These guys are all friendly and willing to chat but I was wondering if it was bad form to make use of a repeater belonging to a club you aren’t part of without first getting permission? The repeaters in my are are all listed on the websites for each club but no operating conditions are mentioned, I’ll ask but was thinking there might be a general rule. Tags: procedure (Prev Q) (Next Q), repeater (Prev Q) (Next Q) User: s3c Answer

by dan

Do you have to get permission? No. Few have issues with guests on a repeater (think of travelers passing through, for instance). In the U.S. they can legally prevent someone from using their repeater (see ECFR Title 47, §97.205(e) ), but this is not the case in many other countries (repeaters are generally open for all to use). Should I frequently use a repeater that I don’t financially support? This is an ethical question, so subjectivity abounds. However, it should be kept in mind that repeaters aren’t free nor cheap to set up and maintain. Consider paying membership dues or making a donation to the club(s) that maintain a repeater that you use frequently. This will help offset the operating costs and you’ll gain some new friends.

What operating conditions should I follow? There is of course general repeater etiquette (listen first, wait for the courtesy tone, don’t kerchunk, use plain language, don’t call CQ, etc.), but some clubs may have specific etiquette or pet peeves that you will only find out about in their newsletter (or by attending their meetings). It is generally a good idea to remain somewhat connected to the club that is the control operator of the repeater if you use it frequently. You may also be able to help the other repeater users by learning about a local jammer or other problem as well. Answer

by oh7lzb

The practices vary greatly between areas and countries. In many countries “closed repeaters” don’t exist, or are forbidden. In some countries private repeater systems are common, but public ones still exist. Those private repeaters are still likely to happily accept visitors (travellers, for example). It’s probably best to ask the guys on the repeater - they should be happy to tell you what’s the local practice. Many repeaters have web sites too, which provide usage instructions and other policies. If it’s not described as a closed or private repeater, it’s safe to assume that it is open and free for all. If you become a regular visitor on the repeater, it’s a good idea to join the club to share the operating costs. Answer

by ke3fl

In my experience since 1992 with some traveling in MD, VA, PA, DE, WVA, NC, FL, CA, & OK I have yet to find a repeater group that has not been friendly to a newbie or visitor. I do usually have the ARRL repeater book with me and am careful to stay off of the few closed repeaters listed. Tags: procedure (Prev Q) (Next Q), repeater (Prev Q) (Next Q)

Q: If I hear a distress call, what is the correct procedure for helping the person? Tags: procedure (Prev Q) (Next Q), emergency (Prev Q) (Next Q) If during normal operation, I receive a mayday or pan-pan call, how should I handle this? Am I required to provide help in this situation, and what can I do to make sure I give all the assistance needed, what information should I try and get? If someone else is working with the station on the distress call, should I join in and help? Tags: procedure (Prev Q) (Next Q), emergency (Prev Q) (Next Q) User: david-vk2vxk Answer

by michael-kjörling

First, if you hear a distress call: STOP! Immediately end any transmission in progress. Do not touch any antenna or radio controls except as needed to turn off split operation etc.

Lock the VFO to avoid inadvertantly bumping the frequency setting. Particularly, do not reorient the antenna in an attempt to get a better signal. Focus on copying what you can and avoiding any activities that may cause interference. This is something you can actually practice: how long does it take you to reset RIT, turn off split, lock the VFO and getting ready to actually write things down? Then, I view it as a multiple steps process. Copy the message. You will not remember the details. Write down everything, clearly marking anything you are not absolutely certain about. This is a major reason why I feel one should always have writing utensils within easy reach from one’s operating location; the odds that you’d receive a distress call are small, but if you do, any old pencil and back of a log book page will help tremendously. Wait to see if a station better equipped to handle the distress call responds. Maybe there’s someone closer, or with necessary knowledge (for example, there’s the possibility that a doctor hears a distress call that is about a medical emergency). If nobody answers within a few seconds (and you are sure that nobody does and you aren’t simply out of range of the other station), briefly identify yourself and then stop transmitting again. This might be something as simple as “amateur radio station VK2VXK received distress call - distressed station please confirm, over over”. Your transmission lets anyone within range of you but out of range of the distressed station know that the frequency is in use for emergency traffic (a definite signal to cease transmissions), and if you get a confirmation from the remote station you have established two-way communications. I’d use the remote station’s call sign if they gave one, but don’t worry if they didn’t. In many jurisdictions, emergency communications is allowed on any frequency unlicensed if needed to solicit help. In many jurisdictions this also means that you can respond to a distress call even if you are normally not authorized to transmit on the frequency in question, if doing so is necessary to provide emergency assistance. As soon as you have “claimed” the distress signal by receiving confirmation from the remote station, tell the remote station to stand by and pick up the phone and call emergency services. Immediately inform them that you have received a distress call over radio (so that they do not rely on locating your phone line to determine the location of the emergency), and accurately relay all information in the distress call. Particularly important are the type of emergency, how many people are involved, and the distressed party’s location. Be prepared to relay questions and answers between the emergency operator and the distressed station. Stay calm (easier said than done, but very important). Maintain communications with both parties until you receive confirmation that emergency services have arrived. If you hear anyone transmitting on the frequency, immediately calmly inform them that the frequency is in use for emergency distress traffic. If someone else has already established communications with the distressed station, then do not interfere. Also, do not play radio cop. If some other station starts transmitting on the frequency, let either of those already communicating deal with it. Instead, simply copy all details you can, stay on the frequency and do your best to be prepared to jump in if

either of the stations ask for assistance which you are able to provide or the station that is in communication with the distressed station clearly goes off the air, but not under any other circumstances. I doubt you would be legally required to provide assistance to a distressed station, but if it was me, I would sleep considerably better at night knowing I did whatever I could to help, even if it was something as simple as ceding a frequency to a station in distress. Actual emergency or distress communications always has precedence over all other communications. Answer

by tylerl

As an addendum to the answer provided by Michael, there’s also the point of what information to obtain from the distressed party. If they’re a “professional” or have otherwise had some sort of relevant training, they’ll probably rattle off a whole checklist of bits for you to record and relay. Listen carefully, write fast, and read back to confirm all of their data points once they’ve finished talking. If instead they’re just someone with a radio, then you’ll probably have to ask questions to direct their attention to the important details. Ideally you’ll want to get the specific questions to ask from the emergency services you call. But depending on the circumstances, maintaining a three-way conversation may not be possible. So here are some important details you’ll want to gather in pretty much every instance. Much of this is taken from aviation emergency handling, but applies in the general case as well: 1. What is the nature of the emergency - Plane crash? Hiking accident? Lost? Typically you won’t have to ask, this is almost certainly going to be the first thing they tell you. 2. Who are you - Again, another obvious one, but getting an identity can help focus rescue efforts. 3. Where are you - You may have to ask for further clarification as they may assume you already know more than you do. Which state? Nearest city? Closest road? Landmarks? “What do you see?” If a search party is going to have to be sent, then the more detail you can get the better. 4. How many people are there - this is the “number of souls on board” question from maritime and aviation emergency handling. Most people won’t even think to offer this detail, but it’s one that every emergency responder will want to know. A headcount is invaluable, but if you can get it, a list of names is even better. 5. What are your intentions - Though most emergency advice boils to “stay where you are”, you probably won’t be in a position to make recommendations. But you can get an idea of what they are thinking. Find out their plan, their backup plan, and what they intend to do if that doesn’t work out. While the individual may say “I intend to stay right here,” it can be helpful to ask, “if you do leave, which direction do you think you’ll you go?” Lots of rescue effort is spent on guessing people’s backup plan. 6. What do you need - While you’re not in a position to offer aid, it is helpful to get a

list of their needs, so that rescuers can prepare accordingly. (“Alice has a broken leg and Tommie needs insulin”) You’ll need to use your judgement to determine what to ask, or indeed whether you should ask any questions at all. As a rule, keep your communication clear but very brief. It’s not uncommon for someone to have only a few moments to get a transmission out while being otherwise busy managing their emergency. Tags: procedure (Prev Q) (Next Q), emergency (Prev Q) (Next Q)

Q: What is the process of making a voice contact? Tags: procedure (Prev Q) (Next Q), contest (Prev Q) (Next Q), phone (Prev Q) (Next Q) I got into Amateur Radio for emergency preparation and to allow me to expand my electronics hobby. Initially I didn’t find much value in contesting or making contacts, but apparently there are some valuable skills one can gain from contesting. I spent some time listening to voice contacts, and the process appears to be fairly consistent, but I’m worried I might do something wrong, so before I jump in, what is the process of making a contact? Is there a simple flowchart one might follow if exceptions happen during this process? Tags: procedure (Prev Q) (Next Q), contest (Prev Q) (Next Q), phone (Prev Q) (Next Q) User: adam-davis Answer

by michael-kjörling

First off, amateur radio isn’t very strict. With few exceptions, nobody is going to be very upset if you miss out on something during a casual contact. If you mess up too badly, you’ll be asked to provide the missing piece of information, be it a signal report, location, repeat your call sign because it couldn’t be copied, or whatever the issue may be. So don’t be too worried about trying and failing. I’ve had people copy my call sign wrong on occasion too and it isn’t a big deal; just grounds for a repeat of it, is about all. For a non-contest (“rag-chewing”) contact, it’s largely free-form. The first step is to announce your presence, or find someone looking to make contact themselves. On HF the standard way to do this is to call CQ (“seek you”); on repeaters practice varies, but it shouldn’t be too bad calling CQ there either. You can also tail-end someone else’s QSO, calling them up as they finish their contact. Don’t make too long a CQ; you want to attract attention, not bore people to death before giving them a chance to respond. Even on HF SSB, a three-by-two CQ (three CQ followed by your call sign twice), possibly repeated twice, is usually plenty enough. If it doesn’t attract attention you can always try again, or recognize that the frequency may be in use by a station you cannot hear. Or that simply nobody wants to talk to you, though that’s quite rare. A CQ might be “CQ, CQ, CQ, KD8OAS Kilo Delta Eight Oscar Alpha Sierra. CQ, CQ, CQ, KD8OAS Kilo Delta Eight Oscar Alpha Sierra, calling CQ and by”. Here, “calling CQ

and by” is a fairly common shorthand for “calling CQ and standing by for a call”. Don’t rush things; someone hearing you may need to tune their antenna before they can answer, for example. Give it at least a minute or two before giving up on the frequency. Something that does irk me is when people get the order of the call signs wrong. It’s “to from from“, not the other way around. So if you were to call CL1SGN on amateur radio, it’d be “CL1SGN from KD8OAS”, not “KD8OAS to CL1SGN”. Some people will actually go so far as to ignore a call if the call signs are given in the wrong order; and with a garbled transmission, you risk mistaking one station for the other. Assuming the remote station answers your call, unless they know you from before it will usually be a pretty brief transmission just to tell you they heard you and are willing to make a contact. Technically, at this point you have established contact. At that point, you’ll usually give the call sign pair again, followed by your first name and location (to whatever precision is called for). Many also give a basic equipment report stating transceiver model and antenna type and (for non-repeater contacts) mention the amount of power they are putting out. If you are able to judge it at this point, also give a RST (signal) report, then hand over to the other station with something like “CL1SGN from KD8OAS, go ahead”, at which point the other station will generally respond with the same information. By the time they are finished, you should definitely be able to give an appropriate signal report. Beyond that, the QSO may take off in almost any direction. Just keep in mind the legal limits on what can be discussed over amateur radio, as well as topics that are best not discussed (politics being one of them). By the time you feel happy with the contact, just courteously conclude it. This doesn’t need to be very fancy at all. “Well Jim, it’s been nice talking to you. I’ll be sending a QSL card via the bureau if that’s fine with you. I’m OK in the call book or via the bureau. Have a good evening and maybe we’ll talk again some other time. Seven-three and back to you.” There are two ways of sending QSL cards, “via bureau” (through the amateur radio association in your country) or “direct” (mailing it directly to the other station). If you want a QSL card “direct”, be sure to say so as well as state whether (it better be!) your address is correct in the amateur radio call book. Also, don’t expect unsolicited QSLs for contest contacts, and don’t give such extraneous details during a contest contact; just send a QSL yourself and write “PSE QSL” (“please QSL”) on it. The remote station will likely tell you either that they don’t accept QSLs via the bureau or that they are OK in the call book as well. Either way, note it in your log if you want to send a QSL card later. At this point, it’s pretty much up to what you want to do next. As a general rule, it is commonly said that the station that called CQ “owns” the frequency (because they were “there” first), and it’s courteous to either disown the frequency (“you can have the frequency, Jim”) and/or state that you are going off the air (“KD8OAS going QR-tango”, for QRT meaning you are closing down your station). Remember to finish with stating both call signs involved, so that anyone listening in will know who made contact with whom. Once that’s all over, write down the conclusion time for the contact in your log book, grab a blank QSL card from the pile, fill it out, put a stamp on it and place it in your “out” pile. Then, go reward yourself with a cup of hot cocoa or whatever strikes your fancy.

The contents of a contest contact will depend very much on the specific contest, but is generally pared down to the absolute minimum: call sign, signal report (normally a simple “five nine” even if the signal really isn’t, to save time) and whatever the contest exchange happens to be; a locator, serial number, or something else. The basic form is the same, only sped up about 10× or so. During a contest, if you are holding a frequency you might not even give your own call sign more often than every half dozen contacts or so. Of course, if you are scanning across the band and working whatever stations you can find, you’ll need to give your call sign each time as nobody on the particular frequency will have any idea who you are otherwise. A contest CQ is also much shorter, sometimes shortened as much as to just your own call sign once followed by the word “contest”. Tags: procedure (Prev Q) (Next Q), contest (Prev Q) (Next Q), phone (Prev Q) (Next Q)

Q: My neighbor is complaining about my transmissions, what can I do? Tags: procedure (Prev Q) (Next Q), rfi (Prev Q) (Next Q) My neighbor has indicated that they can hear noise from their computer amplified speakers when I’m transmitting. We’ve done a few tests and it does appear that it’s my transmitter that’s causing the noise. I’ve performed some testing and determined that I’m well within my operating limits. The transmissions are clean, within power limits, etc. There is nothing I can do on my end to resolve the problem, other than cease transmission. My neighbor is unwilling to replace his speakers with a more noise resistant set, though he may be willing to allow minor modifications if it doesn’t otherwise affect performance. What should I try that should help remove, or at least reduce, the noise on the speakers? Tags: procedure (Prev Q) (Next Q), rfi (Prev Q) (Next Q) User: adam-davis Answer Wikipedia

by vu2nhw writes to say

By the regulation, the FCC DoC certification mark is mandatory for devices classified under part 15 (IT equipment like computers, switched-mode power supplies, monitors etc., television receivers, cable system devices, low-power transmitters, un-licensed personal communication devices) and part 18 (industrial, scientific, and medical (ISM) devices that emit RF radiation) of the FCC regulations. The subject is covered in some depth on form edit applied by me)

which writes to say (free-

Rectification and overload are both problems with the design of the affected equipment, and after decades of investigation, the FCC knows this.

In your case, the issue & onus lies upon the manufacturer of the equipment experiencing interference. Having made that clear to the neighbour, you might try introducing a low-pass filter (also mentioned in the article on hamuniverse referenced above) Another alternative (+: dump a load of ferrite beads over their speaker cables. More detailed reading is listed at this site Tags: procedure (Prev Q) (Next Q), rfi (Prev Q) (Next Q)

Q: What is the definition of DX? Tags: procedure (Prev Q) (Next Q) I always believed that DX meant out of one’s own country, and in the continental US that can be pretty far. However, tooling around on the bands I’ll often hear people calling DX inside the US receive responses from others also inside the US. Sometimes the caller will respond, and sometimes not. What is the definition of DX? Is it impolite to answer a CQ DX inside your own country? What should you do if you’re calling CQ DX and someone responds to you who you don’t believe is DX? Tags: procedure (Prev Q) (Next Q) User: adam-davis Answer

by phil-frost

As Wikipedia puts it


The name of the hobby comes from DX, telegraphic shorthand for “distance” or “distant”. There is no objective definition. If it’s far enough that it might be a difficult contact, then it can be DX. Of course this all varies based on conditions, equipment, and perception. Sometimes, callers will specify just what kind of DX they are seeking. “CQ DX Europe.” “CQ DX California”. Etc. Frequently, they are seeking a specific contact to qualify for some award, like worked all states , and they may specify this in the call. If you hear “CQ DX Europe”, and you aren’t in Europe, then probably you shouldn’t return the call. If the call didn’t specify exactly what flavor of DX, then use your judgement. Working Maine to California can be DX, especially with a QRP station. If you think the contact might be challenging or rare due to distance and conditions, then it’s fair game. Also consider what other stations might be trying to return the call. If you hear someone in the same country trying to work someone across the world, then you are not “DX” to the guy in the same country. It would probably be nice if you stayed quiet so he can complete the more difficult contact. During contests, keep in mind what the contest is about. People may explicitly mention the contest in their calls. Reply if you think your contact might be relevant to the contest. If you receive a response to a DX call but you don’t think it is good enough, reply anyway. Maybe the other guy has a question. Maybe he wants to tell you that your transmission is poorly modulated. Maybe he thought you were a challenging contact. Maybe he’s

transmitting with 1mW, and then you will think it was a good contact too, but you won’t know this until you talk. The standard rules of social interaction still apply: be polite. If someone is calling you, they want to talk to you. Tags: procedure (Prev Q) (Next Q)

Q: Is “just listening” on EchoLink considered bad etiquette? Tags: procedure (Prev Q) (Next Q), echolink (Next Q) I was reading about EchoLink and came across this rule under “Access Policies


2. No “SWL” (listen-only) access is permitted. EchoLink is a two-way system by design, and there is no mechanism to validate listen-only stations. I’m pretty sure that by “SWL” they mean unlicensed/public access, but I’m not entirely sure, as I’ve read in several forum threads that it isn’t appreciated when you connect to an repeater/node and don’t identify or say something. I suppose this is because the EchoLink system announces when a remote user connects through the system, but doesn’t necessarily announce the call of the connected station. So is there any reason why I shouldn’t use EchoLink to “just listen”? Or is this just a misconception/misunderstanding on my part? Tags: procedure (Prev Q) (Next Q), echolink (Next Q) User: seth Answer

by peter-kb1avl

The full access policy states (my emphasis): No “SWL” (listen-only) access is permitted. EchoLink is a two-way system by design, and there is no mechanism to validate listen-only stations. The last part is key. You can’t use the echo link system without being a validated licensed amateur. You logistically can not listen to this system without also being allowed to talk on it. Contrast that with “traditional” short wave listeners. Anyone can buy a radio and listen without being licensed to talk on it and there is no way technologically that you can prevent them from listening. My interpretation of the policy is “We don’t support a way for a non licensed station to listen only.” I don’t think that they mean that you aren’t allowed to connect and not talk. I hear stations connect to nodes regularly without saying anything. Perhaps the policy would be clearer if it were written this way:

No “SWL” (listen-only) capability is supported. EchoLink is a two-way system by design, and there is no mechanism to validate listen-only stations. Tags: procedure (Prev Q) (Next Q), echolink (Next Q)

Q: Is there a “proper” phonetic alphabet to use with voice communications? Tags: procedure (Prev Q) (Next Q) When I took my Technician test some 20 years or so ago, we had to memorize the phonetic alphabet, which I think is the same one used in the military. I was taught that it was international, similar to morse code. It used words such as “Mike” for the letter “M” and “Juliet” for the letter “J” and “Zulu” for the letter “Z”. On VHF, I hear these used almost exclusively, but I recently passed my General class exam and started getting on HF and listening to both local and DX stations use words like “Mary” for “M” and “Japan” for “J” and “Zed” for “Z”. Is there really a standard or do people just make up their own? It has caused me quite a bit of confusion since I hear stations use words like “Japan” and I am not sure if they are using phonetics or whether they are actually in Japan. Tags: procedure (Prev Q) (Next Q) User: ghendricks Answer

by hotpaw2

The FAA and ICAO document a standard phonetic alphabet to be used for all aviation radio communication. See: Answer

by pedja-yt9tp

Check Ethic and Operating Procedures for the Radio Amateur ( ). Page 65 shows international spelling and phonetic alphabet. That one you should use when making contacts World wide. However, no one will object if you use some other spelling standard as long as it is doing it’s job - making other side better understand. For example, it is not good to use “Canada” instead of “Charlie”, as “Canada” sounds like having “K” as the first letter. For people who do not speak English natively that is confusing. Sometimes, when other operator has hard time to get your spelling it is good to use different spelling, as different sounding might better get through noise. I noticed that sometimes people have problems recognizing “Tango” in my call as it sounds soft, so if I have to repeat I try using “Tokio” which sounds more harsh and seems to help. Also, if you know spelling in mother language of operator you are in QSO with, that could

really help, not just in making better understanding, but people generally like to find out that others are speaking their language. That is a good way to make people remember you and to start friendship. Tags: procedure (Prev Q) (Next Q)

Q: What is a CQ contest and what is the proper way to respond to a CQ contest call? Tags: procedure (Prev Q) (Next Q), contest (Prev Q) (Next Q) As I listen, I often hear stations calling “CQ contest”. When I hear stations respond, they seem to do so with a specific set of information. I recognize the call sign and a signal report but there are often other pieces of information that seem to be standard that I don’t recognize. When I hear a CQ contest call I am not sure how to respond. Tags: procedure (Prev Q) (Next Q), contest (Prev Q) (Next Q) User: ghendricks Answer

by michael-kjörling

A “CQ Contest” is simply a limited CQ, just like someone can call CQ some-specific-area or CQ any-member-of-a-particular-club. I don’t think I’ve heard this variant on SSB, but I imagine in some contests it may be beneficial to actually specify the contest in question. During a contest, there is usually a specific set of information to exchange. The exact information to be exchanged varies with the contest. This can be for example a serial number, signal report, Maidenhead locator, state/province/county/etc. (usually according to some sort of list of codes), or almost anything else, or a combination of several of these. In order to participate, you must know what the specific exchange is for the contest that the other station is calling CQ for. If you don’t know what the exchange is and what yours should be, don’t respond to a CQ Contest call. The only exception I can think of is if the remote station is calling repeatedly but not getting any answer; in that case, you might respond with something brief like “W9ABCD, ABC1DE what’s the exchange?”, substituting the correct call signs. If it’s simply a serial number (or something similar that you know right away) and signal report, you can jump right in and figure out later where to send the logs. Don’t ask such a question on the air if the remote station is working stations; you almost certainly will annoy everyone involved. If the exchange is only a signal report and a serial number, by listening to a few exchanges you should be able to figure that out quickly enough; if it’s anything much more involved you’ll probably need to look it up somewhere anyway. If the remote station is weak, it may be beneficial to listen to a few exchanges anyway in order to establish the remote station’s transmitted exchange before you try to contact it yourself. A contest QSO is just like any other QSO, only in fast-forward mode. A typical phone contest QSO might go something like this: W9ABCD transmits: W9ABCD CQ contest

N5EFGH transmits: N5EFGH W9ABCD transmits: N5EFGH five-nine, one-four-zero N5EFGH transmits: Five-nine, zero-one-eight W9ABCD transmits: Roger, contest …at which point some other station hopefully responds to W9ABCD, and N5EFGH writes down the QSO in the log and moves on to work the next one. Working a contest by scanning the bands and working stations encountered is called search and pounce, by the way. By only giving the absolute bare necessities, a strong-signal contact can be over in a few seconds. Note that to save time, the signal report for any audible contest signal is usually 59 (or 599 on CW and digital modes). That means that you’ll normally only need to write down the exchange received (since you know your own transmitted exchange). On non-phone modes, the exact traffic will obviously differ slightly from the above example, but the general idea remains the same: getting the particular contest’s exchange well, exchanged, as quickly and efficiently as possible. Tags: procedure (Prev Q) (Next Q), contest (Prev Q) (Next Q)

Q: What if someone responds to my CQ, but I can’t hear him? Tags: procedure (Prev Q) (Next Q), cw (Prev Q) (Next Q) I tried making a CQ on 20 m, 14.060 MHz (the QRP CQ frequency) and parallel to that I had a WebSDR on my computer just to keep an eye on the band. I saw someone responding on the WebSDR, which is rather close to my hometown; however, I couldn’t hear him on my receiver and the signal on the WebSDR was too vague to copy. What should I do in such a situation (apart from improving my receiver)? Should I just send my CQ sequence again and hope the other side understands that I can’t hear him, and stops trying or increases power? Or should I send another sequence to say that I know there is someone, but I can’t copy him? Tags: procedure (Prev Q) (Next Q), cw (Prev Q) (Next Q) User: camil-staps Answer

by phil-frost

Sending simply “?” is sufficient to request the station send his call again. If you want to be a little more verbose, “QRZ?” means “who is calling me?”. If you can copy part of the call you can also respond with the unknown parts replaced with question marks: “AC8? DE MYCALL”. If you are working the QRP calling frequency you should expect most of your contacts to be difficult, and making repeated attempts isn’t unusual. HF conditions can change rapidly, and sometimes all you need to do is wait a minute. It’s not uncommon to send key information (names, calls, locations, RST signal reports) 3 or 5 times if conditions are poor.

If you just can’t make it work, you can try to communicate that. “QRN” (I’m troubled by natural noise), “QRM” (I’m troubled by man-made interference) and “QSB” (I’m troubled by fading) can help you communicate your specific problem, though if conditions are poor it may be futile. In the case of another interfering station, you might “QSY” (change frequency) to some clear frequency. Or, you can just keep calling CQ. It’s not unusual on HF to be unable to make a contact. No one will be offended. The other station will infer that you can’t copy their transmissions and either giver up or increase power, aim a directional antenna, or otherwise attempt to improve conditions. Answer

by andrejako

Well I’d say that there is definitely nothing wrong with just continuing to call CQ. After all, if you didn’t have the SDR hearing the other station, you wouldn’t know that the other guy is there calling you, so there must not be any had feelings for your lack of response. My practical experience here is mostly related to SSB contests, but I think it could apply in your case as well. Normally, when I’m calling CQ and think that I hear another station answering, but I’m not sure, I’d reply with QRZ or partial callsign, if available. Usually it would be something like QRZ? de MYCALL or Question mark Question Mark One Alpha Question mark, this is MYCALL, depending on how well I copied the sign. This way, you may indicate that you did hear something and ask the other station to fill in the blanks. One problem with the QRZ part is that some users may use QRZ instead of CQ and this way the hint may be misunderstood, so do try to send partial callsign if available. If you do reply, and using SDR determine that the other station copied your reply, but is still too weak for you to copy, you may want to make it known to other station that the signal is too weak to be workable. I can’t think of a widely-used Q-code to indicate very weak signal, but some things you could try would be sending QRK 1 and then QRS PSE. QRK is the code for signal readability, with 1 being the lowest grade and QRS is invitation to increase output power. Another alternative that comes to mind would be to send QSA 1 and QRO. The procedure usually lasts until one of the sides of this potential QSO runs out of nerves or if the required contact data are successfully transferred. If you do determine that reading the other station is too difficult, do try to make it known to other stations. Send something like sorry, too weak and continue calling CQ in hope that someone else may respond. Answer

by darryl-wagoner

That is an interesting questions. The only thing I would suggest is ask them to increase power if possible. However if you are not hearing them on your receiver odds are they will not be able to add enough power to copy. You could also send a message of no copy.

If you didn’t have the WebSDR, then you won’t even know someone is calling you. This is the case 100s of times a day. Tags: procedure (Prev Q) (Next Q), cw (Prev Q) (Next Q)

Q: Is there a convention for SSB frequency selection? Tags: procedure (Prev Q) I know that the amateur bands are not channelized. I know that anyone can pick an arbitrary frequency and they’re not wrong, and you are not obligated to have a calibrated VFO. But if everyone picks frequencies at random during a period of heavy usage, there’s likely to be inefficient allocation due to not-quite-wide-enough gaps to fit in. Do there exist, then, any conventions for what frequencies to use, that are more widespread than each individual operator’s idea for best practice? Thinking about this once, I said to myself: SSB is 3 kHz wide, so we can divide that neatly into XXX0000, XXX3000, XXX6000 Hz with only a little bit of waste. More recently while I was operating on Field Day this year, I noticed a lot of people using XXXX500 Hz frequencies, and it occurred to me that if we consider the bandwidth as 2.4 or 2.5 kHz (as it apparently typically is as transmitted, even if receive filters aren’t that sharp) then four channels fit into 10 kHz that way. Is that something people try do? (Reviewing my logs, some but not all of the 500 Hz frequencies fit this pattern.) But trying to spot the pattern this way is an exercise in numerology. Are there any deliberately promoted, or somewhat accepted, schemes for SSB frequency selection? Tags: procedure (Prev Q) User: kevin-reid-ag6yo Answer

by k7peh

I am not sure I understand the question but I will attempt to answer a part of what you are asking. Thinking about this once, I said to myself: SSB is 3 kHz wide, so we can divide that neatly into XXX0000, XXX3000, XXX6000 Hz with only a little bit of waste. No one does that. When you choose a particular frequency for SSB, you usually will look for empty space and that means probably at least 3 KHz distant from other signals. But, not always. As previously stated, if the band is crowded, such as during contests, this 3 KHz rule goes out the window. On modern radios today, many SSB operations will work with filters narrowing down their operating window to maybe 2 KHz. I sometimes have operated at 1.8 KHz since I have a 1.8 KHz roofing filter on my Elecraft K3. Yes, you can understand SSB at 1.8 KHz and it is not quality but who cares for SSB work especially in a contest. Often I will arrange schedules with some buddies for late night 80 meter SSB chats. For

some unusual reason, we have a habit of picking 3767 KHz or something like that. I like the odd numbers because it allows some kind of distance from a lot of regularly scheduled things that have a tendency to chew up the 1 KHz 0 digit (e.g. 3760, 3770, 3780,…). And, if not the 0 mark, they go for the 5 KHz intervals (e.g. 3760, 3765, 3770, 3775,…). So, regularly scheduled nets that can crowd the 80 meter band usually end up on the 0 and 5 1 KHz digit place so I avoid those for my schedules which are not regular. And, when you make a schedule, you always inform the other party (parties) that if not found on such-and-such frequency, scan up 5 to 10 KHz and down 5 to 10 KHz looking. But, no one that I know of has ever planned or thought of channelizing the bands into 3 KHz chunks. No one would obey that rule anyway so it is probably a waste of time. On CW though or other digital modes, anything goes because the average signal width is much less than 1 KHz. In my experience, on the 80 meter band, in the evening hours, no matter where you pick your frequency you are probably stepping on someones skirt or right on top of them. You raise QRL? to find if anyone is there but their answer may not be heard by you even though you may be heard by them so you may likely stomp on them anyway. This is especially true in the range 3900 to 3990 KHz. Answer

by m0lmk

The answer to your question is no. There is not any internationally recognised standard of channelisation on the amatuer radio HF bands when operating SSB. There is a suggested band plan to keep different modes separated and give priority for specific usage but this is only a “gentleman’s agreement”. The standard accepted “good conduct” is to ensure that your transmission is at least 3KHz away from any other that you can hear to avoid causing interference. Answer

by martin-ewing-aa6e

There is no standard, but I note that many SSB stations transmit on an even kHz. I suppose this is just for tuning convenience for those who have accurately calibrated digital VFOs. It’s very easy to scan the band with a 1 kHz step on many rigs. It means you don’t have to fine tune if you’re talking with someone who also has accurate frequency setting. Using 1 kHz steps with ~2.4 kHz bandwidth means there aren’t likely to be big gaps in spectrum usage. (Besides, plenty of people do not use 1 kHz “channels”.) Sure you could pack people more efficiently with a finer step size, but when you consider variable propagation (the “hidden transmitter” problem), things work reasonably well. Tags: procedure (Prev Q)

Diy Questions Q: Can I listen to hams on a standard AM/FM broadcast receiver? Tags: diy (Prev Q) (Next Q), receiver (Prev Q) (Next Q) I am very much out of practice with amateur radio (like many others), so to some, this question may seem obvious. I don’t have any specialised amateur radio equipment, but I do have a Sanyo AM/FM broadcast receiver (240V, 50 Hz, model no. MCD XP630). Is it possible, with minor modification if necessary, to listen to amateur radio enthusiasts using this AM/FM radio? Tags: diy (Prev Q) (Next Q), receiver (Prev Q) (Next Q) User: user17 Answer

by pearsonartphoto

Using this site

, I determined the operating range is:

FM: 87.5 - 108 MHz, AM: 526.5 - 1606.5 KHz The closest ham bands are 144-148 MHz, 1800-2000 kHz. Thus, it cannot receive ham bands without modification. With modification, essentially you need to open the radio and re-tune it’s frequency calibration. There is a website that documents how to do this. It is important that you have a non-digital radio for this to work correctly. Of course, all of this assumes that you are trying to listen to AM or FM signals. You probably could get away with this if you can adjust the FM signal appropriately, although the typical FM broadcast signal is wider band than an FM Amateur Radio signal, but AM signals are rarely used on the HF bands, it’s far more common to use SSB, which a typical AM radio cannot receive, without significant modification. Tags: diy (Prev Q) (Next Q), receiver (Prev Q) (Next Q)

Q: Can two diodes be parallelled in RB to get double the capacitance? Tags: diy (Prev Q) (Next Q) It’s a fact of life that air-gang capacitors , are increasingly more difficult to come by having been superseded by the far more compact varactor diodes. My part of the world components such as the venerable BB212

, MPN3700, MV1662

are almost unheard of at the local stores; anyway I’m only getting started at attempting home-brew. Real VCO stuff will hopefully happen sometime in the future. Basic theory tells me applying multiple capacitors in parallel adds up the effective capacitance a circuit will see. Would I see the same behavior if several make-shift varicaps (say, 1N4007) were connected in parallel? i.e. does capacitance add up using varicaps in a tank that it does for any other capacitor? Tags: diy (Prev Q) (Next Q) User: vu2nhw Answer

by wprecht–ab3ry

The short answer is yes, they do add in parallel. But remember, the Cmin is doubled as well as the Cmax, so the tuning ratio hasn’t changed. Depending on what you are using them for, this may or may not matter. Of course you can offset this with an inductor. Tags: diy (Prev Q) (Next Q)

Q: SDR sampling bandwidth - do the bits per sample matter? Tags: diy (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) I’m looking at data converter chips for a homebrew SDR design, and I see that I can choose not just the sampling frequency, but also the bits per sample. Obviously the sampling frequency has to be several times the target frequency, but what effect does the bits per sample have on the signals I can receive and transmit? Will I be ok with cheaper 8 bit ADC and DAC devices, or will I need to look at 10, 12, or 16 bit converters to experiment with SDR? My primary concern is for HF usage with 200Msps converters and above, with sampling at the antenna, essentially, rather that downconverting, or mixing prior to the sampler. Tags: diy (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) User: adam-davis Answer

by phil-frost

The bits per sample will affect the dynamic range

of your receiver.

There’s a lot of math that I’m sure you can find, but here’s the intuitive explanation: A digital signal can represent only discrete quantities, where an analog signal can represent infinitely many quantities between any two discrete quantities the digital signal might represent. The difference between the actual analog signal, and the represented digital signal, is an error, and is called quantization noise . If you have more bits, the error, and the noise is less. Of course, if there are larger sources

of noise (the preamplifier, ambient RF noise, etc) then the additional noise introduced by quantization doesn’t matter. Thus, it makes sense on as SDR to adjust the preamplifier’s gain so that the noise floor is just above the quantization noise. Otherwise, you are wasting a lot of bits just carrying noise. This maximizes the bits available for actual signal, which is good, because it also maximizes dynamic range, or how much power can be received by the receiver before it clips (the digital signal can represent a signal only so big). This is of particular concern for SDRs because of their wide receive bandwidth: you may not be listening to that guy with the S9+ signal, but your receiver is. If that signal is strong enough to hit the limits of your ADC, then you get clipping, which will introduce harmonics all over the band, making you unhappy. You could turn down the receiver’s gain, but then the very weak DX station that is just above the RF noise floor will be below the quantization noise. The resolution (number of bits) for the DAC is not really as critical, since you don’t need a lot of dynamic range to transmit. You will still have quantization noise, but if the transmitter gain is set to use the full range of the DAC, that noise will be way, way below your transmitted signal. So, 8 bits is more than sufficient for experimentation, but this is definitely a “more is better” situation. It all depends on the performance you require, and also your ability to build the rest of the receiver to utilize the full capabilities of the ADC. Answer

by pyhazard

The number of bits in the converter will set the maximum dynamic range of the resulting data stream. This is approximately SNR = 6 dB × Bits + 4.8 dB (for a full scale input sine wave). However, as with everything in life, this is only the beginning of the story. The data sheets for the converters will typically list the SNR achievable with the chip when used in the most efficient manner. For fast, larger bit sized converters, this is almost always less than the SNR shown above, so bit size becomes much less critical than the rated SNR at the operating point you expect. In addition, since you appear to be leaning towards the faster wide-band ADCs, I will assume you are interested in block processing of entire bands. In this situation the SFDR , or spurious free dynamic range, is important since large signals may end up covering up small signals on other bands or other regions of the band. This is often less than the SNR spec and may be your limiting factor. At the heart of your question was “How do I choose the bit size of my converter?” Well, the simplest answer is that you must match it to the dynamic range of your RF front end output, meaning to make sure your P1 dB or saturation point is near the top of your ADC’s range and the noise floor is less than SNR below that. So far I have only spoken of ADC’s. For the DAC’s you do not have to worry much about the quantization noise since you will be following your DAC output with a filter. For the DAC the number of bits will set your dynamic range, of course; however, you do not have the near signal-far signal dynamic range problem so the bits are much less important. The SFDR is still very important since you do not want to send spurs out or have to manage

them. Tags: diy (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q)

Q: How do I extend broken coaxial cable? Tags: diy (Prev Q) (Next Q), coaxial-cable (Prev Q) (Next Q) I have a piece of 75 ohm coaxial cable of unknown type (outer diameter is around 7 mm) which has developed a breakage in the center conductor (which is stranded). This cable is an adapter cable which connects my RG-6 type coaxial cable to my RTL-SDR card. As far as I understand, the best way to solve the issue would be to simply replace the cable with another cable of higher quality. Unfortunately, this solution is not applicable to me, since the ends of the cable are attached to connectors of types which I can’t easily obtain. The card end uses MCX connector and the RG-6 end uses a type of Belling-Lee connector suited for work with thin coaxial cables. Second idea that came to me and which I used with success with some other coaxial cables is to cut out the middle, damaged, section and leave short pieces of cable near the connectors I can’t replace. After that, connect easily obtainable connectors to the healthy ends of the cable and mate the new connectors or use another coaxial cable in the middle. SMA and RP-SMA connectors come to my mind here, but the problem is that they are 50 ohm connectors in general. I also don’t have the tools to install them and this one-off repair doesn’t justify obtaining such tools. Another idea that I like the least but am currently most likely going to go with would be to directly connect the two healthy ends of the cable. Solder together the inner conductors, cover the joint with heatshink tube, then carefully solder together outer braided conductors and cover them in heatshrink tube as well. Problem here is that I don’t like the reliability of the resulting work. A variation of this theme would be to solder the healthy ends of the existing cable to a new piece of a different, but similar, coaxial cable. The effect of this is that I’d have more room to work with. Finally the worst solution I see right now would be to replace the connector on the card which uses the damaged coaxial cable with an SMA connector. The problem with this is that SMA connectors are in general 50 ohm connectors and this is a 75 ohm system. So my question is basically how do I repair this cable? Which of the options I could work with is the least bad and are there any better ideas I didn’t think of? Tags: diy (Prev Q) (Next Q), coaxial-cable (Prev Q) (Next Q) User: andrejako Answer

by wprecht–ab3ry

A complete replacement will be the most reliable solution. Baring that, replacement of one end if the resulting size is acceptable. I would rate a manual repair dead last. Soldered joints are rigid and even if the repair holds, it will place stress on adjacent sections of

coax. These connectors and in fact, complete cables with MCX on one end and a Belling-Lee connector on the other are available, inexpensively, on eBay. One UK shop lists them all: . They cost from about 2.00USD for the ends to about 10.00USD for the whole cable. Tags: diy (Prev Q) (Next Q), coaxial-cable (Prev Q) (Next Q)

Q: Dummy load construction and heat dissipation Tags: diy (Prev Q) (Next Q), equipment-design (Next Q), dummy-load (Next Q) I’m building my own dummy load, consisting of resistors submerged in liquid paraffin (or something similar, not 100% decided). I had some questions around heat dissipation and how I can calculate and avoid the thing over-heating. 1. Is there a particular fluid that is better than other in both performance and cost? 2. What sort of volume of fluid should I use assuming I would be using up to 100W, such that it won’t start heating up quickly? Is there even a way to accurately calculate this? 3. Are there any non-obvious safety concerns I need to think about when constructing and using this? I don’t want to miss anything simple but obscure. 4. In a sealed system like this, is there any risk of explosion due to pressure from the liquid heating? Tags: diy (Prev Q) (Next Q), equipment-design (Next Q), dummy-load (Next Q) User: david-vk2vxk Answer

by phil-frost

Is there a particular fluid that is better than other in both performance and cost? Water is hard to beat in both respects . The trouble is it has this tendency to become a conductor as it dissolves salts, so it must be insulated, or somehow kept very pure. Sometimes the trouble of this is too much, so some sort of oil is easier. What sort of volume of fluid should I use assuming I would be using up to 100W, such that it won’t start heating up quickly? Is there even a way to accurately calculate this? Heat capacity is perhaps the relevant physical property here. The specific heat capacity of liquid water is about 4.8J/(gK) , and since 1mL of water weighs about 1g, we can also say the volumetric heat capacity of liquid water is about 4.8J/(mLK) . We know that W = 1J/s , and from these two things, given a power, and some volume of water, we can

calculate at what rate the temperature will rise, if the temperature is uniform throughout, and no heat energy is being lost elsewhere. Let’s use 100W and 1L as an example: 100 J s

mL K 4.8 J

1 1000 mL

= 0.21

K s

Since we are talking about a rate of change, you might as well consider K = ∘ C . Of course, this involves two assumptions we know to not be true, the first being that the temperature of the water (or whatever coolant) is uniform everywhere. If the coolant is actively stirred, then it might be close enough to true. Otherwise, you are dependent on conductive currents and conduction to distribute the heat energy throughout the coolant, some parts are hotter and some are cooler, but the average temperature increases at this rate. But this is somewhat moot, given the second assumption: that no heat energy is otherwise being lost. Probably you won’t wrap the dummy load in blankets then operate it until it overheats, but rather construct it with a surface designed to radiate heat into the ambient environment well enough that it can be operated indefinitely without overheating. The job of the coolant is really just to provide a good thermal coupling between the heat sink and the heat sources, and to average out any transient thermal loads. The relevant physical property for the heatsink is absolute thermal resistance . This quantity has units K/W and tells you, for a given constant power, what the temperature increase above ambient will be. It will be specified by the manufacturer’s datasheet. You also need to add to this the thermal resistance of everything between the heat sources and the heat sink. Unfortunately calculating the absolute thermal resistance of your tank of coolant is hard, because it has a complex geometry, and the things likely to be used in the tank (water, oil) are actually not especially good thermal conductors: they move the heat around mostly by convection. So, the general approach is this: figure out, for your design power and allowable temperature rise, how big the heatsink would need to be assuming the best case, then make it bigger to account for other factors. TLAR is probably the most economical method, and if you need something more precise, then pump a known power into a prototype, and if it gets too hot, make it bigger. Are there any non-obvious safety concerns I need to think about when constructing and using this? I don’t want to miss anything simple but obscure. Besides the obvious ones of having a potentially large quantity of possibly flammable, probably very hot fluid, potentially heated beyond its boiling point, connected to an electrical energy source that might be capable of generating sparks or heating (especially under fault conditions) materials above said fluid’s flash point? No, I can’t really think of any. I don’t think it’s the non-obvious safety concerns that are going to kill you. In a sealed system like this, is there any risk of explosion due to pressure from the liquid heating?

Very yes, see last question. I wouldn’t seal it if I could help it, and if I did, I’d be sure it wasn’t sealed very well, so an overpressure fault would just dribble rather than explode. Also couldn’t hurt to make sure the pressure release mechanism indeed dribbles and not shoots a hot jet of oil. Tags: diy (Prev Q) (Next Q), equipment-design (Next Q), dummy-load (Next Q)

Q: RF Transceiver for walkie talkie use Tags: diy (Prev Q) (Next Q), uhf (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q) I’m close to my EE. BSc finale and I’m looking to play around a little bit with the stuff I’ve learned. To be honest, I’m a little bit upset that after 4 years of learning communications theory, I’m not able to choose the hardware I need. My idea is to build a half-duplex walkie-talkie with the following reqs: Low voltage operation. Till 5V. Range about 1.5 km LOS. ISM frequency use. (I prefer 433 MHZ UHF bands.) Single chip that doesn’t require extra elements such as crystal or filters. The idea is to install 2 walkie-talkies, one on each house. House are about 900m range. One has a direct window outside while the other is an interior office. The application is for voice only. Considering the FM advantages I’ll prefer it, but if there is a big difference of value then AM could be an option. The chip I’m looking for must be the smallest that can be. I’ve seen many chips (such as the following links) but I’m not sure that their digital buffers support voice applications.—Sensing/RFIC-Transceivers-27-to950MHz/TH7122-121.aspx Tags: diy (Prev Q) (Next Q), uhf (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q) User: santiago Answer

by adam-davis

The chip you’ve linked is capable of analog FM transmission and reception, from 2.5kHz to 80kHz bandwidth. In the frequency range you’re looking at it has a frequency resolution of 12.5kHz. It’s very low power, with the right antenna it should reach your target LOS. Check out Figure 4.2 in the TH7122 and TH71221 Cookbook for an example showing how to use the chip as an analog FM transmitter, and figure 6.7 for an example of how to use it as an FM receiver. By combining the two circuits with the typical application circuit you can build a single-chip analog FM transceiver. Note that your requirement, “Single chip that doesn’t require extra elements as crystal or filters” is going to be hard to meet with any radio design. There are several inductors and capacitors used as filters outside most “single chip” transceivers. If you want any frequency stability you’re going to need a crystal. The Philips SA58646 is also a good choice, but again you’re going to have to deal with a few inductors, capacitors, and a crystal.

Also note that with such low power devices your antennas are going to have to be very, very good, and probably very large. If you don’t want to spend a lot of time and effort on antennas, or need small antennas, then you’ll have to trade off some additional effort adding an RF amplifier to these devices and consuming more power. Are you sure you don’t simply want an off-the-shelf transceiver ? If you’re trying to avoid filters and crystals while building your own transceiver, it seems you might need a higher level solution than a DIY circuit. The radio linked is a cheap HT for the UHF band, runs on 3.7V, and has a 3W output. It’s under $20, and if you remove the battery, casing, controls, connectors, then the one or two PCBs that are left are very small. It does appear to have a low power TX setting, so you should be able to set it to 1W output rather than the full output power if you have power consumption concerns beyond requiring low voltage. You may even consider modifying the radio to remove the PA and use the very low output prior to the PA, saving significantly more power. Tags: diy (Prev Q) (Next Q), uhf (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q)

Q: Low parts count CW HF receiver? Tags: diy (Prev Q) (Next Q), receiver (Prev Q) (Next Q) I’d like to be able to provide my kids with the opportunity to build something a little better than a passive crystal set, but still very, very simple in terms of individual electronic parts count. It seems to me that a CW receiver should be the easiest type to build, if I’m incorrect and an AM is easier, or just as easy, let me know. What is the lowest parts count receiver one can build that covers some portion of the HF spectrum likely to have CW signals in it? I’d prefer low cost parts, but low parts count is still the most important requirement. Ideally it could be breadboarded, but point to point wiring is fine. It doesn’t have to be great audio quality, or even very selective and immune to noise. It just needs to be able to pick up enough of a signal that a careful listener will notice the CW in the static. Is there a receiver design that needs 20 parts or less? 10 parts? Fewer? Tags: diy (Prev Q) (Next Q), receiver (Prev Q) (Next Q) User: adam-davis Answer

by hotpaw2

For CW, a simple regenerative receiver will produce an audio sidetone. Such radios were actually usable and used by radio hobbyists to receive HF CW. So I would search for a design of a 2 transistor regenerative receiver (2nd transistor used to isolate or drive some headphones) in vintage hobby electronic magazines and kits dating from the earliest decade of the availability of transistors to hobbyists. Probably somewhere between 10 and 20 parts, depending on how you count them. You might have to wind your own inductor

coil(s). Tags: diy (Prev Q) (Next Q), receiver (Prev Q) (Next Q)

Q: What is the expected microphone input voltage level of a handheld transceiver? Tags: diy (Prev Q) (Next Q), ht (Prev Q) (Next Q), cw (Prev Q) (Next Q) Ok, so I’m looking to inject some computer generated CW into a little handheld rig by wiring direct into the mic input line. What sort of voltage is expected on this input, are we talking uV, mV or even Volts? Tags: diy (Prev Q) (Next Q), ht (Prev Q) (Next Q), cw (Prev Q) (Next Q) User: m0atz Answer

by wprecht–ab3ry

In general you are talking volts. But it’s different for each make of radio and even different models of the same brand. You might want to start researching here , the link contains a vast amount of information about microphone pinouts and links to even more information. I know you mentioned you are hacking what’s probably a cheap Chinese HT, but this source will give you some idea. Next, connecting the computer directly to the radio, without some form of isolation is a Bad Idea (tm). It’s doable for short tests, but you’ll introduce noise and the possibility of ground loops, etc. They make cheap audio transformers for just such a purpose, plus they are useful for my next point. PC speakers and mics are generally very low impedance, like 4 or 8 Ohms. Radio mikes are all over the place on impedance, but frequently 600 Ohms. So you’ll need a transformer to match that anyways, once you determine the impedance of the microphone, you can select the right value. Answer

by adam-davis

A very simple adaptor can be built as follows:

You can increase R1 to lower the signal level at the microphone output, or decrease R1 to raise the signal level. While some use potentiometers to make adjustments easier, I’ve

found they are a frustrating source of noise and failure in such circuits, and suggest that, if used, they should be used only to find an appropriate level, then measured and replaced with a fixed resister. C1 can be between 1uF and 4.7uF for audio level signals, but if you’re trying to pass very high frequency signals you might stay on the lower end of that. While C1 will help reduce ground loop problems, you may still experience them, particularly if the radio is located far from the computer, or attached to a different power source than the computer. The use of an audio isolation transformer can be helpful with this. Impedance matching isn’t necessary since the microphone impedance is significantly larger than the speaker output, and we’re not trying to transfer significant power. The only worry one might consider is whether the speaker output will be damaged with a high impedance. My experience with most PC sound cards suggests that there’s nothing to worry about, but you can place a low value resister in parallel with this circuit on the speaker output if it concerns you. The values as suggested will probably provide more volume than needed. This only drops about 30dB, whereas I’d expect a 40dB drop is needed for a speaker output to microphone input. However, this is intentional, and allows further volume control to occur on the computer. Again, increase R1 by doubling it each time if you find this too “loud”. A 1Mohm resistor in R1 would give about a 40dB drop. Tags: diy (Prev Q) (Next Q), ht (Prev Q) (Next Q), cw (Prev Q) (Next Q)

Q: Replacing hand-wound inductors with store-bought versions Tags: diy (Prev Q) I’m wading through some schematics for a direct conversion I-Q SDR receiver, and there is an L-C band-pass filter on the input. Each inductor is specified by an inductance, a toroidal core material, a wire gauge (AWG), and a number of turns. I understand that this is all the information that is required to replicate the exact specified inductor (and all the values check out), and I know I could replicate the part described in the schematic. However, I would like to avoid manually building a component like an inductor if I can ( because of logistics and personal enjoyment). While I can certainly select an inductance value from a menu on Digikey, there is more to inductors than just the value. I suspect the self-resonant frequency (SRF) needs to be well above the frequency of interest, and the Q of the inductor should be high, but past that I’m not sure what is important. What problems am I going to run into if I switch from hand-wound toroidal inductors to a “store-bought” inductor such as this one ? Tags: diy (Prev Q) User: w5vo Answer

by phil-frost

I’m going to say a lot of stuff that could go wrong, but really, don’t be discouraged. I think mostly ham equipment is built with self-wound inductors because cores and magnet wire is cheap and easy to source. Take apart a cell phone and you may not find a single wound inductor on it. None of the problems to follow are insurmountable, if they are even problems at all. Of course, it always depends on the application and circuit. You are right to care about the self-resonant frequency and Q. Generally a high SRF and Q is good, but in some circuits it may be a problem merely that they are different, if the design already compensates for the non-ideal components of the self-wound part. Probably not an issue except in the most critical filters, and probably nothing that can’t be fixed by adjusting a capacitor or resistor to compensate. This is why high SRF and Q are desirable: you can always make them lower by adding parts, but you can’t make them higher. All ferrite-cored inductors get lossier with increasing frequency. Generally, ferrites for low frequencies can provide a higher permeability (thus increasing inductance per turn), but as frequencies increase so do losses, necessitating lower loss ferrite materials with a lower permeability. How does one read a ferrite datasheet? gives some insight into the parameters of the ferrite itself. So, also check the intended frequency of operation for your considered chip inductor. If the datasheet doesn’t say otherwise, you can assume that the test frequency is near the top of frequencies for which the part is suited. You could go a little higher if you don’t much care about losses or Q. If you go a lot higher you might as well buy a resistor. Other problems you might encounter, generally: Reduced power handling The smaller surface area of a chip inductor makes it less able to radiate heat, and its smaller mass makes it heat more quickly for a given power. Probably a non-issue for receive filters, maybe an issue for transmit filters. Lower saturation current Again driven by smallness, chip inductors will typically have less ferrite material per ampere-turn of wire in it, which increases inductance per physical size, but decreases saturation current. Besides the possibility of outright saturating the core, you can probably measure higher non-linear distortion in a chip inductor with the right equipment. This is because saturation isn’t a hard wall, but something that sets in gradually. The less magnetized the core is, the more linear it is. If the core is made smaller but inductance is held constant, the core must be more magnetized, and thus less linear. The difference may be slight, and not important for many applications. Higher ohmic losses The smaller size of surface mount components usually dictates smaller conductors, which have higher resistance, and thus higher loss and lower Q. More leakage (in some designs)

Some, but not all chip inductors do not have a closed magnetic circuit. This can lead to mutual inductance with others on the board, making transformers where you don’t want them. Read the datasheet to see what you are getting. The example you provided says it is “magnetically shielded”, suggesting a closed magnetic circuit. Tags: diy (Prev Q)

Digital Questions Q: How do I discover APRS coverage? Tags: digital (Prev Q) (Next Q), power (Prev Q) (Next Q), packet (Prev Q) (Next Q) I’m considering adding simple APRS transmitters to my vehicles. I’d rather just put one in and forget about it, but I understand there are areas of the US where a stronger transmitter would be required to successfully send an APRS update packet. Are there coverage maps, similar to cell phone maps, which will help me understand where APRS should work and where it might not? How powerful an APRS transmitter do I need to get approximately 75% coverage in the US? Tags: digital (Prev Q) (Next Q), power (Prev Q) (Next Q), packet (Prev Q) (Next Q) User: adam-davis Answer

by dan-kd2ee

Coverage maps are a thing that is notoriously difficult to do right. There are some very complex programs (Radio Mobile is the one I know the most about) which can generate coverage maps if you’re prepared to wade through the technical details and the quirks of the software. Unfortunately it’s not as easy as drawing a circle of a certain size around each digipeater. Furthermore, power isn’t the only factor - 5W vs 30W isn’t going to make any difference at all compared to the night-and-day difference between an NMO-mounted mobile antenna vs an HT laying across your passenger seat. You can use the maps (warning: uses a google map overlay, it can be slow on some computers) to see all APRS activity. There’s a button along the top right allowing you to filter out everything except APRS stations or digipeaters. You’ll see that there are areas of very dense coverage - I’m looking right now at Baltimore, Philadelphia, up the NJ turnpike to NYC, and along the coast - but then there are wide areas that are empty, either because there are no digipeaters, or simply no one has sent a packet from there in the past 24 hours. An HT connected to a real mobile antenna, properly mounted on your vehicle, is equal to or better than 90% of the users you’re seeing on that page, so if you use that setup you will get coverage anywhere that you see other users getting coverage on that page, with the possible exception of the outskirts of less heavily populated areas. You could do better by using a 50W mobile, but even that is only a 10dB improvement and will only extend the coverage areas by a few more tens of miles, it will not magically give you coverage in the “dead spots” on that map. You also often do not want to run maximum power on something digital like APRS anyway unless it’s a radio specifically intended for it - running “at the limit” can make your transmitted signal more dependent

on the whims and quirks of the final amplifier, which can introduce nonlinearities which actually make your signal harder to decode. Plus, if you’re signal is so powerful that digipeaters can hear you but you can’t hear them, you risk stepping on signals that you can’t hear, meaning that not only will you not get repeated, whoever you stepped on won’t get repeated either. Tags: digital (Prev Q) (Next Q), power (Prev Q) (Next Q), packet (Prev Q) (Next Q)

Q: 2m or 70cm FM mobile radio for digital mode operation Tags: digital (Prev Q) (Next Q), uhf (Prev Q) (Next Q) Are there any 2m and/or 440cm FM mobile radios that have audio inputs for supporting digital modes, like PSK31 or SSTV? I have a Rigblaster that I use with my HF radio so I could get a mike cable and connect it directly to the mike input in the same way, but is there any VHF/UHF radio available that has better options for connectivity for working digital modes on VHF/UHF? Tags: digital (Prev Q) (Next Q), uhf (Prev Q) (Next Q) User: kevin-hooke-kk6dct Answer

by oh7lzb

Most modern VHF/UHF FM mobile rigs designed for Amateur Radio use have a “data” connector on the back. Currently manufactured dual-band examples include Yaesu FT-7900, Kenwood TM-V71, Icom IC-208H - they all have the same 6-pin miniDIN “data” connector using the same main pinout. The 6-pin data connector is originally designed for attaching packet radio TNCs and other data equipment, and usually has at least the following pins: Ground TX audio in (transmitted audio) PTT (ground to transmit) RX audio out, “1200 bit/s” “normal audio” RX audio out, “9600 bit/s” discriminator output I quoted the bit rates, since the radio documentation often cites these standard packet radio speeds, although in reality it’s just audio, and the radio doesn’t really care about any bit rates as such. The “9600” pin audio output is taken before audio filter/amplifier stages of the radio, and has a flatter audio frequency response that is good for high speed data such as 9600 bit/s packet or AIS reception. Technically, you can run SSTV or PSK31 over FM, and that “data” connector will suit that purpose perfectly. But it’s not overly popular in most areas, so you might have to talk some friends to play with it. Most of SSTV and PSK31 activity is on HF SSB, although VHF/UHF digital chat as such should be a lot of fun.

PSK31 over FM in particular is quite strange and unusual, since PSK31 is designed to be a very narrow-bandwidth (31.25 Hz) mode for SSB transceivers, and transmitting it over FM (some 20 KHz) would be a waste of perfectly good radio spectrum and transmitter power. It works, but it’s not efficient. Then again, it might be fun, and if you live in an area where most of 70cm is almost completely quiet and inactive (like I do), a little inefficiency on an irregular basis is not going to do harm, if you’re having fun. A lot of amateur FM voice communications don’t have a lot of useful information content, either. SSTV isn’t so narrow (about 3 kHz), and there have been more or less official FM channel allocations for it. Some US web sites cite VHF/UHF SSTV AFSK FM calling frequencies. IARU Region 1 (Europe) SSTV(FM/AFSK) frequency for 70 cm is currently 433.400. I also often use the “data” connector of my FT-7800 for recording received voice communications on a computer. Works fine. Answer

by dan-kd2ee

Sure, most radios have the ability to patch in audio. If it isn’t through the front microphone connector, it’s through an accessory connector, which is available on every commercial radio I’m aware of - although perhaps only on a few amateur mobiles. But why would you want to? SSTV and PSK31 cannot be reasonably transmitted over FM. FM transmits a carrier at a single frequency that is modulated. That is not the same as the SSB that is used in HF transceivers for digital mode operation - it’s a completely different kind of modulation. In SSB, the bandwidth actually occupied by the output signal is equal to the bandwith occupied by the input signal - so if your input audio shifts by 31.25Hz, your output RF shifts by 31.25Hz. In FM, every input signal uses up the entire channel width. You couldn’t use something like fldigi to receive multiple PSK31 signals in the same FM channel at once, because your FM receiver is physically incapable of receiving and demodulating more than one signal at a time. You would effectively be taking up an entire FM channel but only using less than one percent of it. SSTV operates in a similar way. The properties of FM do not allow for use of digital modes in the same way as SSB does. If you want to use digital in VHF/UHF, you need either an SSB transceiver (might be available for 2 meters?) or a digital radio (using D-STAR, TRBO, or something else) or an SDR (a software defined radio may allow the necessary types of operation). There are a few modes that sacrifice radio efficiency in exchange for simplicity, such as APRS, however APRS has much shorter transmit durations than PSK31 allowing for the frequency to be shared (I’ve seen operators with an active PSK31 signal for over a minute, imagine the APRS pileup if every station in range was forced to wait that long for an open carrier). The root of the difference is that PSK31 - very small bandwidth but very slow was designed for Frequency Division Multiple Access (FDMA), while APRS was designed for Time Division Multiple Access (TDMA) all on the same frequency. If you’ll excuse a few signal processing terms, SSB as a modulation scheme is a linear function - that means that adding two audio signals together and passing it through SSB results in the same thing as if the audio signals had been encoded individually - whereas FM is not. This interesting property of SSB is what makes it possible to receive more than

one signal at once. Linear modulation schemes like SSB preserve FDMA as well as TDMA, however nonlinear modulation schemes like FM preserve only TDMA, and not FDMA. References: Why PSK31 over FM is nonsense “FM only…is NOT a popular PSK mode “PSK31 would [lose] most of its benefits if run thru an FM system. Certainly it would no longer be narrow band. PSK31 via a 2M SSB system would be a good weak signal mode. “Using PSK31 over FM results in [losing] most of the benefits of PSK31. You are still transmitting a wide FM signal and the threshold needed by the FM receiver still requires the same signal level as voice FM. “on FM? It would defeat the purpose of PSK31.” Tags: digital (Prev Q) (Next Q), uhf (Prev Q) (Next Q)

Q: Store-and-forward capable satellites in operation? Tags: digital (Prev Q) (Next Q), satellites (Prev Q) (Next Q) The amateur satellite community used to have a small fleet of pacsat satellites (AO-16 and friends), which were capable of store-and-forward message passing: you could upload messages to the LEO satellite on one side of the world, and download the message once the satellite has travelled to the other side. 1200 bit/s BPSK on 2m/70cm. At the time, as a kid, I didn’t have the budget to set up a ground station for them. Are any amateur satellites with digital store-and-forward capability in usable status these days? It might be fun to try them out. Tags: digital (Prev Q) (Next Q), satellites (Prev Q) (Next Q) User: oh7lzb Answer

by adam-davis

Some otherwise operational amateur radio satellites have store and forward, however none of them appear to have store and forward enabled or working at this time: AO-7 AO-7 , launched in 1974, included a store and forward message unit, Codestore, cablae of storing and repeatedly retransmitting 18-word Morse code messages loaded by ground stations. It’s the same design as was flown on OSCAR 6 . The unit is not currently in use, and it’s unclear if it’s still operational, though many other parts of AO-7 are still functioning.

FO-29 (JAS-2) FO-29

, launched in 1996, included a digital BBS that is not longer operational.

You can find a list of operating Amateur Radio satellites on Wikipedia, and searching their names will bring up sites that show their capability. There is also a list of Amateur Radio satellites, including cubesats, and on the SatBlog which may prove useful. Also note that another launch of many cubesats is occurring at the end of November, 2013, and some of these satellites may have store and forward. Keep in mind that cubesats are very often short-lived without altitude or attitude control, so you will want to focus on the OSCAR satellites that are still operational. Tags: digital (Prev Q) (Next Q), satellites (Prev Q) (Next Q)

Q: Can an amateur use cellular technologies with SDR? Tags: digital (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q), rtl-sdr (Next Q) Software Defined Radio is opening up many new possibilities for amateur digital modes. One family of technologies that interests me is cellular. 2G GSM voice/sms and 2.5G GPRS data has been proven to work with OpenBTS on a USRP SDR using licensed cellular bands. Can this technology be used by amateurs? Could an amateur cellular network be deployed sometime in the future? Note: I know that there are many small practical considerations to doing this. Cellular technologies are heavily patented, but patents on many older GSM technologies have recently expired. Also, some deployment tweaks will be needed to adhere to amateur regulations, such as disabling encryption. Answers should focus on the fundamentals of amateurs using cellular technologies via sdr and not these small hangups. Tags: digital (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q), rtl-sdr (Next Q) User: jc-hulce Answer

by adam-davis

Yes it can be done, and there are some huge advantages: Better use of bandwidth Existing chipsets/support/implementation Low power In fact there’s little reason why one couldn’t essentially replace DSTAR and competing systems with a standard based on GSM and GPRS technologies. Even for those parts that are patented, the patents running out means we’d be using technology that’s advanced well beyond DSTAR and similar systems, and it’s completely open. It would take a few individuals building up an example design and example infrastructure for it to be picked up widely. But once that happened you could build a cellular network over Amatuer Radio frequencies, and you could expand functionality to support specific Amateur Radio needs such as public safety and emergency communications. Answer

by pearsonartphoto

Honestly, the key technology to making this work has been around for quite a while, and that is the phone patch. Essentially, you can get on a repeater and dial a person from said repeater. The area of operations is fairly limited for such, but it has been done. And an SDR might help with this process, but it isn’t required. As far as digital, the key thing to remember is that Amateur bands prohibit encryption. Most of the useful things that one does over a cellular network require encryption of some form. Thus, it isn’t likely to be of huge use. But yes, in principal it could be done.

Tags: digital (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q), rtl-sdr (Next Q)

Q: Is there a disadvantage to using a cheap HT for APRS? Tags: digital (Prev Q) (Next Q), ht (Prev Q) (Next Q) Looking to build a cheap (not even inexpensive, just dirt cheap) APRS beacon. Right now you can get a dual band handheld transceiver with rechargeable battery, antenna, etc for under $31 [USD], for instance. I can’t find a cheaper transceiver. What are the downsides to using a BaoFeng, Wouxun, or similar cheap HT for APRS? Are there ways to mitigate the problems, if any, of these units? Tags: digital (Prev Q) (Next Q), ht (Prev Q) (Next Q) User: adam-davis Answer

by amber

Most of the common disadvantages for Baofengs et al have to do with usability (e.g. poor user interface, odd squelch performance). The actual reception and transmission power is just fine. The majority of the disadvantages are negated when working with APRS, since it’s the APRS modem interacting with the radio rather than a human being. The main thing you’d probably still want to be aware of is the antennas; most of the cheap HTs come with poor-performing rubber duck antennas. Replacing the antenna is probably a good thing to plan for if you go with one of them, to help get a more reasonable signal strength. Answer

by oh7lzb

Some of the cheap HTs, which were designed for voice, key up the transmitter quite slowly, and the transmitter also stays on for quite a while after the PTT is released. At least my older Puxings behave this way - they require a long txdelay in the tracker (delay from PTT down to the start of data transmission), and there’s also a long “tail” after the data. It might have to do with power saving methods, which can be disabled in radios which were designed for data (like the ham rigs with built-in APRS). You can compare transmitter key-up/key-down timings by attaching another receiver to a computer, opening the squelch completely, and recording the APRS transmissions using a wave editor such as Audacity (free). Zoom in to the start of the transmission - it’ll be quite easy to see where the txdelay flags end and actual data starts. If your tracker has a txdelay setting of 20 (200 ms - they’re traditionally set in 10s of milliseconds), and you’re seeing 50 ms of flags before data, the transmitter takes 150 ms to transmit. If you’re seeing 150 ms of flags before data, the transmitter only takes 50 ms to wake up. On some of these SDR-based HTs the delay varies a lot.

Zoom in to the end of the transmission and see how long the transmitter transmits after the end of data, too. Some stay on longer, wasting more bandwidth than others for the same amount of transmitted data. Tags: digital (Prev Q) (Next Q), ht (Prev Q) (Next Q)

Q: How to calculate UMTS bitrates? Tags: digital (Prev Q) (Next Q) Assuming: Radio frame 1. Subdivided in 15 slots 2. Number of chips: 38.400 3. Duration: 10 ms; each slots = 666.6 μs and has 2.560 chips Example of channels DPDCH (Dedicated Physical Data Channel) (UL) Spreading factor varies between 4 and 256 Data rates 960, 480, 240, 120, 60, 30 and 15 kbit/s Spreading factor 4, 640 bits/slot, 15 slots/frame, 100 frames/s -> 960 kbit/s Spreading factor 256, 640 bits/slot, 15 slots/frame, 100 frames/s ->15 kbit/s A connection can have at most 6 DPDCH -> 5, 74 Mbit/s Question I don’t really understand how the bitrate for DPDCH is determined like “960kbit/s” for example. Which formula is used to derive these values? Here is a picture of the frame structure.

Tags: digital (Prev Q) (Next Q) User: beginningperl Answer

by phil-frost

Spreading factor 4, 640 bits/slot, 15 slots/frame, 100 frames/s = 960 kbit/s I don’t really understand how the bandwidth for DPDCH is determined like “960kbit/s” for example. There’s no equation. It’s just another way of stating the information that’s already there. By dimensional analysis : 640 b 15 slot 100 frame 1 k 960 kb = s 1000 s slot frame I also would not call “960 kbit/s” a bandwidth. That may be acceptable in the context of say, a PCI bus, but in the context of a radio protocol, bandwidth also means the width of the signal in the frequency domain. I’d call it a bitrate to avoid that confusion. Tags: digital (Prev Q) (Next Q)

Q: LOS One-way radio system, 4km with at least 1000bytes/s Tags: digital (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q)

In order to track skydivers/BASE-jumpers with flysight I am looking for a one-way radio system to transmit the location data. System needs the following specifications: Skip code block Frequency: Not important, preferable legal (Europe) Bandwidth 1000 bytes per second (at least) Range: 4000 meters Line of Sight Yes Latency As little as possible Mobile Coverage Not available Transmitter - Location Air - Movement Moving, up to 200 km/h horizontal groundspeed vertical distance: closing towards receiver during operation - Interface USB or serial - Weight As little as possible - Size As small as possible Receiver - Location Ground - Movement Stationary during operation, movable by car - Interface Not important, what ever works - Weight Not important, movable by car - Size Not important, movable by car

Any suggestions? Tags: digital (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q) User: wittrup Answer

by benswayne

There are a number of commercially available RF data modems that operate within the amateur radio spectrum for hobby use particularly with RC (remote controlled) hobby aircraft. However, I believe your specific ITU Region imposes additional output power limitations which will make this challenging at 4 km distance. The RFD900 developed by an Australian company is sold in the USA by jDrones for hobby RC use and will support ranges up to 40km and data rates up to 250 kbps! However please note these specs are inversely related and subject to the limitations of your antenna system and the environment (more speed closer, slower data rate further away). Line of sight open air 4 km should be no problem at all with the data rates you are talking about. This particular model outputs 1 watt in the 902 Mhz to 928 Mhz frequency range otherwise known as the 33cm band in ITU Region 2 (Americas) . However, it appears this band is not allocated in Europe (ITU Region 1) and may exceed your maximum output power limits - so you may not be able to use this specific model of hobby radio modem in your location. This is simply the only one I know because I am in Canada. For Europe you should look for a comparable model in the 70cm (433 Mhz) band such as the PipX (only 100 mw). However the additional limitation on output power may limit operational range. In that case you may need to look into building an antenna tracker for use with a highly directional antenna such as a yagi . This involves transmitting the GPS co-ordinates down the link and having the antenna tracker point the antenna straight at the target. This may be somewhat experimental if you are moving at 200 km/h - I think you will need to custom build your antenna tracker, perhaps taking into account the average falling speed

and any latency in the motor controller and anticipating the targets future position. Eitherway, experimentation is part of the hobby of amateur radio! So if you do decide to take this on, publish your project progress somewhere for all to enjoy. Tags: digital (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q)

Q: Efficient BPSK31 amplification Tags: digital (Prev Q), amplifier (Prev Q) (Next Q) I’m looking at making a portable system that can transmit BPSK31. I have a limited power budget, so I’m looking at trying to make my final power amplifier as efficient as possible. From my understanding, you can’t use a plain non-linear amplifier (e.g. Class C or E) because BPSK31 isn’t a constant envelope signal. The amplitude drops to zero on bit changes, and that behavior prevents splatter on bit changes. Is there a way to efficiently amplify BPSK31, or am I stuck with an inefficient final amplifier? Tags: digital (Prev Q), amplifier (Prev Q) (Next Q) User: w5vo Answer

by phil-frost

There is a way, but you don’t end up with an amplifier that you can connect to an ordinary rig. The trick is to express the signal as phase and amplitude . Consider: with an ordinary non-linear amplifier (such as typical for FM use, for example) you can manipulate phase (and thus, also frequency), but the amplitude is fixed by the amplifier’s supply voltage. What if you vary the supply voltage? You then have a way to also manipulate amplitude. If you can manipulate phase and amplitude, then you can express anything that can be expressed in I/Q representation — the only difference is that you are doing it in polar coordinates instead of Cartesian coordinates. Now you have the problem of making an efficient “amplifier”, the output of which is the power supply for the class C amplifier. However, since the amplitude variations are much slower in this polar domain (for PSK31, only 31.25 Hz), this is a substantially easier problem. A switch-mode power supply can do the task. This seems pretty simple, so you might wonder why everyone doesn’t use amplifiers like this. The trouble lies in implementation details . However, if you are designing for the specific case of PSK31, then you can take specific knowledge of the modulation into account for your design. Also, PSK31 is such a simple and slow scheme, the challenges are much less than they would be if we were trying to make an amplifier for a cellular phone or Wi-Fi radio. Tags: digital (Prev Q), amplifier (Prev Q) (Next Q)

Power Questions Q: How do I power my radio in a vehicle mobile install? Tags: power (Prev Q) (Next Q), mobile (Prev Q) (Next Q) I want to install a 30W mobile UHF radio in my car. I already have an antenna and mounting bracket - but how do I get power to this radio? It has an SAE bullet connector on the back - do I just need a cigarette lighter adapter, or do I have to wire it in somewhere else? Do I need a fuse? Tags: power (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: dan-kd2ee Answer

by dan-kd2ee

While many transceivers and scanners can be powered by a cigarette lighter adapter, you typically want to run at most one transceiver in this way, and should make absolutely certain that you know where that lighter is getting powered from. Most car fuseboxes are relatively easy to access, and most owners manuals will tell you what fuse is associated with each cigarette lighter - if the fuse is anything less than 10 Amps, do not use it. Absolutely do not change the fuse to something higher. Some possible concerns include the fact that your radio will likely start drawing it’s full current only occasionally, but suddenly. Intermittent current draws like that are less likely to pop fuses than constant draws, even if the current is greater than the fuse’s rating. On the other hand, you may experience voltage drops when you key up due to the resistance in the wire between your radio and battery. In the worst case, your cigarette lighter may be wired for “chassis ground return”, where that 10 amp current is not being returned through a copper ground wire, but through the car’s steel chassis. This is OK for stuff like an AM/FM radio or the cabin lighting, but that same resistance equates to a higher voltage drop with your 10 amp radio, which can distort your output signal or even cause devices to sense an “undervolt” condition and shut down. And as an added bonus, guess what else is connected to your vehicle chassis? Yep, that’s right, your antenna ground! So now you may have three different actual grounds all connected together, but at different voltages because of the resistance in the chassis: Your power supply ground at the radio, your RF ground at the antenna, and the actual negative post of the battery. This situation can mess with the bias of your final RF amplifier causing signal distortion or overheating. The best way, and the ways the pros do it, is to run a separate pair of wires from the battery to the radio. These wires must be rated for the maximum current draw of the radio (and then some, since every ham initially plans to install one radio and then winds up with

5) and both positive and negative leads must be fused at the battery. If they aren’t, and come into contact with anything, you may short your car battery causing a fire. There’s another bonus of connecting directly to the battery - some cars shut off the cigarette lighter when the car is off, but if you connect straight to the battery, you have control over how the power is controlled. There are low voltage disconnects intended for this purpose which will detect when the car is turned off and shut off the radio a fixed amount of time later, but which can be overriden to allow you to operate the radio without turning on the car if needed. Answer

by adam-davis

A 30W UHF radio should consume less than 10A, which is the limit of most cigarette lighter outlets. You can try it out, and if it blows the fuse, replace the fuse and choose a different option for powering it. Since the outlet is fused, you don’t need to add an additional fuse inline with the radio power. Beyond that, I suggest you check your user manual and the manufacturer’s suggestions for installation. It’ll vary based on the vehicle and whether you want it to work with the engine off or not. You may be able to find an automotive radio/alarm installer that could perform the install for you as well, if not talk to your mechanic. Tags: power (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: How can I prevent my mobile radio from draining my vehicle’s battery? Tags: power (Prev Q) (Next Q), mobile (Prev Q) (Next Q) I’m a very absentminded ham. I have a radio mounted in my car, wired directly to the vehicle battery. Fuses and high-gauge wire and all that good stuff. But, if I accidentally leave it on, my battery will be dead by the next morning! I don’t know anything about ignition sense wires or anything like that. What’s an easy way to prevent draining down my battery? Tags: power (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: dan-kd2ee Answer

by adam-davis

If you search for “automatic power off car ham ” you’ll find a number of solutions which don’t require additional wiring. When the engine is running the voltage supply is higher than when the engine is off, so these work by sensing when the voltage is high enough, and turning the radio on. Answer

by bill–k5wl

Some radios, such as the Yaesu FT-857D, have a feature in the menu that allows you to set the unit to automatically power off after a user-chosen period of time. Search the

documentation of your radio for such an option. Answer

by kd7kuj

Research automotive relays; They are essentially electronic switches that turn on when a current is present. In my vehicle, I have a large gauge wire and fuse running from the battery to high power pin on a relay under my seat; A small gauge wire runs from the back side of the cigerette lighter (which is only powered when the car is on) to the relay coil feed (trigger) pin, and another large gauge wire running to a fuse box that all my radio equipment connects to. It effectively creates the ignition sense you seek, and you will learn about the science as you go along! I have cited this resource in the past; It’s thorough, and it applies well to this task: Tags: power (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: Power dissipation in transmission lines? Tags: power (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) I was wondering, does the impedance of a transmission line have any effect on the power it dissipates? I’m familiar with the fact that an impedance equal to the load will provide maximum power transfer (and dissipate just as much power as the load) but guess that’s of no bearing when talking about transmission lines? If a line is rated as 50 Ohm, does it have any impact on power dissipation? Tags: power (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) User: s3c Answer

by dan-kd2ee

No. The cause of power loss in a feed line is not due to the characteristic impedance, it actually varies among transmission lines of the same impedance. Otherwise all 50 ohm coax would be the same - but there are many different types and qualities of cable. The actual loss is measured not in ohms but in decibels per foot, and varies with both the type of cable and the frequency in use (with higher frequencies having greater loss, due to skin effect). If you need to get the loss of a particular cable, or compare two cables, you should get a chart or table from the manufacturer. This table lists some common types of coax at a variety of frequencies. The 50 ohm value being described is not the impedance of a circuit element, which is a word for the complex form of resistance. It has a 50 ohm characteristic impedance. It’s still the ratio of the voltage to the current, but in this case of a wave travelling down the core and back along the shield. It’s a property of how the line behaves in response to a wave travelling through it, and it’s important because if it doesn’t match at any given connection, since current coming in must equal current coming out and that means the two

sides would have different voltages, part of the wave is reflected to allow everything to even out. However even though it’s measured in ohms, it is not related to resistive loss. Tags: power (Prev Q) (Next Q), feed-line (Prev Q) (Next Q)

Q: What is the point of a SWR/power meter where the needles cross over each other? Tags: power (Prev Q) (Next Q), impedance (Prev Q) (Next Q) There are SWR/power meters with two separate gauges, and others that have them mounted so the gauge needles cross over each other. Aside from looking cool, does the cross-over point of the two meters provide specific or useful information? Tags: power (Prev Q) (Next Q), impedance (Prev Q) (Next Q) User: adam-davis Answer

by michael-kjörling

A properly calibrated cross-needle power meter such as e.g. the MFJ-842 actually tells you something more than just the forward and reflected power, which as you point out can just as easily be indicated by two separate instruments. The intersection of the needles gives you a pretty good indication of the actual standing wave ratio or SWR because the SWR is directly related to the relationship between the forward and reflected power. So, there’s more utility to this than simply “saving space” or “looking cool”. Of course, you could have a third meter showing the resultant SWR based on forward and reflected power indicated on two separate instruments, but why bother when you can put all the information into one and at the same time reduce the risk of measurement inconsistencies? Tags: power (Prev Q) (Next Q), impedance (Prev Q) (Next Q)

Q: What makes cellphone transmissions so energy cheap? Tags: power (Prev Q) (Next Q) The modern cellphone can carry on a full duplex conversation for a time period measured in hours on a battery half the size of my handheld transceiver. My transceiver can barely receive for that length of time on its pack, nevermind transmit, and that’s if I have a huge antenna much more unwieldy than the antennas included in modern phones.. One issue is that the cellphone in urban areas only needs to transmit a few miles, and the receiver can be significant more energy expensive to pick out weak signals. In terms of our hobby, Repeaters are equivalent - allowing a smaller, more energy efficient handheld appear to be a big transmitter nearby - but the handheld is still an energy hog, and still limited to a small area around the repeater. Besides, the average cellular phone will still work for hours of talk time even when the nearest cell site is 10 miles away. Given that the technology exists, what is it that’s preventing our amateur radios from achieving such good energy efficiency while still reaching a dozen miles for voice

communications? Tags: power (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

Remember that carriers are selling bandwidth, that’s it. Actually, they are overselling it, exactly like cable modems (but that’s another story). If everyone in the coverage area of a cell tower tried to make a call at once, most of them would be unhappy. The carriers paid a boat load of money for their chunk of spectrum and their overriding goal is to maximize their use of their chunk. Since there is (in theory) competition, there is a focus on quality of service since all the plans seem strangely similar in price. Towers are expensive, but as the others have mentioned, phones only have to transmit a few km at most to hit a tower and often less than 1 km in urban areas. Cell phones use a heavily optimized spread spectrum digital mode that is focused on short haul weak signal work. Towers have a limit of 100W (omnidirectional) or 500W directional, however, in practice towers typically transmit in the range of 25-60 watts. In most countries cell phones are limited to 2W PEP, however most modern cell phones have a peak power of about 300mW and are typically transmitting in the 100mW range. In order to limit interference with adjacent sites, cell towers actively manage the transmit power both in the tower and on phones throughout a call, even between words. In this case, what’s good for the carrier is good for the consumer since their drive to minimize power use means the phone’s battery lasts that much longer. Contrast this with HTs First batteries – Economy of scale has let cell phone manufacturers use custom LiPo batteries for years where these are only now becoming standard on HTs. Lots of the HTs out there have NiMH or even NiCd batteries still; a lower energy density. Power – If a cell phone were to transmit 5W PEP FM, it would run dead just as fast as an HT with the same size battery. The energy efficiency is in the mode used and the fact that the required range is very low. Role – Cell phones are designed to work only where people typically go: on the roads, shopping areas, cities and the infrastructure is sited to handle that. However, people that use HT’s typically spend a good part of their time in places people don’t go as much: parks, woods, mountains. So you’d need more range even if you were using the same mode. As Phil mentioned, we’ll see advanced features in add on modes first like D-STAR (Icom) and C4FM FDMA (Yaesu). Of course, these guys are looking to sell radios, to there’s no incentive (yet) to agree on a protocol. Initially this will just allow add on services. It would take something major before people start replacing repeaters with ones that actively manage power. Heck, it’s all some clubs can do to keep a basic 2m repeater up 24/7/365 on volunteer labor.


by pearsonartphoto

There are far more cell phone towers than repeaters. Imagine if you lived only 2 miles from a repeater. You’d probably hit it with only 1W all the time, and have no problems getting a full quieting signal. Cell phone towers are commonly even closer than that. As far as receive only, you should be able to receive for a long time on a simple battery. Perhaps there’s some amplification of weak signals going on, but I’m not sure. Think of a portable FM radio, the batteries in that should last for quite a while, especially if using headphones and low volume, which is probably comparable to a cell phone near someone’s ear. Also, cell phones have a protocol designed specifically to use low power, ie, digital modes. There is a strong signal sent to get their attention, then they automatically drop in power to the lowest transmission power required to make the connection. Bottom line is, for Amateurs to have similar service levels, there would have to be some sort of a centralization, which would complicate the system. It could be attempted, and I think has been, for SHF signals, but overall, Amateur Radio is decentralized. However, some gains could definitely be made by moving to digital modes, and some sort of feedback to the device on the signal quality so the power transmission could be appropriately managed. Tags: power (Prev Q) (Next Q)

Q: Does the Crystal Radio really work? Tags: power (Prev Q) (Next Q) I am in 12th std, the reason why I am mentioning this is that we are given a PROJECT to do in Physics subject. And then one day I searched the internet and found this amazing thing called ‘Crystal Radio’. And when I showed it to my group(since it is a group project), their faces were like WTF??? Because the crystal radio works only on the energy of radio waves and no external power source!!! And my friends then started to ask me that how can this be possible… Then we went to our Physics teacher and he said that he made a crystal radio when he was in 11th and it didn’t worked for him since the energy produced by the receiver is very small… I didn’t knew what to answer to my friends then… So my short and simple question is that “Does the Crystal Radio really works??” And if yes then can you please provide the link to where can I find the working mechanism of a crystal radio… Thank You!! Tags: power (Prev Q) (Next Q) User: radiantshaw Answer

by paul

Yes, crystal radios convert radio signals to audio without any additional power. But it is true that there is not much energy in a radio signal at any significant distance from

the station, so a few tricks are involved to produce audio from that weak signal without any additional electricity: 1. The earphones are special models that are high impedance and require very little current to operate. Modern earbuds like you use with a mp3 player or cellphone have a low impedance and will not work. 2. These earphones are connected as the load to a high Q resonant circuit, which collects and concentrates energy at the desired radio frequency. 3. AM radio in particular can be decoded to audio with a diode or crystal. Other more modern modulation types (FM, Digital Audio) can not be decoded in this way. Getting a crystal radio to work depends upon having some strong local stations, a good antenna AND ground, and not having a good ground will keep it from working. If you have copper plumbing, attaching to the cold water service can be a good ground if the water service arrives from the ground without any plastic PVC pipes. Here are some links which may give you a fuller understanding: Tags: power (Prev Q) (Next Q)

Q: decibels as ratio and dBm as absolute values Tags: power (Prev Q) I am just trying to understand the nitty gritty of using decibels and absolute measurements in dBm. I see them referred to routinely in RF, and using reference sheets I can understand enough to make sense of gains and losses, but I would like instead to acquire a much better understanding for myself, being able to convert and calculate freely (without the need for reference sheets) between any power or dB value. I think I understand that dB is merely a ratio of measurement. But if, for example, a component under test had 20W at its input and 15W at its output and there is an overall loss of 5W, how would that be worked out and expressed in a ratio of dB? Trying to work it out I did: 20W (in) = 10log10(20W/1W) = 13dB(W) 15W (out) = 10log10(15W/1W) = 11.76dB(W) so, component power loss = 13dB(W) – 11.76dB(W) = 1.24dB(W)

However, I can see that I am merely subtracting absolute measurements still and not determining the dB ratio of power transfer efficiency or loss. If so, then what would be the equivalent dB ratio for this example? In addition, I am able to convert 13dB(W) back to watts with: 10 to the power of (13/10) or 10^1.3 = 19.95W

and so too for 11.76dB(W): 10^1.176 = 14.997W

but for 1.24dB(W): 10^0.124 = 1.33W

which does not appear correct, as I expected instead a value of ~ 5W, for which 1.24dB(W) represents between 13dB(W) and 11.76dB(W), so I unsure where I am going wrong. If someone could let me now I would sure appreciate the insight. Finally, what would it mean to say a receiver has a receive level of -45dBm? Is it right to conclude that such a receiver is capable of extracting information from signals received at -45dBm less power than what they (signals) were originally transmitted at? Or actually it just occurred to me that since 45dBm is an absolute value that it perhaps means that the receiver could receive signals as low as -45dBm or: 10^(-45/10) = 0.0000316mW

and still be able to extract the information transmitted so long as the S/N ratio is adequate? Which if that was the case then, if one transmits a signal with 20W or 43dBm of power, then the signal could be attenuated by up to 88dBm: 43dBm - -45dBm = 88dBm

and still be detected adequately enough by the receiver in question so that the original information sent is received? I hope I have explained my questions well enough to be easily understood. Tags: power (Prev Q) User: nanker Answer

by kevin-reid-ag6yo

Trying to work it out I did: 20W (in) = 10log10(20W/1W) = 13dB(W) 15W (out) = 10log10(15W/1W) = 11.76dB(W) so, component power loss = 13dB(W) – 11.76dB(W) = 1.24dB(W)

Your error is merely in the units, not in the calculation. Taking the difference of two dBW (or any two absolute dB values using the same reference level) gets you dB. If you want to think of this algebraically, you could use the definition x dBW ≡ x dB + (1 dBW) where (1 dBW) can be treated as a funny-named constant we don’t need to assign any numerical value to, much like any other unit symbol — except that we’re adding, not multiplying, it, because logarithms transform multiplications to additions (basic property: log(a ⋅ b) = log a + log b ). If we transform the above to non-logarithmic form, we get the trivial and obvious equation y W = y ⋅ (1 W)

Using the above definition for dBW, your calculation becomes: 13 dBW − 11.76 dBW = (13 dB + (1 dBW) − (11.76 dB + (1 dBW)) = 13 dB − 11.76 dB + (1 dBW) − (1 dBW) = 13 dB − 11.76 dB = 1.24 dB

(change notation) (reorder terms) (x − x = 0) (compute)

However, I can see that I am merely subtracting absolute measurements still and not determining the dB ratio of power transfer efficiency or loss. If so, then what would be the equivalent dB ratio for this example? The result of the subtraction is a ratio expressed in dB; you’ve just mislabeled it as being absolute. In addition, I am able to convert 13dB(W) back to watts … but for 1.24dB(W): 10^0.124 = 1.33W

which does not appear correct, as I expected instead a value of ~ 5W The 1.24 value is dB, not dBW, so treating it as an absolute value does not get you the answer relative to the original power level you measured. (However, there is a meaning to the figure 1.33 W: it’s the amount of power in that would be required to get 1 W of power out. You can check this against simply computing ratios with no logarithms.) Remember, logarithms are simply a computational convenience. If you have a calculation starting in watts and ending in watts, then you can do the intermediate work in dBW and dB (adding and subtracting) or in power and ratios-of-power (multiplying and dividing) and get the same answer. If you don’t get the same answer, you made an error in setting up the formulas. Finally, what would it mean to say a receiver has a receive level of -45dBm? … Or actually it just occurred to me that since 45dBm is an absolute value that it perhaps means that the receiver could receive signals as low as -45dBm … then, if one transmits a signal with 20W or 43dBm of power, then the signal could be attenuated by up to 88dBm: Yes, you have this right, except that it’s “attenuated by up to 88 dB”, not dBm. Answer

by phil-frost

Trying to work it out I did: 20W (in) = 10log10(20W/1W) = 13dB(W) 15W (out) = 10log10(15W/1W) = 11.76dB(W) so, component power loss = 13dB(W) – 11.76dB(W) = 1.24dB(W)

Here’s your problem: the answer is 1.24 dB, not 1.24 dB(W). Why? Subtraction of logarithms corresponds to division. You end up with watts in the

numerator and denominator which cancel, leaving you with a unitless ratio. Formally: a log(a) − log(b) = log ( ) b When you do 13 dB(W) − 11.76 dB(W) , you are actually doing: 13

(10 ) W 10






19.95 = 1.33 14.10

We can convert 1.33 to decibels: 10 ⋅ log(1.33) = 1.24 dB This also raises a point of common practice: since you are calculating a loss, it’s conventional to arrange the calculation so that the result expressed in decibels is negative. A negative number in decibels corresponds to a fraction less than 1. Example: 11.76 dB(W) − 13 dB(W) = −1.24 dB More generally: power out − power in = loss or gain in decibels Which, if you think about the identity above, is equivalent to power out = loss or gain as a ratio power in This makes the ratio not 1.33 as calculated above, but 1/1.33 or 0.752. This allows us to calculate losses in watts by multiplication. If we were to put 100W into this system, for example… 100 W ⋅ 0.752 = 75.2 W …we’d get 75.2W out. Tags: power (Prev Q)

Ht Questions Q: What’s a cost-effective way to boost the range of my cheap 2m/70cm handheld? Tags: ht (Prev Q) (Next Q), uhf (Prev Q) (Next Q) I’m a very casual/beginner level ham and as such have mostly avoided committing too much in the way of financial resources - I have a UV-5R for a personal radio, anything else I do I’ve used others’ radios. I don’t mind the 5R’s interface; I’m familiar enough with it now that it doesn’t really bother me. That said, it’d be nice to give it a little boost without spending a bunch of money and/or buying a new radio. I typically operate at home, so mobility isn’t required (though being able to pack it up to have along when traveling wouldn’t hurt, either). What kinds of low-cost options are there that could help improve its range (and/or SNR)? Tags: ht (Prev Q) (Next Q), uhf (Prev Q) (Next Q) User: amber Answer

by dinesh-cyanam

A homemade “rat-tail” ground plane costs 35 cents each to make. A crimp on eyelet to fit your antenna’s connector, a string of speaker wire about 19-20 inches long and a little heat shrink tubing to dress it up and done. Soldering the the wire to the connector instead of crimping it will be a better option. Go here for some details about the “Rat-Tail” ground plane: Answer

by rob-t.

There have been a number of good answers already, though I think there are a few additional points worth sharing. Answers would also be more relevant if we knew what situation(s) you were coming up short range wise. For portable use (out in the field): 1. The stock Baofeng rubber duck antenna has been shown to be a poor performer. All of the stock rubber duck antennas tend to be a compromise and not perform very well, but the stock, stiff, short baofeng antenna seems to perform worse than others. 2. An antenna that is physically close to the right wave length (1/4 wave, 1/2 wave, or 5/8th wave) on the frequency you want to operate on will perform better (have less signal loss) than a shorter antenna. While it’s inconvenient to carry around, a 14-15

inch “gain” antenna can help in many cases where a 4-8 inch stock duck can’t be heard. 3. The standard rubber duck antennas are 1/4 wave, which are half of a 1/2 wave dipole, oriented vertically. Your body is making up the other half, the ground plane. The rat tail suggestions are good ones, which are providing a better ground plane to complete the other half of the antenna. 4. Get the radio off your belt! If you are using the headset with the radio attached to your belt, your body is absorbing much of the signal. Bring the radio up to your mouth when transmitting. 5. Make sure your battery is fully charged. Your radio is only putting out the rated power when it is getting the design voltage. The lower the voltage from your battery, the less your power output (in watts) will be. Several graphs of power vs. battery voltage have been published for the Baofeng and the similar Wouxun online and in the Yahoo groups. For use in a car: 1. Get your antenna OUTSIDE of the car. The body of the car will absorb much of the signal. A magnetic mount antenna can be a good non-permanent solution. Make sure you’ve got enough metal in the roof and that the antenna is as close to the center of the roof as you can. 2. Power the radio from the car to ensure you are getting the full output power your radio is capable of. Use a 12 volt battery eliminator. For use indoors: 1. Get your antenna outside, especially if you are using 2 meters. The shorter 70cm waves have a much easier time getting through window openings than the longer 2 meter waves. There are many simple choices that don’t involve trying to put a large antenna on a roof. A magnetic mount antenna for a car placed on a window air conditioner works well. 2. Use 70 cm where possible instead of 2 meters if it’s appropriate for your area. 3. Use a power supply to make sure you a getting full output power. General: 1. Height and Line of Sight are your friend. 2. 2 meters and 70 cm perform differently and have different advantages depending upon the surrounding terrain. It’s good to know which one to use. 70cm is better in urban areas. 2 meters will give you longer distance propagation in open areas. Important General Tip: The pin inside the SMA antenna connector will eventually break! The connector is rated by design for approximately 500 connection cycles. If you use one antenna and rarely disconnect it you’ll be fine. If you change antennas frequently, consider using a low profile BNC adapter where the base sits on top of the radio and isn’t completely dependent on the SMA jack for all of its mechanical strength.


by paul

If you don’t need mobility, purchase an inexpensive directional 4 element Yagi antenna for 2m and operate it in vertical polarization, that is with the prongs of the yagi pointing up and down. You can sometimes find these small Yagi antennas used for ~$20-30. But note this will only help you for 2m, and should not be used on 70cm. For 70cm you can get a 70cm antenna, or perhaps find an antenna designed for both bands. This will add cost, however. One warning about external antennas: convert from big coax down to smaller coax and a BNC or SMA plug near the HT instead of using the big coax with an adapter; a PL259 to BNC/SMA adapter may tear the bnc/sma plug from the wiring or circuit board of an HT. Tags: ht (Prev Q) (Next Q), uhf (Prev Q) (Next Q)

Q: Mobile phone models that contain 2 way radio functionality Tags: ht (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) Are there any mobile phone models there that contain 2 way radio functionality? Tags: ht (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q) User: s-k’ Answer

by kawfey

Yes indeed! Legally, you can only use these if you’re a part 90 operator, or a ham, just like the Baofeng/Wouxun/Chinese radios, and the cellular side works as an unlocked phone. Answer

by wprecht–ab3ry

The smarmy answer is of course, that cell phones are two way radios on either the 800Mhz band (Sprint & US Cellular) or the 1900MHz band (all the others). Not what you meant, I know. The old Nextel phones with their “push-to-talk” feature were two-way radios using the old 50 MHz taxi-dispatcher band. Later versions of this technology used 900MHz. I found a couple of references to cell phones that incorporate what looks like FRS service in the 446 MHz band with a claimed range of 5km ( is an example). Tags: ht (Prev Q) (Next Q), software-defined-radio (Prev Q) (Next Q)

Q: What’s wrong with 220MHz? Tags: ht (Prev Q) (Next Q), mobile (Prev Q) (Next Q) It seems like 220MHz is the bastard step-child of the amateur world. Every HT is either 2m or 2m/70cm. Some companies offer tri-banders, but they almost always add 6m (?!), not 220MHz. The only way to get this band easily is the Chinese radios. I have a BAOFENG UV-5RC which is 2m/220MHz, and I have seen for sale single band 220 MHz mobile unit from TYT. In an otherwise competitive market, it seems odd to me that none of the major makers have 220 in their lineup. Why? Tags: ht (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: wprecht–ab3ry Answer

by michael-kjörling

While for an authoritative answer to this I believe you’d have to ask the manufacturers directly (unless we happen to have someone here on the site who works for one of them), there is a pretty big plausible reason why so few multiband radios include 220 MHz capability. The band is allocated to amateur radio mostly in the United States and Canada. (Source: Wikipedia .) Outside of ITU Region 2, the only country listed as having an allocation there is Somalia. On the other hand, with minor differences in frequency ranges for which it is trivial to implement restrictions in software only, two meters and 70 cm are both allocated to amateur radio practically worldwide. Since 220 MHz also is not harmonically related to the band pair two meters and 70 cm, adding it to an existing design would probably require a fairly significant outlay in new electronics, filters etc. You would, at the very least, need to fix up the receiver so it performs well on the band, add the ability to tune the VFO to the band (assuming you don’t already have a wide coverage VFO) and add a proper band pass filter to filter the transmitted signal. Other steps might be needed as well depending on the particular transceiver design. There is also the related problem that a 2m/70cm antenna is not resonant at 1.25 meters, which increases the risk of damage due to mistakenly transmitting into an unmatched load. It would seem that manufacturers don’t consider the demand for 220 MHz capability to outweigh the cost of such design changes for a relatively limited market. The conclusion we can draw from this line of reasoning is that the reason why none of the major manufacturers include a multiband HT with 220 MHz capability in their lineup is precisely because it is a competitive market. Answer

by adam-davis

220MHz has a long and storied history

which leads to the lack of available equipment,

and thus low adoption rates in the Amateur Radio community. The short version is that two things contributed to its lack of usage: Few commercial bands are near enough that existing equipment can be simply modified to serve this band. There are numerous commercial bands near 2M and 70CM, thus many, many commercial products can be modified, or simply used without modification, to serve those bands. However there are few products readymade that can easily be modified to run in the 220MHz amateur radio allocation, and it’s been this way for decades. The band has been, at various times, allocated and reallocated, divided, and placed on secondary use for some portions over the last several decades. Some are hesitant to invest in a band with such a variable history, which suggests that it may not be available in the long term. We do have a handful of products now, and enterprising amateurs are setting up repeaters and encouraging use so that, unlike in the 90’s, a commercial service can’t easily show that it’s not well used by the amateur community. But due to its history, and the lack of nearby commercial bands and equipment, it simply isn’t as popular as 2M and 70CM. Tags: ht (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Q: How do I troubleshoot a Baofeng UV-5R that won’t receive? Tags: ht (Prev Q) (Next Q) I have a couple of Baofeng UV-5R radios. I have a profile in Chirp that works great on one of them, and I foolishly pushed that profile straight over to a UV-5R without checking firmware versions. Chirp crashed, and now the radio won’t receive. I’ve tried resetting it to factory settings, downloading the factory settings in chirp, and then importing a csv of my channel configs, but it still doesn’t make noise when I transmit. I have noticed that it does receive when I hold the MONI button, but there’s no indication of reception if I don’t hold that button down. It appears to behave like the squelch setting is too high, but it’s currently set to 3. For what it’s worth, the radio still transmits just fine. Tags: ht (Prev Q) (Next Q) User: benson Answer

by benson

I did a bit more reading, and it seems that the new version of the firmware meant I needed to use a different chirp profile. The solution that worked for me was to find a factory image from a radio with the firmware version I have (which Chirp reported), then import my channels via csv, and clone that resulting image onto the radio.

Tags: ht (Prev Q) (Next Q)

Q: Is using an HT and walking considered mobile? Tags: ht (Prev Q), contest (Prev Q) (Next Q), mobile (Prev Q) (Next Q) I’ve seen many contests define mobile as something like being able to legally move and broadcast. Well, using an HT while walking I can legally move. Does this count as mobile contacts for a contest? Tags: ht (Prev Q), contest (Prev Q) (Next Q), mobile (Prev Q) (Next Q) User: pearsonartphoto Answer

by kevin-reid-ag6yo

Insofar as there is an agreed-upon definition of the term “mobile” (and “portable”, which is closely related/confusable and so I’m covering it here), this is how I have most frequently seen the terms used when people are being precise about it: Portable: A station set up in a temporary location. If you’ve parked a radio on a picnic table and strung a wire antenna to a tree, you’re operating portable. In some contexts there may be the additional implication of being a significant distance from your home location. Mobile: A station which is capable of being operated while in motion. The most common type of “mobile” is a station installed in a car/truck. For other means of transportation, you usually hear it qualified as “pedestrian mobile”, “bicycle mobile”, “maritime mobile”, etc. I’ve never seen anyone say that pedestrian mobile isn’t a kind of mobile. So, to the first question you asked, Is using an HT and walking considered mobile, I say “yes”. (And practically, however you’re labeled, you’ve taken on the limitations of a mobile station — small antenna, no earth ground, battery power, etc.) But in any specific actual contest — if the rules aren’t clear, ask for clarification. It’s the opinion of the contest organizers that actually matters. Tags: ht (Prev Q), contest (Prev Q) (Next Q), mobile (Prev Q) (Next Q)

Software Defined Radio Questions Q: What happens when I and Q are switched? Tags: software-defined-radio (Prev Q) (Next Q), direct-conversion (Next Q) In

it’s shown that one can use −−−−− −2 2 r = √ I +Q

to decode AM signals from a direct conversion receiver. It appears that, in this particular case, I and Q are interchangeable, thus the SDR doesn’t care which is which. Is this true, and for straight AM they can be switched without issue? Are there other modes, such as SSB and CW, where switching I and Q wouldn’t matter? If I’m operating an SDR, what clues can I look for that would indicate a swapped I and Q? Tags: software-defined-radio (Prev Q) (Next Q), direct-conversion (Next Q) User: adam-davis Answer

by phil-frost

Swapping I and Q reverses all the frequencies. For example, a signal 5 kHz above the mixer’s LO will appear at -5 kHz, instead of 5kHz. CW and AM are symmetrical in the frequency domain, so it doesn’t matter for the purposes of demodulation, though your software is likely to display the wrong frequency. SSB is not: reversing I and Q will make USB look like LSB, and LSB look like USB. If you have a waterfall with lower frequencies on the left, then tuning to a higher frequency should shift everything to the left. If it goes to the right instead, you know I and Q are reversed. Tags: software-defined-radio (Prev Q) (Next Q), direct-conversion (Next Q)

Q: SDR: Quadrature demodulation vs direct RF sampling Tags: software-defined-radio (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q), directconversion (Prev Q) (Next Q) I see that many SDRs use a quadrature demodulator and sample I and Q signals. But is it possible to downconvert the RF signal instead, sample it with only one ADC, and get the same capabilities of digital postprocessing?

So if we want to observe 100-150 MHz bandwidth: we pass it through a 100-150 MHz bandpass filter, downconvert it to DC-50 MHz, and sample it with a 100 MHz ADC. Will it work? And if it will - why is IQ so widely used? Tags: software-defined-radio (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q), directconversion (Prev Q) (Next Q) User: barsmonster Answer

by phil-frost

Sure, it would work. In fact, if you’ve ever used something implementing some digital mode that interfaces with an SSB tranciever, this is exactly what is happening. Many TNCs and most PSK-31 software is an example of this. The reason I/Q is more frequently used is that it’s simpler. If you want an SDR with 50 MHz bandwidth, you can do that with a single 100 MHz ADC as you describe, or two 50 MHz ADCs and I/Q sampling. Either way, it’s 100 million samples per second, so the ADC complexity is essentially the same. The difference is in the mixing. An ordinary mixer works by multiplying two signals. This creates two sidebands, the sum and the difference of the frequency components of the two mixer inputs. One of these sidebands must then be filtered out. Good filters are hard to realize, digital or analog. However, if you have the signal in I/Q form, the signal can be multiplied by a complex exponential . This doesn’t create sidebands: it directly shifts all the frequencies up or down by some frequency. This is more directly what we usually want to accomplish with a mixer. There are additional benefits: the discrete Fourier transform (DFT), used in a great many DSP techniques, works on complex numbers. When we don’t have I/Q data to provide it, then we must arbitrarily set Q to something (usually 0). As a result, half the result of the DFT (all the negative frequencies) are just a mirror of the positive frequencies, so they are discarded. This is computationally inefficient. Answer

by alan-campbell

One of the earlier SDR models, the HPSDR, had/has a single receive board: the “Mercury”. It used a single high speed ADC. Details are here. Once the RF if sampled and fed into an FPGA, it typically gets split into I and Q streams anyway. If you have a 120Msps ADC, for example, you could mix with a 30MHz SINE signal (0, 1, 0, -1, repeat) and a 30MHz COSINE signal (1, 0, -1, 0, repeat). Benefits? Well for starters, you’ve halved the number of ADC’s and associated amps, physical filters, etc. You still have them - but now they need to be implemented In Code in the FPGA. Seperate I and Q channels also tend to have distortion problems around DC. Drawbacks? You have to wite more code. Some of that code (the complex exponential) can be quite hard to do well. Edit: Another expense-related problem: your single ADC now has to be twice as fast. This can significantly impact ADC Cost, and even the circuit

design. As for your idea of looking at 100 - 150MHz: this is where oversampling comes in. If you sample a 60MHz signal with a 100MHz ADC, the Nyquist effect makes it “look like” a 40MHz signal, ie. reflected around the half-sample rate. A 90MHz signal will “look like” a 10 MHz signal. What would a 101 MHz signal look like…? It would look like a 1 MHz signal. This is oversampling. Looking at a bandwidth of (up to) half the sample rate, while technically possible, is pushing things a bit. In practice, for the conditions you specified, I’d use ADC’s rated at 160Msps (or higher), and expect data between 60 - 10MHz. Such ADC’s don’t come cheap, so I’d probably consider a single ADC version to start with. Also note how the frequency band got “reversed” by using the Nyquist oversampling. This can impact decoding analog TV (color burst in wrong location), SSB (LSB becomes USB), and commercial FM (stereo information in secondary signal). Tags: software-defined-radio (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q), directconversion (Prev Q) (Next Q)

Q: Why do SDR control apps have two frequency settings? Tags: software-defined-radio (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q)

Why do many SDR control apps have two frequency settings, even when the app is designed or set up only for listening to or decoding one signal? Should the two SDR frequency controls be set differently or the same? If different, how much for which modulation schemes (CW, USB, LSB, AM, etc.), in which direction, and why? Tags: software-defined-radio (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q) User: hotpaw2 Answer

by kevin-reid-ag6yo

One controls the hardware, and the other controls the software. 1. The hardware selects some section of the entire RF spectrum (by a local oscillator and mixer), and down-converts it into a frequency an analog-to-digital converter can handle, filters it (to discard out-of-band signals), samples it, and delivers that data to the computer. This data determines what you can see in the so-called “waterfall” or “panadapter” displays. It also sets the limit for the widest-bandwidth signal you can possibly demodulate. 2. Then the software does a similar process in order to select a single signal to demodulate; it shifts it to baseband (a “0 Hz” signal which only varies according to the modulation), applies a low-pass filter, and demodulates appropriately. Both stages have their own controllable local oscillator, and those two controls are what you are seeing. Here are some reasons for there to be these two separate stages: Analog hardware is imperfect; there are various sorts of garbage you can get in the digital signal (DC offset, IQ imbalance, insufficiently filtered out-of-band signals). You can change the hardware center frequency to shift the garbage away from the signal of interest.

For example, if there is a DC offset (RTL-SDRs with E4000 tuners do) then you have garbage at the center frequency, so you would set it to be slightly different from the signal of interest so that the following digital filter removes that part. This is one of the main reasons to specifically set the two frequencies differently, if your receiver has this problem. It doesn’t matter which direction you offset, as long as the offset is enough that the bandwidth of the desired signal doesn’t overlap the unwanted signal. On the other hand, filtering is imperfect and the way this shows up in the signal from the hardware is that signals which are out of the tuned band, but strong, will be seen to “wrap around” and appear at an in-band frequency modulo the hardware bandwidth (sample rate). This is a reason to receive close to the center; the hardware filtering is at its best at that point. I highly recommend playing with changing the (hardware) center frequency slowly and watching and listening to how the displayed signals change or don’t. You will learn what to do. If you are interested in monitoring a whole band rather than a single station (e.g. a single amateur HF band) then keeping the hardware settings fixed leaves your waterfall display undisturbed to watch activity over the whole band while you are free to select which stations you are currently demodulating (listening to). Digital filters can be optimized for the particular mode in use, and, if you don’t care about power consumption, be extremely sharp (good at selecting exactly what is wanted) compared to analog filters. They can also be adjusted in bandwidth or shape to trade off filtering out nearby unwanted signals vs. better intelligibility in the absence of nearby signals. (Note that this is a reason for the two-stage architecture, but it isn’t directly a reason to have independent tuning controls as you’ve asked.) Tags: software-defined-radio (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q)

Q: Configuring an SDR for CW? Tags: software-defined-radio (Prev Q) (Next Q), cw (Prev Q) (Next Q) So I’m developing my own SDR software from scratch (I like to “own” the code). The channel between the RF-to-USB hardware and the software is 192kHz sample-rate IQ audio samples. The degrees of freedom seem to include at least 4 frequencies and a switch. The 4 frequencies are: RF filter frequency, external tuner reference oscillator frequency, software complex multiplication oscillator frequency, software bandpass filter center-frequency (also filter bandwidth). Then select from I, Q, I+Q, I-Q, or abs(I,Q) for audio output. Then resample as necessary to match the audio output API. So assume I set the 1st frequency (front-end RF filter) to the HF band of interest, the 2nd HF reference oscillator to the middle of some CW HF band. Now say I find a QSO 12.500 kHz up from the HF reference oscillator, and I’d like the resulting Morse Code audio side tone frequency to be 750 Hz.

Where do I set my software oscillator frequency for the complex multiplication and what do I want my software bandpass filter center frequency to be to hear Morse Code with the desired side tone? (Do I have 2 choices? If so, how to choose?) Which final IQ mux output do I select to feed the audio speaker? Tags: software-defined-radio (Prev Q) (Next Q), cw (Prev Q) (Next Q) User: hotpaw2 Answer

by phil-frost

Implementing a CW receiver in an SDR is pretty much like implementing a SSB receiver. You will tune the RF bits to some band of interest. Next, you will multiply the I/Q signal so that the CW signal you want to receive is at 750 Hz, if that’s your desired pitch. Next, you must filter. There are two reasons. The obvious reason: you don’t want to hear everything in the band. But also, the I/Q data contains both positive and negative frequencies. Frequency 0 corresponds to the LO frequency (plus the shift you introduced in the multiplication step above). Negative frequencies are below that, positive frequencies above. We need to, at some point, get rid of these negative frequencies, because they correspond to the LSB sidebands which we don’t want or need. After you’ve filtered, all the negative frequencies will be attenuated by the filter’s stopband. Now we can take I, just Q, or I+Q, or I-Q (the only difference between each is the phase), and what you will hear is all the positive frequencies, plus all the negative frequencies. However, since we filtered the negative frequencies away, we in effect hear just the positive frequencies. The only difference between this and a USB receiver is the filter width. If you want to make it a LSB receiver, all you need to do is move the filter passband into the negative frequencies. For an example, see this example in GNU Radio Companion by OZ9AEC . GNU Radio Companion can be a good source for examples because it’s programmed by graphical flowcharts. Here’s one from that article:

There are some FFT Sinks which are graphical UI elements just to visualize the data at that point. USRP Source configures his particular hardware. The Frequency Xlating FIR filter performs the multiplication step, while additionally resampling the data (the USRP has a very high sample rate). Then there’s a band pass filter, and he’s added some automatic gain. Rational Resampler resamples the data again to get it down to an audio sample rate. Complex to Real discards Q and gives you just I. The multiplier at the end is a volume control, then it goes to the speakers. Also if you look closely, the cutoff frequencies for the band pass filter are negative. As configured, this is an LSB receiver. Make those positive, and narrow, and you have a CW receiver. Answer

by user2338215

In my app “iSDR”, I approached SDR by the book, or more correctly books, using “An Introduction to Signal Processing and Fast Fourier Transform (FFT)” by Kevin J. McGee and “The Scientist and Engineer’s Guide to Digital Signal Processing” by Steven W. Smith, Ph.D. (which is available on-line for free). The old QST series of articles titled “A Software-Defined Radio for the Masses” parts 1-4 by Gerald Youngblood, AC5OG was also very helpful. Taking bits and pieces from all of the above, iSDR implements CW receive as follows. The baseband I and Q signals are fed one into each side of a complex FFT. The FFT results are then shifted to bring the desired center frequency bin (minus the CW offset) to the zero position (DC). Then a pre-calculated frequency-domain sinc (brick wall) filter is applied to the contents of the FFT. The inverse-FFT function is then applied giving back the time-domain shifted and filtered audio. Doing the filtering in the frequency domain is very efficient since most of the calculations

are performed ahead of time. So this approach even allowed the old Apple iPod touch second generation device to do a convincing (if suboptimal) job of demodulating CW, SSB, and AM signals. CW is the simplest, since CW signals simply “fall right out” of the above approach without any additional massaging of I and Q. If any of the terms used in the second paragraph sound like mathematical gobbledygook, take a look through the references in the first paragraph. The math isn’t simple, but it is extremely powerful. The few steps described in the second paragraph result in a remarkably sharp and clear receiver. iSDR provides a very usable CW filter as narrow as 100 Hz, and could easily be made narrower, except that centering it on the signal of interest becomes a challenge. Tags: software-defined-radio (Prev Q) (Next Q), cw (Prev Q) (Next Q)

Q: Why is dynamic range relevant for an SDR? Tags: software-defined-radio (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q) Sometimes I see dynamic range mentioned as a figure of merit for an SDR. For example, I know that the bits per sample used by the analog to digital converter can affect the dynamic range. Why do I care about dynamic range? What happens when I don’t have enough of it? Can I have too much of it? Does dynamic range have special significance or importance for an SDR compared to a traditional analog receiver? Tags: software-defined-radio (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q) User: phil-frost Answer

by kevin-reid-ag6yo

Signal strength and dynamic range

Generally speaking, dynamic range is the ratio between the strongest and weakest signal that can be received. In a digital signal, the dynamic range is determined by the number of bits per sample: the strongest signal is one which uses the full range of the sample values, and the weakest signal is one which uses only two adjacent values (one bit change). In a software-defined radio, the analog signal level fed into the analog-to-digital converter must be adjusted (either manually or by an AGC) to make best use of the available dynamic range: If the analog signal is too strong, then the logically corresponding digital values are not representable in the numeric range of the samples, and the ADC will substitute the maximum or minimum possible output; this is known as clipping, which from a signal processing perspective is an extreme form of nonlinearity. If you have clipping, it can be observed as the appearance of spurious signals which

are copies of actual signals in the received band at different frequencies. If the analog signal is too weak, then its presence will not manage to make even one bit of difference in the digital output. More practically, well before the one-bit point you will be losing information due to the digital sample values being too coarsegrained to accurately represent the signal. This can be thought of as a source of noise, called quantization noise.

The above image shows a sampled (50 samples) and quantized (5 bits) sine wave with different amplitudes, showing each of the above effects. Note in particular how even the relatively nice-looking sine on the left has slightly irregular points (because the sine function’s real-number values get rounded to the closest representable value): this is an example of quantization noise. Why dynamic range matters for SDRs

Given the above, it might sound like you can have an AGC that keeps the input signal at just the right level, and not need very much dynamic range. This would be true, except that in a software-defined radio of the kind we’re interested in, the signal into the ADC is much wider bandwidth than the individual signals we want to demodulate! This additional bandwidth is what allows you to get the “waterfall” or “panadapter” display characteristic of SDRs (because you’re actually digitizing a wide band of RF), but it means that the analog signal coming into our ADC contains lots of RF power which is not any one signal we want to demodulate — it includes a large amount of noise, and possibly many intentional signals, some of which may be very strong compared to the desired signal. The best analog gain setting is determined by the total RF power coming into the ADC (from the tuner and analog filter, if present). This fixes the “strong” end of the scale of possible digital signal levels, leaving the “weak” end determined by dynamic range. Therefore, the more dynamic range we have, the less quantization noise is present in narrow-band signals (which are more or less weak compared to the overall signal), allowing them to be received more clearly.

You can also improve reception with the same dynamic range by using a narrower analog filter, thus reducing the input power and allowing more gain to be applied to it without clipping — if your SDR hardware has a usefully adjustable filter. The extreme case of using a narrower filter is using one just as wide as a single signal you want to receive. The disadvantage is you don’t have any spectrum view while you’re doing that — you can only receive that one signal. Direct answers

Why do I care about dynamic range? What happens when I don’t have enough of it? Signals you want to receive disappear into the (quantization) noise floor. Can I have too much of it? As a user of a SDR, no, except as it affects the price tag. As a designer, additional sample bits: require additional computation (significant for embedded systems; probably moot if you’re using a general-purpose machine for your DSP since the samples will likely be expanded into 32-bit integers or floats for computation), require a higher-performance (expensive) ADC, and may be worthless due to noise received by the antenna (if the electromagnetic noise floor is higher than the quantization noise floor when the gain is set optimally) or noise getting into the system between the gain-control stage and the ADC (the low bits are always noise). Does dynamic range have special significance or importance for an SDR compared to a traditional analog receiver? Strictly speaking, no — it is not being software-defined that makes dynamic range matter, but the wide bandwidth. However, if by SDR you mean something with a waterfall display, then yes, it does (as described above). Tags: software-defined-radio (Prev Q) (Next Q), equipment-design (Prev Q) (Next Q)

Q: Confusion about SDR Tags: software-defined-radio (Prev Q), rtl-sdr (Prev Q) (Next Q) I’ve just written code for the RTL2832 to receive and decode ADS-B packets (very cool!). I had some confusion about what is actually happening: Is the raw data coming from the USB dongle literally samples of the ~1090 MHz wave? Or is the carrier frequency first demodulated (in that case, what actually am I receiving?)

What is the relationship between sampling rate and bandwidth? (I’ve read that it’s equal; e.g. 1 MSPS = 1 MHz, but reading about higher end SDR setups doesn’t confirm this) Isn’t the ADS-B encoding scheme particularly sensitive to phase and sampling frequency differences (like if my receiver is slightly out of calibration)? It seems that if I were sampling just a little faster or slower, that I would have received a much different signal than the one below:

Thanks! Tags: software-defined-radio (Prev Q), rtl-sdr (Prev Q) (Next Q) User: nathan-wong Answer

by kevin-reid-ag6yo

Is the raw data coming from the USB dongle literally samples of the ~1090 MHz wave? Or is the carrier frequency first demodulated (in that case, what actually am I receiving?) It’s downconverted, not demodulated, using a local oscillator, mixer, and filters. That is, the signal you obtain is the same as if the transmitter had its carrier frequency set to 0 MHz instead of 1090 MHz (ignoring for the moment the fact that negative frequencies don’t exist as propagating waves). What is the relationship between sampling rate and bandwidth? (I’ve read that it’s equal; e.g. 1 MSPS = 1 MHz, but reading about higher end SDR setups doesn’t confirm this) If your receiver has perfect antialias filtering, you can have bandwidth equal to sample rate (in a quadrature (IQ) system). In practice, your filter lets some out-of-band signals through, so whatever sample rate you pick, you get less usable bandwidth than that. To demonstrate that the filtering is not perfect, find a continuous narrowband signal (e.g. weather radio), then change the hardware frequency gradually. As the signal gets closer to the edge of the receive bandwidth, it will decrease in amplitude — but when it gets to the edge it will wrap around to the other side, weaker! This is aliasing. However, if you have a situation where you do not need to reject nearby signals or noise (that is, the signal you want to receive is stronger than everything else nearby in frequency), then you could use all of your sampling rate. But that is an unusual situation,

and not robust against interference. Isn’t the ADS-B encoding scheme particularly sensitive to phase and sampling frequency differences (like if my receiver is slightly out of calibration)? In this type of receiver, the phase and exact sample rate of your analog-to-digital converter is not the same as the phase and symbol rate of the signal you’re receiving. Instead, the software has a a control loop which looks at the incoming signal (knowing its expected properties) and adjusts to match its phase and symbol rate. The other way (phase-locking the ADC to the digital signal) is possible, but that requires additional hardware to precisely control the local oscillator, and makes the receiver hardware more specific to the characteristics of the particular modulation being received (rather than a general-purpose software-defined radio). Tags: software-defined-radio (Prev Q), rtl-sdr (Prev Q) (Next Q)

Contest Questions Q: Where on the web can I find a calendar of upcoming contests? Tags: contest (Prev Q) (Next Q) For years, I have been using SM3CER Contest Service

for HF contests.

It is always good to have a backup, so I am looking for more or better. What do you recommend? Tags: contest (Prev Q) (Next Q) User: on4aa Answer

by wprecht–ab3ry

I use the WA7BNM Contest Calendar , usually the 8 Day version is enough for me, I can’t plan much farther in advance. This one is nice with links to the rules and such so I check it regularly. There is also the ARRL Contest Calendar , it usually only has the ARRL sponsored contests though. And there is always the handy 3830 Scores site for the post contest chest-beating :). But the quickest way to get a sense of how you did. Answer

by on4aa

The PG7V HF Contest Calendar

is also a nice one.

In the meantime, I have put up a web page linking to all the calendars these answers.

mentioned in

Tags: contest (Prev Q) (Next Q)

Q: Why should I practice one month before a contest, rather than the week before? Tags: contest (Prev Q) (Next Q) I’ve seen suggestions that it’s better to practice a month prior to a contest, rather than at any other time prior to the contest. What is special about a that time frame that it would be suggested so often? Tags: contest (Prev Q) (Next Q) User: adam-davis


by adam-davis

Sunspots significantly alter propagation characteristics, and the sun revolves at a 26 to 38 day rate . Since it’s gaseous, it revolves differentially - faster at the equator and more slowly at the poles. While individual sunspots can last from days to weeks, sunspot activity on a position on the sun changes slowly over time. While you can practice at any time prior to the contest the sunspot activity will be most similar about 28 days prior to the contest, and thus propagation conditions will be most similar. 28 days works well because sunspots most frequently appear just north and south of the equator , in the bands with the most turbulence, and it fits pretty well with the 7 day week we humans tend to follow. Tags: contest (Prev Q) (Next Q)

Q: What skills will I learn from contesting? Tags: contest (Prev Q) (Next Q) I got into Amateur Radio for emergency preparation and to allow me to expand my electronics hobby. My needs are being met, but I’m wondering if I’m missing out on increasing my skills by avoiding contesting which, in and of itself, doesn’t particularly interest me. What will I learn in contesting that isn’t as easily or quickly mastered if I don’t participate in contesting? In what other ways would contesting benefit me? Tags: contest (Prev Q) (Next Q) User: adam-davis Answer

by pearsonartphoto

There are quite a few key things that can be learned by doing a contest. Here’s a few key skills. 1. Learn to copy messages exactly. 2. Improved recognition of faint signals. 3. Ability to communicate in adverse situations. If a contest isn’t an adverse situation, I don’t know what is! 4. Contesting often promotes mobile or portable communication, which is often useful in emergencies. 5. One can learn a lot about propagation. For instance, I learned during the Sweepstakes Contest that if I wanted to make a contact with Alaska, I needed to do it in the afternoon hours. 6. Learning one’s equipment. The importance of fully knowing one’s equipment cannot

be overstated! 7. Endurance. Quite frankly, talking on the radio can be quite difficult to do for long periods of time. I’ve been able to increase the amount of time that I can spend behind the radio from about an hour initially to 5-6 hours via contesting, which improves my skills. 8. Improved recognition of weak signals. I learned how to get a signal out of the noise via contests. There are a bunch of other benefits as well, such as team building, getting to know your neighbors, getting WAS and DX done, etc. But those don’t fully fit into the emergency preparedness category. Tags: contest (Prev Q) (Next Q)

Q: What prevents automation in contests? Tags: contest (Prev Q) (Next Q) It seems that using a CW skimmer with an SDR one could fully automate a contest station, and even handle multiple contacts simultaneously in the case of pile-ups. Has this been done or discussed before? What rules are common that would prevent this type of operation? What checking is done or can contests perform to find people using such methods? Tags: contest (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

Nothing. And this is a point of some controversy. In contests that allow electronic aids (like spotting networks and skimmers), the users are generally in a separate category. In some cases you go from Single Operator to Single Operator Unlimited, in other cases: Multi-Op Single transmitter. Other contests prohibit aids of any kind, including skimmers. Most state QSO parties prohibit aids under the philosophy that while they are contests, they are for “fun” and folks shouldn’t take them seriously enough to go to the effort of electronic aids. Some of the folks that do log checking swear they can detect the use of skimmers based on the logs but decline to explain how. Being a software developer, I can imagine how it could be done. Whether it is or not, I don’t know. Needless to say there are folks that claim that all these aids ruin the tradition and spirit of contests. To others, this is just the natural evolution of technology. Tags: contest (Prev Q) (Next Q)

Q: Why do some DX listen on a different frequency than they transmit on? Tags: contest (Prev Q) (Next Q), frequency (Prev Q) (Next Q) I’ve heard some DX indicate “CQ up 5” for instance, indicating that they are listening on a different frequency than they are transmitting on. What are the reasons one might want to do that? Tags: contest (Prev Q) (Next Q), frequency (Prev Q) (Next Q) User: adam-davis Answer

by wprecht–ab3ry

This is called operating “split” and it takes a certain amount of skill to work a DX operator working split and even more to operate split. The reason this is done is to help manage the pileup. If too many stations are calling and the pileup becomes unmanageable it takes longer and longer to complete an exchange. This is less fun for everyone. By working split, the DX operator keeps his transmit frequency clear so that the callers will hear him well making the exchange go more smoothly. He also has the opportunity to spread out the calling stations on several frequencies near his transmit frequency. For instance he starts out simplex, then gets spotted and the rush begins. So he calls “Up 5” meaning call him on this frequency + 5KHz. After a while he might announce “Up 10” and realistically at this point callers are spread from +3KHz to +12KHz or so in their eagerness to get through. The DX station will go through the calling stations in some order (usually). Perhaps starting at the top of the window and calling a station every 1KHz or every other KHz, or some other system. The key to navigating these waters is to LISTEN for a while and figure out how it’s being managed before jumping in. This will greatly improve you odds of getting this guy in your log. The convention seems to be to work split “up” on the USB bands and “down” on the LSB bands. Answer

by ron-j.-kd2eqs

Another advantage of the “split” comes from the US Extra test material. The DX station can call CQ on a frequency that may be out-of-band for broadcast for a lower license class (say General/Technician) OR for other countries which may have a slightly different band limit (but who can still listen to the CQ call frequency). And the CQ station can listen on the lower or higher split frequency which the responding station is licensed to transmit on. This allows use of additional frequencies in a crowded DX environment.

For example, DX station calls CQ on 14.220 MHz and listens “up 10” which is at 14.230 MHz. In the US, the General Class license is authorized only above 14.225 MHz - this would allow the General Class (and higher) responders to transmit on a valid frequency while listening on what otherwise only a higher US class would be able to transmit on. Tags: contest (Prev Q) (Next Q), frequency (Prev Q) (Next Q)

Q: I hate contests. How can I avoid them? Tags: contest (Prev Q) (Next Q) There’s nothing worse to getting home, turning on the radio, and being unable to find a clear frequency that isn’t full of a bunch of meaningless QSOs where somehow everyone is 599 and no one has anything to say. Are there any designated “contest-free zones”, or other ways I might be able to enjoy amateur radio without contests? Tags: contest (Prev Q) (Next Q) User: phil-frost Answer

by adam-davis

Most countries follow the band plans that disallow contesting on WARC frequencies, which include three narrow slices of shortwave frequencies at 30M, 17M, and 12M. If you stick to these frequencies you will rarely, if ever, be bothered by contests. It’s a small slice of spectrum though, so you might simply consider doing what some amateurs do and simply note the days the contests are operating, and plan activities other than amateur radio on those days. Given that most contests are short duration, occur mostly on weekends, and don’t occur more than a few times a year, it’s not unreasonable to simply avoid affected bands on affected days. Tags: contest (Prev Q) (Next Q)

Q: Are there ways for people with receivers to participate in contests? Tags: contest (Prev Q) (Next Q), receiver (Prev Q) (Next Q) At the moment I only have an HF receiver (or I will when I build it, hopefully soon). Are there any contests I can participate in, or ways for me to participate in a contest without borrowing a transmitter or working with an amateur who has one? Tags: contest (Prev Q) (Next Q), receiver (Prev Q) (Next Q) User: adam-davis Answer

by walter-underwood-k6wru

Summits on the Air (SOTA) is not a contest, but an ongoing activity with awards. You can participate as an activator (transmitting from summits), a chaser (working those on

summits), or an SWL (listening to contacts and logging them). All the chaser awards are available to SWLs (shortwave listeners). More info is here: Other activities also have SWL awards. There appears to be one for IOTA (Islands on the Air). This site is dedicated to “shortwave amateur radio listening” and has a news about awards and a registry: Tags: contest (Prev Q) (Next Q), receiver (Prev Q) (Next Q)

Q: Can a 1A Field Day station qualify for the “Alternate Power” bonus? Tags: contest (Prev Q) We just finished our Field Day operations, and we’re having a disagreement on whether we qualify for the Alternate Power bonus. Our 1A (single transmitter, emergency power) station was completely solar powered for the duration of Field Day, which seems like it should qualify us for the bonus, but the wording of the 2014 rules makes it sound like it must be a separate effort from the main system. 7.3.8. Alternate Power: 100 bonus points for Field Day groups making a minimum of five QSOs without using power from commercial mains or petroleum driven generator. This means an “alternate” energy source of power, such as solar, wind, methane or water. This includes batteries charged by natural means (not dry cells). The natural power transmitter counts as an additional transmitter. If you do not wish to increase your operating category, you should take one of your other transmitters off the air while the natural power transmitter is in operation. A separate list of natural power QSOs should be submitted with your entry. Available to Classes A, B, E, and F. Can a 1A station qualify for the “Alternate Power” bonus? Tags: contest (Prev Q) User: w5vo Answer

by pete-nu9w

Of course you get the 100 points. You only used one transmitter, so there wasn’t an issue of using more than your classification allowed. What the next-to-last sentence of that paragraph is getting at, somewhat sloppily, is operations that only used alternate power briefly to make their 5 QSOs. For example, our group was 2A, using two transmitters full time under emergency power from a generator. For about an hour we took one of those transmitters off the emergency power and connected it to solar-charged batteries for the Alternate Power bonus. If we had kept going

with two transmitters and added an alternate power transmitter we would have been using three transmitters, violating our 2A classification. EDIT: the reason for pointing out that it counts as a transmitter is that some transmitters don’t count. Neither the GOTA transmitter nor a transmitter used for satellite communications counts as a transmitter for determining the category. Tags: contest (Prev Q)

Mobile Questions Q: FM radio in car gets interference from APRS beacon Tags: mobile (Prev Q) (Next Q), rfi (Prev Q) (Next Q) The FM broadcast radio, factory installed in my car and usually tuned to 88.6 MHz, gets some interference from the 5W APRS transmitter on 144.800 MHz. It sounds like if the sensitivity of the broadcast FM receiver would go down a bit temporarily: more static FM noise is heard during the APRS “brraaap”. The effect is more pronounced when I’m far away from my favourite station’s transmitter and the signal is already weak. When I’m in town, it’s barely noticeable. The APRS transmitter has a properly mounted antenna (hole-through-roof, 1/4 wave vertical). The broadcast radio of the Volvo V70 does not have visible external antennas there’s one painted on the left trunk window, and apparently a second one embedded within the back right light assembly. What can I do to fix this? Tags: mobile (Prev Q) (Next Q), rfi (Prev Q) (Next Q) User: oh7lzb Answer

by adam-davis

There are a few ways the noise could be transmitted to the car radio, and the way to fix it will depend on how it’s getting in there. 1. Antenna 2. Power or ground 3. Other EMI If the transmission is swamping your radio’s receiver, then it’s not blocking the higher frequencies strongly enough. It might be worth looking at the output of the transmitter to see if it’s broadcasting noise on other bands within the radio’s region, and to take another transmitter that’s not connected to the vehicle’s power or ground and keying it up nearby. If it disturbs the radio, then it’s likely that the radio may need to be replaced. Other options would be a different antenna. If the transmission is coming through the power or ground, you might be able to add additional filtering and regulation at the radio. This can be tested by attaching a dummy load to the transmitter while it’s transmitting. If the noise is present, it’s likely EMI or power conduction. Again, keying a separate radio outside the vehicle may narrow it down. Alternately, connect the APRS transmitter to a battery power supply and disconnect it

from the car’s power supply. It’ll still be grounded to the car, but it should narrow things down a little more. EMI is a tougher one without a spectrum analyzer. If the transmitter and radio are far apart, though, and each have their own metal case, it shouldn’t be the cause. I’d look for antenna and power problems first. Tags: mobile (Prev Q) (Next Q), rfi (Prev Q) (Next Q)

Q: Is there an optimum Antenna Feedline Length for mobile installations? Tags: mobile (Prev Q), coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) I bought a ham radio antenna mounting kit for my car that includes ~16’ of coax. One end has a trunk lip NMO antenna mount, the other end has a re-solderable PL-259. I asked the sales person if it is best to shorten the coax after installation to only the length required to reach the radio transceiver and they said “I would just leave it, the length is already optimized for maximum efficiency at the factory”. I’ve heard of this before (mostly from CB Radio installers) but don’t actually know if this is true or understand why/if there is an optimum feedline length for VHF/UHF FM use (vs Citizen’s Band AM HF). I intend to be setup for both VHF/UHF but will operate primarily on 2M VHF and so any trade-offs should be optimized for the 2M band. My SWR on 2M at my club’s repeater frequency is 1.7. Would shortening the length change the SWR or only change the losses incurred due to the SWR? I have a nice space in the trunk, normally used for a sub-woofer if you purchased an optional “premium stereo” with the car - in my case this space sits empty. I plan to keep the radio transceiver body in the trunk with the remote head unit up front. This would allow me to keep the antenna feedline shorter and make for an aesthetically clean installation. This would also allow the antenna feedline length to be something around 56ft if shortening it would be beneficial (although I could just coil up the unused ~10ft or so). Tags: mobile (Prev Q), coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) User: benswayne Answer

by phil-frost

In the absence of common-mode currents, then the optimum feedline length is 0, because a longer feedline only increases your feedline losses. These losses are due to the resistance of the wire, dielectric losses, etc. and are specified in dB per unit length in the coax datasheet. At VHF and up, these losses can be significant even at car lengths, especially with less expensive or smaller feedline. When you do have common-mode currents , then the feedline is effectively part of the antenna. Changing its length does the same thing as changing the length of the antenna: it can alter the radiation efficiency and impedance (and thus SWR) of the antenna. Even in this case, it’s hard to say just what the “optimum length” is, because feedlines tend to be routed to, around, or near other conductive objects (like the radio chassis, and through the negative power supply lead, the car body), and these too will alter the operation of the antenna. There’s nothing special about CB: it’s still just radio, and a properly designed and installed station still has no significant common-mode currents, and the feedline should still be a

short as possible. The issue is that CB operators have more interest in superstition than a proper understanding of RF engineering. A popular CB antenna is a vertical which is installed with no ground plane, or an insufficient ground plane. In this case, the feedline acts like the missing half of the dipole, so the feedline length absolutely is essential to the operation of the antenna. While you can indeed “tune” your “antenna” in this case by altering the feedline length, this is usually bad advice. Addressing the common-mode current problem , rather than fiddling with feedline length until you happen to get a good antenna, usually yields a more robust and predictable result. Tags: mobile (Prev Q), coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q)

CW Questions

Q: Where can one find recordings of Morse code, generated by humans and not machines? Tags: cw (Prev Q) (Next Q) I need some recordings of CW / Morse code for use in a project. Most of what I find is either nonsense (it just exists for the ‘sound of CW’, but doesn’t contain a message) or is generated by a computer. Where can I find some audio of real CW operators? I’ve been scanning the HF bands but have only found beacons, which are obviously computer controlled. Tags: cw (Prev Q) (Next Q) User: horse-hair Answer

by hotpaw2

Wait for a Straight Key Night ( the CW portion of HF bands. Answer

) to record from

by pidloop

Another source of hand-keyed CW is the SKCC ( ) 40m calling frequency at 7.050 MHz where you can hear code from straight keys most evenings (US). There is even more activity during their monthly sprints starting at 0000 UTC the fourth Wednesday of each month (Tuesday evening the US). Regarding CW analysis, you might be interested in the thread which roughly starts here . It goes on for over a year but contains excellent insights in several aspects if CW timing, noise reduction and decoding techniques. Tags: cw (Prev Q) (Next Q)

Q: Shaving Quartz Crystal for New Frequency Tags: cw (Prev Q), oscillator (Next Q) Back in the 1960s during my Novice days I operated on the 40-meter band only with 4 different quartz crystals that determined my transmitting frequency with my Eico 720 CW transmitter. I had heard about other old-timers who would shave (or something, not sure of the actual act) the crystals to shift the frequency by small amounts, maybe up to 10 KHz (or, back then it was 10 KC). Has anyone done this and if so do you know how it was done. Did they change the dimensions merely by sanding or something or did they actually cut the crystal. At that time, most of the quartz crystals were in a packaging known as FT243 and this packaging allowed the crystal to be taken apart by unscrewing the package sides and removing them.

Today, I have a number of old-style FT243 quartz crystals that I would like to experiment with just for the fun of it but I would like to know more about the process before I start. [Note: none of the tags are specifically fitting that I can tell so I picked two that might hint]. Tags: cw (Prev Q), oscillator (Next Q) User: k7peh Answer

by dave-tweed

It is the thickness of the crystal that primarily determines its operating frequency. When crystals are manufactured, they are gradually ground down in a special fixture. The operator monitors the process by keeping a shortwave radio nearby, which picks up the electrical noise created by the stress of the grinding action on the crystals, which is relatively narrowband noise centered on the resonant frequency. When this gets to be slightly above the target frequency, the grinding process is halted. The next step is to plate electrical contacts on the newly-ground faces of the crystal so that it can be mounted in a holder. The thickness of this plating affects the final frequency (thicker plating reduces the frequency), and this is how the final calibration of each crystal is accomplished. If you want to adjust (lower) the crystal frequency after it has been completed, you can try adding additional mass to the contact areas. I don’t know any easy way to raise the frequency. Tags: cw (Prev Q), oscillator (Next Q)

RFI Questions Q: How do I prevent radio signals from popping a GFCI plug? Tags: rfi (Prev Q) (Next Q), grounding (Prev Q) (Next Q) My wife woke up several nights by a metallic “thunk”. It happened to be while I was talking on 10 meters and turned out to be the ground fault circuit interrupter (GFCI) on her hair dryer cord. Apart from the obvious answer of leaving it unplugged, I’m looking for a solution to preventing this because I’m concerned there are other effects of which I’m not aware. At the time, I had not completed the grounding of my newly set up shack. I’ve since established an earth ground using a backup water well point pipe in my basement (it’s electrically isolated from the pump by a PVC connect pipe and is hardly used so I’m not worried about regular interference from that). Unfortunately, the 12v supply for the HF radio doesn’t seem to have a ground stud on it so I can’t ground that apart from the regular mains cord ground. The antenna mast is grounded to a typical 8ft ground rod using a 6AWG wire. But despite my efforts at proper grounding, the problem still occurs. Is the GFCI tripping due to improper grounding or possibly due to RFI (which additional or better grounding wouldn’t necessarily fix)? And how could this tripping be prevented? I’m concerned that whatever is causing this could be affecting other more sensitive (and expensive) devices in the house. (Note that this is an older house - 1960s - and doesn’t have any GFCI breakers or outlets where I’d expect there to be any such as the outside, garage or kitchen. So I can’t report on similar behavior in other GFCIs.) Tags: rfi (Prev Q) (Next Q), grounding (Prev Q) (Next Q) User: peter-kb1avl Answer

by bill–k5wl

Some older GFCI circuits were known to be susceptible to stray RF. The ARRL recommends replacing these older breakers with new ones that they have listed at the link I provided. Answer

by phil-frost

It’s true, some GFCIs are just abnormally fussy, and you can attenuate RF on a conductor with ferrites. However, a lot of amateur setups have improperly designed or installed antennas. Common-mode RF currents in the antenna feed system will travel right down the feedline,

to your transmitter, down its power cord, and into every other device in your house which is connected by the mains wiring, including all your GFCI outlets. Your house, and all the wiring in it, is essentially an oddly shaped radial, and RF currents will use it, if you don’t do something to stop them. A GFCI is effectively a common-mode current detector. When an electrical device isn’t electrocuting someone, the current on the hot conductor is exactly balanced by current on the neutral conductor. That is, there is no common-mode current. When you are holding a cold water pipe with one hand, and a faulty hair dryer with another, now some of that current can return to ground through the water pipe. Now the currents on the hot and neutral conductors aren’t balanced: there is a common-mode current. The GFCI concludes someone is being electrocuted, and opens the circuit. Of course, a GFCI can’t tell if the common-mode currents are due to you being electrocuted, or exist because your antenna finds your house’s wiring as a favorable RF return. It pops either way. So, before you go off replacing your GFCIs, or getting crazy with ferrite beads behind the walls in all the rooms, I suggest you look at your antenna feed. See Using a balun with a resonant dipole . The problem is equally applicable to verticals also: if your antenna isn’t on an ideal, infinite ground plane, you might need a balun anyway. Same goes for loops, or any other kind of antenna. Eliminate (to the extent possible) the common-mode currents at the source (your antenna) first. Tags: rfi (Prev Q) (Next Q), grounding (Prev Q) (Next Q)

Q: How can I reduce the noice coming in from an RTL-SDR dongle? Tags: rfi (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q) I’ve recently received an RTL-SDR dongle, and I’m picking up a lot of noise that is probably coming from my PC, especially a lot of “spikes” on the 2M band. I’ve already started using a USB extension cable instead of plugging the dongle into the PC. What else can I do to reduce the noise floor and get rid of the RFI on 2 meters? Tags: rfi (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q) User: krzysz00-kf5soq Answer

by kevin-reid-ag6yo

Here is an assortment of common ideas and recommendations for RTL-SDR devices: Mount the device directly on your antenna, or otherwise minimize the amount of feed line used. (This does not directly remove noise but rather increases signal, but that’s just as good if not better. It may also remove noise by moving the device further from your computer equipment.) Of course, if your antenna is outdoors you will need a weatherproof enclosure, and you must make sure the USB line meets USB specs despite its increased length (such as by using an active extension cable

designed for the purpose). Make sure you have the RF gain set correctly! Too little gain will bury real signals in the noise floor; turn it up until you see the noise floor rising a bit so that you’re seeing the noise from the antenna . Too much gain will overload and produce duplicated signals across the spectrum; turn it down until those extra spikes go away. I have found that the built-in AGC may err in the direction of too much gain. Build a shielded enclosure around the device; they come in plastic cases with no RF shielding at all. Add snap-on ferrite beads in ferrites.

near the ends of cables, if they didn’t come with built-

An RTL-SDR-specific suggestion I have frequently heard is to modify a USB extension cable by removing the shield at the female-A end. (One could also modify the device’s male-A plug but that might interfere with the mechanical connection.) The argument given is that the ground and shield are tied together on the PCB, and by disconnecting the USB cable shield from the ground you prevent noise carried on the outside of the shield from entering the RF section’s ground. I have not yet tried this modification myself, and a few comments here suggest it is not worthwhile. Tags: rfi (Prev Q) (Next Q), rtl-sdr (Prev Q) (Next Q)

Q: How would operating a ham radio affect other wireless devices in my house? Tags: rfi (Prev Q) I am interested in getting into ham radio however one of my concerns is could a ham radio affect current wireless communications in my house. I am particularly concerned when it comes to WiFi signals. Where I would likely put a radio, I currently have my computer which connects via WiFi to my router. I am concerned that if I set up a radio with an antenna on the roof above me, I could create interference for my already spotty WiFi signal. Is this a potential risk? Tags: rfi (Prev Q) User: rob-rose Answer

by paul

Well, mostly no but yes it is possible for the antenna to have an effect. No. I get more interference from wifi than interference to wifi.

In the computer adjacent to my ham station, I have had lockups but the network does not drop. It is not wifi related. I assume the lockups are from RF entering on a supposedly shielded cable like a USB mouse or keyboard cable. It happens rarely now that RFblocking clip on toroids are on the shields of these cables. Interference from a D-Link to the HF radio receiver was only partially reduced by wrapping the D-Link in Alumnium foil (except for the antenna, of course) and adding toroids to the ethernet and power lines. Routers can be noisy and some comparison shopping or additional internet questions may be in order. Yes Any large metal object around your house, an antenna, a refrigerator, a metal table, your car in the garage, metal such as steel studs in the walls or floors … will reflect the microwaves from your wifi. The level of wifi signal at a particular spot is affected by these reflections. This doesn’t have anything to do with talking on the ham radio, we are just talking about microwave reflections off of passive metal objects. As far as talking on the ham radio goes, the frequency for Wifi is 2.4Ghz or 5Ghz, which is quite different from the frequencies for most ham radio 1.8 - 432 Mhz. So they don’t typically interfere. Also, interference temporarily slows down Wifi, it doesn’t typically stop wifi unless somehow the router stops operating. The transmission protocol of Wifi immediately resends information that was missed due to any reason (weak signal, interference from neighbors’ wifi, etc) without action by the user. If you have ancient 1980s era 49 Mhz cordless phones or 49 Mhz baby monitors, get rid of those. Some amplified speakers — like computer speakers — may receive you when you talk. This does not indicate any fault, and is normal. It is the speakers that are the problem. If you share your living situation with apartment neighbors or a home with a family or significant other, perception can be more important than fact. Perhaps strengthen the wifi first, and then worry about ham radio. That being said, a variety of wifi routers and wifi antennas can be had for around 100 US dollars, and often less, that, by trial and error, might improve your existing signal levels. The typical $30 wifi router does not have a very powerful transmitter and you might pay attention to the output power (usually in milliwatts) if you upgrade it. Some people build focused wifi antennas out of various food cans or flashlights to obtain a gain in signal. The construction of these wifi antennas is more of a do-it-yourself hobby among wifi hobbyists than necessitated by anything about ham radio. Tags: rfi (Prev Q)

Impedance Questions Q: Impedance Matching Different Feedlines Tags: impedance (Prev Q) (Next Q) (I promise there will be a question in this wall of text. I’m just giving context.) I’ve been wanting to try my hand at building my own antenna system for the last few weeks and in doing research, a number of questions came up. In particular, matching transmitters, feed lines and antennas in order to create a fully balanced system. This site, run by W5ALT , gives a great overview on why different systems need to be impedance matched in order to function properly, as well as consequences of improper impedance matching. I therefore understand why a balun would be used for coax feeding a balanced dipole, both for balance and impedance purposes. I also went about researching different antennas for portable use. Stackexchange led me to the October 1984 QST article on a full-wave delta loop. One of these setups (see following image, part B) describes a 450-ohm ladderline going into a 100-ohm feed point on the loop.

On this site , the author says to NOT use a balun between the 50- or 75-ohm coax feedline and the 100-ohm feed point: Don’t use a Balun on this Antenna! On a horizontally oriented loop you can feed a corner, center of a side or anywhere it is unimportant. I also have a folded dipole fed directly by ladderline (Cobra Ultralite Sr.) that functions quite well (I busted through a pileup for a Portuguese contest; it can’t be that bad). It is fed by 50-ohm coax from a tuner into a 1:4 balun to the ladderline. From various sources on the internet, the typical impedance of a resonant dipole is roughly 73 ohms . A folded dipole will increase this impedance to the square of the number of parallel elements (for the ultralite sr. with 3 parallel elements, I calculate 9 * 73 = 657 ohms impedance). The feedline could very well be 600-ohm ladderline (I am not sure; the line is not marked with impedance). So my question is this: in particular, why does the W1FB full-wave loop design not require some form of a transformer between the 450-ohm ladderline and the 100-ohm antenna? My research tells me it’s obvious that having matched impedance would allow more efficient power transfer from the feedline to the antenna. Is it because ladderline is balanced? Is that kind of impedance mismatch allowable? Is it a rule that you don’t need a balun for ladderline? Is it purely a choice by the designer? I’m familiar with the subject of electronics, but I’m certainly no electrical engineer, so the theory behind this just seems to contradict practical examples. Thanks for any and all help. I’ve been trying to find a reason for this for days and nothing seems logical to me. Tags: impedance (Prev Q) (Next Q) User: italic_ Answer

by phil-frost

It doesn’t make sense because people on the internet are wrong or misinformed, present conflicting information, or just plain don’t know what they are talking about. Impedance mismatches aren’t the end of the world. An impedance mismatch does not, in itself, cause power loss. It causes power to be reflected, at which point it will go in the other direction until it’s either absorbed or encounters another impedance mismatch which reflects it back at the antenna. When it gets back to the antenna, some of that power is radiated, and the rest of it reflects back and forth again until its all radiated. In fact, if you had a lossless transmission line, impedance mismatches wouldn’t matter at all. Each parcel of power would just reflect back and forth until it’s radiated. We can’t have lossless transmission line, but we can keep losses very low. One way is to buy good coax. Good coax is expensive. Another way is to use ladder line. For the cost, ladder line has lower loss than coax. Interestingly, a piece of transmission line can be used as a transformer. If that transmission line is 1/4 wave long, it’s called a quarter-wave transformer , and it makes whatever’s at

the end of it look like the conjugate impedance. That’s part of what’s going on in some of these antennas, but there’s a problem… Whenever you hear someone say “don’t use a balun”, you should be thinking: 1. they may not have a good understanding of RF engineering, and 2. the feedline is actually part of the antenna See Using a balun with a resonant dipole . You absolutely can feed a dipole without a balun, but you have to understand that if you do it, the coax is as much of the antenna as the balun. This means anything you read about dipoles (like, their radiation pattern, feedpoint impedance, etc) does not apply. It doesn’t necessarily mean it’s a bad antenna, it’s just some other kind of antenna which might be good or bad. Since the geometry of the feedline is different at each station, it doesn’t mean anything. It just means you don’t know. Be especially dubious when you hear “don’t use a balun” in combination with “multi-band antenna”. One way to make a multi-band antenna is to design the antenna such that there are a lot of common-mode currents on the feedline, thus making the feedline in effect a long-wire antenna . The “antenna” is really just a distraction: the feedline does most of the radiating. There are quite a few antennas that dubiously work this way . I hope that addresses your concerns enough. I can’t really explain every question you have (that would be an entire book on antenna design), but regardless there are some good lessons to be learned here: the internet can be wrong, especially when hams are writing about antennas, your intuition about things not making sense is well-founded, and the best way to learn how things really work involves a good deal of skepticism. Tags: impedance (Prev Q) (Next Q)

Q: Will measuring SWR through a feed line mislead me? Tags: impedance (Prev Q) I know that except in the perfectly matched case, transmission lines transform impedances along their length; if I measure the impedance at the other end of my feed line, or even with a short jumper between my antenna analyzer and the antenna, I won’t be reading the true impedance of the antenna (or other device at the end of the line). Will the impedance transformation ever make an actual mismatch “look good” (1:1 SWR)? Tags: impedance (Prev Q) User: kevin-reid-ag6yo


by phil-frost

In an ideal world, if the characteristic impedance of your transmission line matches the system impedance (usually 50Ω), then adding or removing lengths of transmission line just moves the complex impedance around a constant-SWR circle. So you may get a different impedance (it may look capacitive instead of inductive, etc), but the SWR will always be the same, regardless of how much transmission line is between your meter and the antenna. However, the real world is not ideal. Firstly, if the transmission line is lossy, that will make the SWR better. It does so because the transmission line absorbs some of the transmitted energy, and then absorbs again the reflected wave. No reflected wave means 1:1 SWR. Absorbing all the energy is one way to reduce the reflected wave. Secondly, there are a great many amateur antenna designs which, intentionally or not, use the feedline as part of the antenna . These antenna currents on the feedline are called common-mode currents. When they exist, the feedline is very much part of the antenna, and changing the feedline length can change the impedance of the antenna, just like changing the length of any of the other antenna elements would. For this reason and many others, good antenna designs do not have significant common-mode currents. Answer

by kevin-reid-ag6yo

No, the SWR will remain high (in fact, constant) no matter how much line there is between the meter/analyzer and the antenna, assuming the line is matched to the meter. An argument that this must be the case, skipping the math: 1. Instead of considering the impedance of the antenna and how it is transformed along the feed line towards the transmitter or meter, work from the other direction. The transmitter has a standard 50 Ω (or whatever) impedance, and the feed line also has a characteristic impedance of 50 Ω, so we know the impedance observed at the other end of the line itself must be 50 Ω. 2. Therefore, if the antenna feed point has an impedance other than 50 Ω, there is a mismatch at that junction. During transmission, this mismatch will, as mismatches do, reflect some of the signal, which will propagate all the way back down the feed line, and be observable at the transmitter end. 3. Therefore, if we substitute the analyzer for the transmitter, it will detect the mismatch. You won’t see the same complex impedance as you would without the line in the way, but you’ll see the same SWR. There is a caveat here: the feed line has some loss, and that loss will tend to make the mismatch look less bad because it absorbs power in both directions, resulting in less reflection. But if you have a significant amount of such loss, then you have a worse problem than bad SWR. If you did want to compensate for the effect of the transmission line, or generally to

visualize this situation, the tool for that is a Smith chart purpose:

. On a Smith chart, for this

The center point corresponds to the characteristic impedance, and all other points to different impedances. Distances from the center correspond to SWR. Adding a length of transmission line corresponds to rotating by an angle about the center of the chart. Tags: impedance (Prev Q)

Transceiver Questions Q: How can I get started with a Home Brew QRP? Tags: transceiver (Prev Q) (Next Q) I want to build a simple 40 meter CW transmitter and Receiver pair. What should I do to get started into home-brew HF RF devices? Tags: transceiver (Prev Q) (Next Q) User: skyler-440 Answer

by k9krb

I built a BitX 20a , which was fairly complex, but a really neat kit. If your soldering skills are ok, and you can wind small wire through tiny donut shaped cores, you will have a lot of fun. The SMK-2 40m kit might meet your needs (40 meter CW), but it’s surface mount. Don’t be afraid of that, with a good magnifying glass, and some inexpensive chinese made soldering tools and some solder paste, it’s easy. I also built a Sudden Storm that might be a good fit.

from KF5OBS

. They have several simpler, small kits

I’ve found kits a great way to learn. I learned a lot trying to get my BitX to work, I found a few errors I made, but I learned a lot about the theory in the process. Don’t be afraid to learn as you go! Tags: transceiver (Prev Q) (Next Q)

Q: Why do so many HF transceivers use a UHF connector? Tags: transceiver (Prev Q) (Next Q) Just looking around at various rigs online for a fiend. Lots of them look really attractive TS-480, K2, K3, FT-450D, FT-950, IC-78, FT-897 to name just a few… These rigs are mostly HF, albeit some are also VHF/UHF capable. Yet the antenna connector used is usually either PL259, or SO239. Both mentioned connectors are known UHF. What is the rationale behind having a UHF connector attached to an (essentially) HF rig?

Is it merely a matter of cost/convenience as listed in Pros/cons of the PL259/SO239 connector (M type)? ? Tags: transceiver (Prev Q) (Next Q) User: vu2nhw Answer

by oh7lzb

The “UHF” PL259/SO239 connector , which was originally designed at World War II times as a shielded banana plug is actually not a very good connector to be used on UHF frequencies, due to its non-continuous impedance and other properties. The common name is a bit misleading, since it’s old - at the time of the design, UHF referred to frequencies above 30 MHz, and by today’s standards UHF is 300 MHz to 3 GHz. This measurement shows 0.2 db insertion loss at 144 MHz and 1 db insertion loss at 432 MHz, and with low-quality connectors (or higher frequency such as 2.4 GHz) it would be worse. The connector works fine on the frequencies it was designed for: HF and VHF. Most modern HF rigs come with these connectors mostly because it has become an industry standard for amateur HF transceivers, and it works. It might not be the best connector on the face of the earth, but everyone already has them on their rigs, cables, amplifiers, tuners and antenna switches. When someone produces an HF rig with some other connector, most users will have to use adapters or build adapter cables. Cost, convenience, standard solution. Tags: transceiver (Prev Q) (Next Q)

Q: What is a waterfall display? Tags: transceiver (Prev Q) (Next Q) High-end transceivers apparently come equipped with a water-fall display - something to do with improved spectrum visibility. This is supposed to lead to potentially higher QSO count and rate. What is a waterfall display? Tags: transceiver (Prev Q) (Next Q) User: vu2nhw Answer

by michael-kjörling

A waterfall display is a graphical representation of the signals across a frequency range, generally color-coded to indicate signal amplitude or strength, displayed over time.

image source: ARRL

and K2NCC

Pictured in the image above is a number of signal traces. Since the above was taken across a frequency range where PSK31 is used, the signals are very narrow (only a few tens of Hz wide each), but it could easily cover a much larger frequency range “zoomed out” and still look basically the same. Here, black and dark blue is basically background noise, and bright white represents a very strong signal. We can also see that the station around 2450 Hz into the receiver passband appears to have insufficient sideband suppression (notice the additional, weaker signals centered on the main signal frequency). Having an overview of all signals across a portion of the spectrum allows you to quickly and easily determine whether there are any strong signals, which usually indicates stations that would be easy for you to make contact with. Not having to scan across the band to locate any station that might happen to be transmitting at the exact moment you pass over its frequency but rather being able to locate stations transmitting while you are working another station, means that you can immediately jump to the frequency when you are done with the previous station. Tags: transceiver (Prev Q) (Next Q)

Q: What makes a good emergency-capable QRP rig for travel? Tags: transceiver (Prev Q) (Next Q), emergency (Prev Q) (Next Q) It’s wintertime, which drives the concept of emergency preparedness here above the 45th Parallel. Am emergency-capable QRP rig is an excellent item to stuff into one’s Go Bag or

vacation gear, always but especially now. What’s an essential minimum for a QRP HF rig suited for rural (no-repeater)? Tags: transceiver (Prev Q) (Next Q), emergency (Prev Q) (Next Q) User: k7aay Answer

by wprecht–ab3ry

This is a huge area and personal preference is going to drive the choices to a great degree. For a good answer some parameters need to be defined: Are you only going to operate the rig if you are in trouble? This defines the size/cost/weight of your choice. If you are going to also operate “normally”, the rig can take up more of your space/weight budget. If you intend to only operate in emergencies, then something small and light is probably best. What mode will you be using? CW, SSB, or both? Define travel. Are you going to be on foot, horseback, dog sled, snowmobile or other motorized transport? Obviously this makes a huge impact in the weight and size categories. Anything other than on foot realistically opens you up to just about any portable transceiver. On foot, then something small with small (light) batteries is appropriate. But the size there depends on how far you are going and if you will operate at other times than an emergency. Who would you be trying to reach: other preppers, State Troopers, Alaska National Guard SAR, USCG, Mom and Dad? How far away are these people and what are the conditions (propagation-wise, in general) you will face where you are going? This would define the capabilities needed in your rig. Your cute ¼W 40m CW only Tuna Tin II won’t do you much good for contacting the State Troopers, for example. I don’t have a “go bag”, I live on the coastal plain between Baltimore and DC and there’s no hope to escape the region for a sudden event. And if it’s not sudden, I have time to pack and being an organized individual, I could probably still get out of the house faster than many with prepared plans. If I did live away from large cities with only 1 or 2 roads out of the area, my bag would look like this: 1) My Android Smart phone with spare batteries. This has the usual assortment of apps loaded including a repeater listing app that only requires your GPS fix, not a connection to the network, to function. Gives you bearing and range all repeaters in 25/50 miles depending on the setting. 2) SPOT Personal Tracker — 99USD MSRP. This is a GPS / Satellite unit that you can use to check in as OK or to summon help. Uses commercial satellites to route “911” calls to the nearest SAR outfit to your location. They make larger units that also function as regular GPS devices. I wouldn’t hike outside of cell coverage without this or something similar, emergency conditions or not.

3) Cheap Chinese 2m/440MHz HT. I have a couple. These are small, light and so cheap and useful, even if you have a nice HT, having a few of these around is handy and at $35 each they are some of the cheapest ham gear you could own. 4) Small folding Yagi for 2m and/or 440MHz. These weigh almost nothing when made from an old tape measure and take up no room. With one of these, the Chinese HT and the repeater book off the phone, the chances of hitting a repeater just went up dramatically. After that it would depend on answers to the above questions. For me the answer is my FT-817. It’s hard to beat the DC to daylight coverage including the 5MHz Alaska Emergency Frequency. For casual use or emergency only use, the internal batteries are all you need. I have the W4RT NiMH pack in mine and it lasts me for hours. If I want more time, I have a pair of NiMH packs from RC planes that I have set up with power poles. Together the 3 packs last me 15-20 hours. It has an internal keyer, so add a set of travel paddles, a 20m dipole and a VHF/UHF dummy load, I mean rubber duckie and I am set. I can use the dipole on 40m and 10m with acceptable SWR in a pinch. If we are talking non-foot travel, then adding a tuner would be good. Perhaps other antennas, my BuddiPole/MFJ vertical has given me contacts out to a couple thousand km at 5W. the whole thing packs up to about 70cm long and 1-2kg. YMMV, but here’s a start. Tags: transceiver (Prev Q) (Next Q), emergency (Prev Q) (Next Q)

Q: Adapting an antenna coupler Tags: transceiver (Prev Q) (Next Q) I’ve built AA5TB’s antenna coupler


I left out C2 because I didn’t understand why I would need it - why would I? It works fine without. Unfortunately, when I started tuning for a 5W 20m transceiver, the LED was on all the time. I then measured with a multimeter the AC voltage over the LED, and tuned to its minimum, about 3.2V~. The maximum was about 4.2V~. I was thinking of changing R4 and/or R5 so that these extremes are a bit lower. Is that the right way to do this? I’m worried, because I’d say the resistance of the whole R4-R5-D2 circuit should be about 51 Ohm, like the other resistors. Or would adding C2 resolve this issue? Tags: transceiver (Prev Q) (Next Q) User: camil-staps Answer

by phil-frost

C2 removes the AC component across the LED, and prevents the LED from being on when the antenna is matched to 50 ohms. You say the circuit works anyway — probably at QRP levels it’s not bright enough to see. I bet if you try it in a dark room, or with a higher power transmitter, you will see it. Anyway, consider how this circuit works. Here’s a simplified version which makes the antenna impedance more explicit, and lacks any sort of visible indicator:

simulate this circuit

– Schematic created using CircuitLab

This is a Wheatstone bridge unknown value (R ant ).

. V1 is your transmitter, and the antenna is the resistor of

Think of it this way: R 1 and R 3 form a voltage divider, and R 2 and R ant form another. D1, C1, and R5 make a peak detector. If R ant < R 3 , then on the positive cycle of V1, the voltage at A is greater than the voltage at B, and C1 charges through D1 to the peak difference. If R ant > R 3 , then on the negative cycle of V1, the voltage at B is more negative than at A, and again C1 charges through D1. But if R ant = R 3 (50Ω, our target impedance), then there is no voltage between A and B, and so D1 can never be forward biased, and so C1 can have no voltage across it, except for a small AC component via R5. The time constant of C1 and R5 make a filter with a cutoff frequency of 1 1 fc = = ≈ 1600 kHz 2πRC 2π(10 kΩ)(10 nF)

This is so low far below the frequency of V1 that we can consider the AC component of the voltage across C1 to be zero. Instead, it appears across R5. So now, look back to your circuit with the LED. It is connected across R5, which has some RF voltage across it all the time. When C1 is charged because the antenna isn’t 50Ω then there is additionally some DC component, and it’s really this DC component that we are interested in. Remember, a capacitor looks like a low impedance at higher frequencies, so by adding C2, you are effectively shunting any RF current around the LED, so that the LED sees only the DC component. An alternate solution to this problem is to connect the LED across C1, like this:

simulate this circuit

For that matter, why bother with two diodes when you already have one? An LED doesn’t make a great RF rectifier, but I bet it works well enough at HF in this application. In fact, with one less diode drop of voltage I bet it’s even more sensitive. We don’t really need the capacitor since an LED flickering at 14 MHz looks just the same:

simulate this circuit

Adjust the value of R4 to get the right LED brightness for your transmitter power. One might ask why AA5TB’s design is the way it is, and I’m guessing it’s because that’s how someone else did it , and the design was just copied with minor modifications. R4 and R5 together used to be a potentiometer. The arrangement of connected the LED to ground instead of point B (thus requiring C2) is probably because the LED used to be a meter. If you have a meter with a metal casing, and you are building this in a metal box, it may be easier to connect the meter to ground than to isolate it from the enclosure. With an LED you have no such restrictions. Tags: transceiver (Prev Q) (Next Q)

Q: Antenna tuning while receiving Tags: transceiver (Prev Q) (Next Q) I’ve built AA5TB’s antenna coupler

for a 5W 20m transceiver.

Tuning was kind of difficult because my transceiver has buttons for sending a dot and a dash, but no tuning mode, so I couldn’t have the transmitter on permanently to tune easily. I had to tweak it a bit to make it do this. I also have a 7.017MHz calibrated transmitter. Would it be okay to put the transceiver in receive mode, on 14.034MHz, hold that calibrated transmitter close to the antenna, and tune until the signal is the loudest (or, until the LED doesn’t light / the voltage measured over D2 is in its minimum)? So in other words: can I tune the antenna when not transmitting?

Tags: transceiver (Prev Q) (Next Q) User: camil-staps Answer

by phil-frost

You can tune by receiving, generally. When your antenna is tuned, then SWR losses are minimized. By reciprocity this minimizes receive losses also, so you can just listen to noise and tune for maximum received noise level. In fact, with more complicated tuners that have more adjustments, this is usually the first step so that you can be in the right ballpark and avoid subjecting your transmitter to a really horrible match. Your proposed method of coupling another transmitter to this particular tuner has a couple of problems, though. Firstly, this device doesn’t really measure SWR, but instead is an impedance bridge which determines if the antenna impedance is 50 ohms. See the explanation of how the circuit works in another question, and it should be obvious how this won’t work without the transmitter. Additionally, if you put your calibrated transmitter “very close” to the antenna, then it will be coupling to the antenna in the near field , which has significantly different characteristics than the far field, which is what you care about for radio communication. Lastly, tuning is frequency dependent, so a 7.017MHz transmitter isn’t of much help for tuning 14.034MHz. You could probably find a way to make your transmitter generate a 2nd harmonic and filter that out, and then you’d have 14.034MHz. I have a much simpler idea: try increasing C1. If you increase it enough, it will be able to power D2 through the period between the dashes. You can also try increasing R4, which will make the LED less bright, but discharge C1 more slowly. To get an idea of the values you need, consider the time constant of R4 and C1, which you want to be on the order of the spacing between the dashes, which is around 60ms for 20 WPM. So: 1 kΩ ⋅ C1 = 60 ms C1 ≈ 60 μF The disadvantage of this modification is that the LED indicator will be less responsive to your adjustments. Tags: transceiver (Prev Q) (Next Q)

Q: What is the minimum signal strength I need to receive? Tags: transceiver (Prev Q) Let’s say a transmitting station is using a 8W radio with a J pole antenna. The cable connecting the radio to the antenna is RG-58A/U and is 25ft long. At 144.075MHz, the attenuation of the cable is 1.5dB. At 8W, the power from the radio is 9.03dB. Assuming no losses other than cable losses, the antenna is getting 7.53dB, or 5.66W.

Let’s now say the receiving station, 4 miles away, has the same setup (8W radio, J pole, and RG-58A/U). Assuming the gain of the two J pole antennas is 2.15dBi, and using the Friis transmission equation, the receiving antenna is receiving 1.733e-8W. With the cable losses of the receiving station being 1.5dB (1.41W), and the antenna receiving 1.733e-8W, it appears the received signal will never make it to the receiving station’s radio. Me and my buddy have this setup with Baofeng BF-F8HP radios. If we are both using J pole antennas, we cannot communicate with each other. If one of us is using a J pole and the other is using the stock rubber ducky, the rubber ducky user can receive the J pole user’s transmissions. I’m assuming the reason we cannot communicate with each other if we are both using J poles is because of the cable losses. Is this correct? If so, is there a way around this? Tags: transceiver (Prev Q) User: km4ntk Answer

by phil-frost

At 8W, the power from the radio is 9.03dB. With the cable losses of the receiving station being 1.5dB (1.41W), and the antenna receiving 1.733e-8W, it appears the received signal will never make it to the receiving station’s radio. This seems to be the crux of your misunderstanding. You can’t convert watts into decibels, or decibels into watts. A decibel expresses a ratio of two things. In the case of losses at the receiver, it expresses the ratio of the received power (before losses) to the output power (after losses). In the case of dBi, it expresses the ratio of the radiant intensity of a given antenna in its direction of maximum gain to the same of a hypothetical antenna which radiates equally in all directions. In the case of dBm, it expresses the ratio of some power to 1mW. So if your transmitter is 8W (that is, 8000mW), we can convert that into dBm: 8000 mW 8W = = 10 ⋅ log10 (8000) dBm = 39 dBm 1 mW 1 mW Notice how this is a ratio, and it is a unitless number because the unit (mW) cancelled in the second step. We add the “m” to “dB” to remember that the denominator is 1 mW. We can convert 39 dB back into a ratio: 39

10 = 7943 This ratio is telling us that something is 7943 times bigger than something else. 10

The “m” at the end of “dBm” reminds us that this is the proportion of some quantity in

relation to 1 mW, so to get back to the original quantity we must multiply by 1 mW: 7943 ⋅ 1 mW = 7941 mW ≈ 8 W The discrepancy is just rounding error. Really 8 W is closer to 39.03089986991944 dBm. If your receiver losses are 1.5 dB, then we can calculate the corresponding ratio (and I’ll use negative 1.5 dB, because it’s a loss): −1.5

10 = 0.71 Remember that’s a ratio: to get to some quantity we have to multiply it by something. In this case we are comparing the power delivered to the receiver to the power received by the antenna. So if the antenna was receiving 0.01 mW, then we’d do this: 0.71 ⋅ 0.01 mW = 0.0071 mW With this in mind, try your calculations again, and I think you will get a more sensical answer. 10

Tags: transceiver (Prev Q)

Coaxial Cable Skip to questions, Wiki by user dan-kd2ee Coaxial cables have two conductors separated by an insulator. The outer conductor, or the shield, wraps completely around the insulated inner conductor. A coaxial cable is typically utilized to connect a device to an antenna, or to another device. Questions should relate specifically to the properties of coaxial cables in general or a specific type of coaxial cable. Questions about connectors, including soldering or crimping, or about adapters are also on topic. Finally, questions can be about the use of coaxial cable to create baluns or other matching “circuits”.

Questions Q: What should I consider when choosing a coaxial cable? Tags: coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) Given a middling-power rig (up to 100 W) requiring a 50 Ω antenna, a few options for the coaxial cable with a 50 Ω impedance are RG-174 RG-58A/U RG-8 RG-213 Apart from cost, what factors are relevant in deciding which coaxial cable to use? Tags: coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) User: vu2nhw Answer

by pearsonartphoto

The most important thing about the cable is how much loss are you willing to accept in the feed line. Figure out how much cable you will need, and then determine what the loss on said cable will be. As I mentioned on my website , here’s a few good rules of thumb: Keep the power loss to no more than 3 db in the cable. If you can, use the same impedance as your antenna/transmitter, but always keep the impedance to within a factor of 1.5 of your antenna/transmitter. But really, match them, it’s not worth the hassle of mis-matched cable. If you can, use only a single strand of cable. Also, use the right connectors for both ends. Buy for the largest frequency that you think you will be using. Get a cable that is slightly larger than you need, but not excessively larger. The velocity factor only matters if you are trying to build a phase changing antenna. Longer cable equals more loss. Higher frequency is also more loss. Here’s a few websites that talk about what the loss is per length and frequency of each cable: osCsid=600b648260d42af6d62fe29eb5c9053d Answer

by bryan-leenheer

Your question is missing an important item; the frequency at which you’re operating. I work a lot of VHF+ contests, and all four of the varieties of coax you mention pose far

too much loss of signal to be viable for those frequencies. I use LMR-400 Ultraflex for 6 meter, and 3/8” Andrews Heliax hardline for 2 meter, 222, and 440 bands. presents at various frequencies.

is a great resource for tracking how much loss coax

Another point you don’t mention is where you’re intending to use the coax. Tower applications require different coax considerations than a mobile installation, and SOTA requirements are different still. Answer

by bill–k5wl

In addition to characteristic impedance (such as 50 ohms) and cost, which you’ve already considered, the two main factors for coax feed line types are line loss at a particular frequency, and velocity factor. The line loss varies depending on operating frequency, so it depends on your application. For line loss, the main factors are what frequency bands you’re going to use over the feedline, and how long the distance is between the transmitter and the antenna. For VHF and above, line loss is a much bigger consideration. Velocity factor comes into play if you are going to create matching stubs or if you are working with non-resonant antennas like the G5RV and need to avoid certain lengths. Other factors include how flexible the line is (braided vs. solid wire), how much motion it will endure (rotors, portable operations), how waterproof it is (permanent or underground installation), how hard it is to work with (LMR-100 is notoriously hard to attach connectors to), etc. Tags: coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q)

Q: 50 Ohm coaxial cable vs 450 Ohm or 600 Ohm ladder or window line? Tags: coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) What are the relative advantages and disadvantages of using 50 Ohm coaxial cable as opposed to 450 Ohm or 600 Ohm ladder or window line? Tags: coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q) User: timtech Answer

by on4aa

Cheaper & less loss The main advantage of two-wire transmission lines over coaxial cable is, apart from reduced cost, also much lower loss. This is because the dielectric in two-wire lines is predominantly air. Plastic dielectrics provide more loss. In that respect, open-wire line has the least loss of all two-wire transmission lines, window-line a bit more and twin-lead ribbon line even more so.

Loss measurements A classic paper by Wes Stewart, N7WS reports on loss measurements of 450Ω “Wireman” window-line . An impedance-matched, 100ft length of medium-grade type 552 windowline showed 0.24dB loss at 20MHz under dry conditions. In contrast, the ARRL Antenna Book reports for an impedance-matched 100ft length of RG-213 coaxial cable at the same frequency a loss of slightly more than 1.0dB. Additional mismatch loss Please, notice twice the use of the word “impedance-matched” in the previous paragraph. This is because a mismatched line will suffer additional power loss. The maximum voltage and current amplitudes on a mismatched line are proportional to the square root of the −−−−− standing-wave ratio (√ SW R ) . This increase in effective current raises the ohmic losses (I 2 R) accordingly, whereas the increase in effective voltage increases the losses in the dielectric ( ER ). 2

Typical use case From a practical point of view, suppose you happen to have a severely mismatched antenna and you chose to perform the impedance matching not at the antenna but in the shack. In such a case, it is in your interest to use a two-wire line of sufficient voltage and current rating over a coaxial cable. Not only will the loss and cost be much lower than with coax, also a voltage breakdown of the dielectric will be less likely to occur. For insanely high power levels (broadcast), four- and five-wire lines may offer a solution. Answer

by aa6yq

The primary advantages of coax with respect to ladder line are 1. most transceivers are equipped with coax connectors, whereas using ladder line requires a balun or balanced tuner 2. coax is not affected by nearby metal objects, unlike ladder line 3. the impedance of coax doesn’t change when it rains or snows, unlike ladder line The primary advantages of ladder line with respect to coax are 1. lower loss at frequencies of 28 MHz and up 2. easier to make connections 3. can drive a balanced antenna (e.g. a dipole) without a balun 4. lower weight Tags: coaxial-cable (Prev Q) (Next Q), feed-line (Prev Q) (Next Q)

Q: What is the logic behind RG cable codes Tags: coaxial-cable (Prev Q) (Next Q) What is the logic behind the names of different RG cables? The Wikipedia’s Coaxial cable page has a list of different coaxial cable standards but I cannot find the internal logic of the naming. I would assume that coding pretty much anything would be easier if you give meaning to the number, such as outer diameter or insulator material. Now the numbers seem totally random. Tags: coaxial-cable (Prev Q) (Next Q) User: oh2fxn Answer

by adam-davis

“RG” stems from old, obsolete military specifications, standing for “radio guide”, and the number is actually arbitrary. Part of the reason they are obsolete is that they weren’t specific enough - RG-6 can reasonably be assumed to have an 18 gauge solid center conductor, but beyond that the dielectric, velocity factor, or completeness of the shielding conductor aren’t always specified. Some amount of standardization exists, as shown in the wikipedia article, with additional characters after the “RG-6” type code. Whenever you see generalizations like “RG-6 has better performance than RG-59 for application X” you must ask for manufacturer and part number for the two cables, because the performance advantage might not exist with two other “RG-6” and “RG-59” cables. While we don’t necessarily need to shy away from using the generic name, be sure to specify important cable parameters whenever they matter if you are ordering or sharing project information. Otherwise you may end up with a cable that doesn’t meet your needs, or someone attempting to replicate your project or solve your problem will be unsuccessful at duplicating your setup. Tags: coaxial-cable (Prev Q) (Next Q)

Q: How to keep a disconnected coaxial connector weatherproof? Tags: coaxial-cable (Prev Q) (Next Q), safety (Prev Q) (Next Q) The advice I have seen on lightning safety is that if you don’t have high-quality lightning protection (and associated grounding) installed on your feed line, it is advisable to, during a storm and preferably whenever you are not using your station, is to disconnect the antenna feed line from your equipment and “throw it out the window”, to separate it from the interior of the house. This seems like a perfectly reasonable idea to me, except for the fact that “out the window” is likely to be wet, especially under the circumstances. How can I protect the free end of the coaxial cable (a PL-259 connector in this case) from water and other environmental damage? Permanent connections can be wrapped with amalgamating tape, but this is temporary and recurring.

It is possible I could arrange to hang the cable right under the eaves of the roof so as to avoid actual rain, but it would still be exposed to damp, windblown crud, bugs, and so on. I do have a rubber dust-cap the cable came with but it doesn’t fully enclose the connector — would that be sufficient, assuming there isn’t actually rain running down the cable? Or alternatively, what other approaches should I consider for the safety of myself and my equipment, besides the above two? Note I am in a rented space and all of my current equipment is specifically installed “temporarily”. (Taking down the antenna itself is quite easy and I would probably do it in the event of a predicted storm, but even then the feed line is still a conductor outside of the building, and partly on the roof.) Tags: coaxial-cable (Prev Q) (Next Q), safety (Prev Q) (Next Q) User: kevin-reid-ag6yo Answer

by phil-frost

I’d recommend one of two solutions: 1. Don’t throw it out the window.

Most lightning damage comes not from direct strikes but nearby strikes, which can still induce large-ish voltages on the feedline: not enough to make lightning, but enough to damage things. A couple feet of air between the feedline and the tranciever will protect against this. If you do get a direct strike, you will probably have a lot of problems, feedline out the window, or not. Sure, you are taking an additional risk, but it’s a small one, and maybe acceptable. Unless you have a very large tower, it’s probably nearly as likely that lighting will strike your home’s wiring, so unless you are unplugging that also, the additional risk of feedline-not-out-the-window is negligible. 2. Don’t throw it out the window, but ground it really well, inside.

If you can arrange for a good Earth ground, and put a connector on it, you can detach your feedline and connect it to this ground. This is as good as throwing it out the window, without the difficulties of protecting the feedline’s end from the elements. It still wouldn’t hurt to have this grounding point be physically away from your valuable equipment, where possible. Note that in this case, it’s important that the ground you use for the feedline when it’s disconnected is used only for that purpose. It exists to reduces the chances that current from a strike traveling on the feedline will arc into your house wiring, ductwork, pipes, or desk. If you were to say, connect a radio chassis to this ground, you have now created a real problem, even if you disconnect the feedline, because you haven’t actually disconnected it. Should lightning strike the power lines, or even strike somewhere close to your house, there could be hundreds or maybe thousands of volts difference between the utility ground at the electric distribution panel, and the extra one you added for the feedline. Your radio is sitting between these two points, a lot of current will flow through it, and you might be

sad. Lightning current from a strike on the antenna will likewise go through your radio, to the electric distribution panel. Bad. Answer

by adam-davis

There’s no easy way to weatherproof it, but only you can know how bad the weather is likely to get, and balance the effort and cost of providing protection against the actual needed protection. If you do want to throw it outside and protect it, though, one method that works fairly well is to take a piece of capped PVC mounted so the cap is up, forming a tube with the open end down. Mount it to the side of the house within reach of the window or access point, with a little dowel or notched section of the PVC extending from the bottom an inch or two. When you need to put it away, shove the cable end up into the PVC, then secure it on the dowel with a clip (clothespin, binder clip, etc), or rubber bands, velcro tie, etc. Taking it out is simply reversing the process. Leave the clip/velcro/etc in place so you aren’t scrounging for one when you need to deal with it next time. This isn’t meant to be weather proof, only to provide temporary short term protection for brief storage periods. If you want to store your cable end outdoors for more than a day or two, humidity, bugs, and other issues will arise that this solution isn’t meant to solve. Tags: coaxial-cable (Prev Q) (Next Q), safety (Prev Q) (Next Q)

Q: How to choose a coaxial cable Tags: coaxial-cable (Prev Q) How do you know which coaxial cable to choose for your application? For instance; I require a cable that has a 50ohm impedance, an operating frequency of 2.4GHz, length of 100mm, and needs to be semi rigid to support the elements of the antenna I am going to make. Requires a RP-SMA connector. The antenna is going to be used on a video transmitter if that is of importance What would be a suitable cable and why? Previously I have used RG316 then gained rigidity with wire strapped to the outer. Tags: coaxial-cable (Prev Q) User: ben Answer

by phil-frost

Your primary concerns are likely to contain: Characteristic impedance (Z 0 ). This is usually dictated by the other components in your system and is usually 50Ω for amateur radio applications. 75Ω components are

also not difficult to find due to their widespread application in TV. Loss. At a given frequency, a given cable will have some loss figure, usually given in units of decibels per unit length. Losses increase with frequency, so a cable that might work fine at 960 kHz wouldn’t be much more than a heater at microwave frequencies. Because loss is proportionate to length, at shorter lengths a lossier cable may be more acceptable. Power handling. Several things limit this. One is loss as above: losses become heat, and excessive heat will damage the cable. The cable must also be able to withstand the voltages associated with the power without suffering dielectric breakdown. Physical characteristics. Do you need a cable rated for direct burial? UV exposure? If you need a tight bend radius, you probably need a smaller diameter cable. Flexible or rigid? Will the cable need to withstand repeated bending from handling, or is it in a permanent installation? Will people potentially step on the cable? Compatibility with connectors can be a concern: clearly you will not be attaching an SMA connector directly to a 2-inch hardline. Fortunately, coax cables tend towards standard dimensions and thus compatibility with connectors is usually not difficult. For example, there are many cables that have the same physical dimensions as, and accept the same connectors as RG-58. Cost. The materials and manufacturing techniques used to achieve any of these desirable properties cost something. A good engineer is one that selects the cheapest solution which performs acceptably. Availability. Can you buy it at the electronics store at the corner, or must it be ordered? Is it in stock? Is it sold by the foot or by the spool? With these concerns in mind, decide which are most important for your application, then browse distributor and manufacturer catalogs until you find something acceptable. The catalog will specify a few key parameters such as loss at a couple frequencies, basic construction, cost, and size. Pick a few candidates and then read the datasheets, which specify all the parameters in much more detail. Frequently they will also contain helpful information such as compatible connectors, applications to which the cable is especially well suited, etc. Then make your choice. Tags: coaxial-cable (Prev Q)

Feed Line Skip to questions, Wiki by user dan-kd2ee Questions on topic in this tag include anything to do with the use of any type of RF feed line, coaxial or otherwise. The selection of cables and connectors; how to route, solder, and splice cables; the use of cables in outdoor and other environments; the use of leaky coaxial cable as an incidental radiator; or the building of a balun or antenna using feed line are all on topic in this tag.

Questions Q: What is the purpose of a balun and a unun in a feed line? Tags: feed-line (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q) I have never understood how a balun or a unun works and under which situation I need to use either of them in an antenna feed line. Tags: feed-line (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q) User: dinesh-cyanam Answer

by walter-underwood-k6wru

A balun matches a balanced load to an unbalanced line, but it can also do other useful things. A current balun can present a high impedance to common-mode signals, which will help reject noise. Common mode signals are the same on both conductors, so are not “balanced” or differential. An unun is an impedance transformer, usually 4:1 or 9:1, which matches an unbalanced antenna to a feedline. A 9:1 transformer is often used for an end-fed half wave antenna. This document by Jim Brown (K9YC) is long, but tremendously helpful in understanding baluns, chokes, and reducing RF noise: “A Ham’s Guide to RFI, Ferrites, Baluns, and Audio Interfacing” Tags: feed-line (Prev Q) (Next Q), antenna-construction (Prev Q) (Next Q)

Q: What happens in a low loss feed-line with a high SWR Tags: feed-line (Prev Q) I was recently reading an interesting article understanding of the SWR.

from the ARRL to get a better

The following case is still unclear: A low loss feed-line with an impedance that doesn’t match the antenna’s impedance and the receiver’s impedance. In this case a large part of the signal should “bounces” back and forth into the feed-line due to the impedance mismatch. At this point the article states that: The energy bounces back and forth inside the cable until it’s all radiated by the antenna for a lossless transmission line. An important point to realize is that with extremely low loss transmission line, no matter what the SWR, most of the power can get delivered to the antenna. I understand that during each “bounce”, due to the impedance mismatch, some amount of

energy will be transmitted and the rest reflected. I don’t understand how this transmitted power could be useful. After “bouncing” back and forth the part of the signal that will be transmitted will probably be out of phase with the signal sent by the transmitter. Even if by any luck the reflected signal and the signal currently sent by the transmitter happened to be in phase, the information conveyed wouldn’t be the same. So to me, even if almost of the power is transmitted, due to the high SWR most of this power should be just noise and don’t improve the quality of the transmission in any case. But it’s not what the article seems to explain. What did I miss ? Tags: feed-line (Prev Q) User: itchap Answer

by phil-frost

For many modulations, the modulation is very slow compared to the propagation delay of the feedline. For example, SSB is typically limited to no more than 4 kHz. That corresponds to a wavelength of of 75 km. As long as the feedline is significantly shorter than this, then the delay due to the feedline is negligible. It may be easier to understand intuitively in a digital case. For example, PSK31 sends 31.25 symbols per second. 31.25 Hz corresponds to 9600 km, meaning by the time you are sending a bit, the previous bit is 9600 km away. This breaks down for very high-speed modulations. For example, 8VSB modulation used by HDTV broadcasts transmits 10.76 million symbols per second, equivalent to a 29 meter wavelength. At these speeds, a feedline is long enough to introduce significant delay, which could come out looking like multipath distortion . Then again, TV channels are 6 MHz wide. Most amateur transmissions are several orders of magnitude narrower. Protip: don’t operate your commercial TV broadcast station with a poorly matched feedline. But for most amateur transmissions, we can consider the transmission as a pure sine wave, which is a reasonable approximation given the timescales dictated by the length of the feedline and the modulation. Then, it helps to visualize what a standing wave in the feedline looks like. From Wikipedia :

If we regard the transmitter to be on the left and the antenna to be on the right, then the blue wave represents the transmitted wave, and the red wave the reflected wave. Now here’s the thing to realize: this particular image depicts a complete standing wave on a lossless transmission line. In this case, we are delivering 0 power to the antenna, the VSWR is infinite, and the transmitter’s finals are probably about to explode. This doesn’t happen in practice because our antennas always accept at least some of the power. In practice, only some of the power is reflected back, and the result is a partial standing wave. Dan A Russel has a page of great animations , like this one:

In the case of a partial standing wave, we can see that the envelope (outlined by the dotted lines) does not reach 0 amplitude at the nodes. In this case, some power is transferred. This is also a good visualization of VSWR: it is the ratio of the voltage amplitude at the antinodes (envelope maximums) to the voltage amplitude at the nodes (envelope minimums). Notice also that the reflected wave might arrive back at the transmitter in any phase, depending on the length of the feedline and the antenna’s reflection coefficient. It may or may not be in phase, but it will be a constant phase, not just noise. By adding an antenna tuner we can reflect the reflected wave back at the antenna, and adjust the phase of this rereflected wave to be whatever we want, within the limits of the tuner’s capabilities of course. Tags: feed-line (Prev Q)

Receiver Skip to questions, Wiki by user wprecht–ab3ry A radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form, usually in the form of sounds, images or data. The technology of detecting RF energy has progressed since it was first demonstrated at the end of the 19th Century. Moving from early crystal detectors through vacuum tubes (thermistors) to solid state transistors.

Questions Q: How is the FM-signal demodulated in my receiver? Tags: receiver (Prev Q) I’ve built a radio receiver and I’m wondering how the demodulation works here. I think it’s done by T1 and T2 (I’ve used BC547 instead of BF494, they’re quite similar), but I’d like to know more about it.

Source: Tags: receiver (Prev Q) User: superlimonade Answer

by phil-frost

Essentially, it is an FM to AM converter, followed by an AM detector, followed by an audio amplifier. The heart of this circuit is C1 and L. Together, these make a parallel LC circuit . At resonance, this looks like a very high (for ideal components, infinite) impedance. Away from resonance, the impedance decreases and becomes more inductive or capacitive.

simulate this circuit

– Schematic created using CircuitLab

Our circuit will mostly be operating at or very near resonance, so the reactive part of the impedance is negligible. Instead, we can think of the parallel LC circuit as a variable resistor, the resistance of which varies with frequency. You might see where this is going: if we can design an amplifier and use this LC circuit to set the gain, then changes in frequency change the gain, and thus, the amplitude. Then we’d have an FM to AM converter. T1 and T2 form that amplifier. Specifically, they are a regenerative circuit . Regenerative circuits use positive feedback to increase gain beyond what would be possible with a single active device. They are very much like oscillators. Like oscillators , they require feedback with a 360° (or equivalently, 0°) phase shift. Unlike an oscillator, we want the gain to be less than 1 (but very close). If it’s more than 1, then we have an oscillator and we’ve actually made a transmitter.

simulate this circuit

Let’s consider what the AC signal from the antenna does to this circuit. When the antenna voltage rises, T2 turns on more, lowering its collector voltage (that’s an inversion, or a 180° phase shift). This in turn decreases the base current of T1, increasing T1’s collector voltage (another 180°). Thus, these two transistors form a positive-feedback amplifier. The gain depends on LC. Near resonance, LC is a very high impedance and gain is at a maximum. Away from resonance, LC is a lower impedance and the gain decreases. This forms an FM -> AM converter: at resonance (tuned to the center frequency of the station) amplitude is at a maximum, and as the carrier deviates away from this center, the amplitude decreases. Other stations are far enough away from resonance that the gain is very low, and they have very little effect on the circuit. From here on out it works just like an AM radio. The output of the oscillator (taken off the base of T2) can only sink current and not source it: this provides the rectification. That rectification in combination with C2 and R1 forms an envelope detector. IC1 is just an audio amplifier. And there you have it. A dead-simple, direct-conversion, regenerative FM receiver. Tags: receiver (Prev Q)

Jargon Questions Q: What do “QRM” and “QSB” refer to? Tags: jargon (Prev Q) (Next Q) An answer on Basic QSO format? those terms mean?

mentions things like “QRM” and “QSB”. What do

Tags: jargon (Prev Q) (Next Q) User: amber Answer

by amber

“QRM” is one of many Q-codes used as abbreviations in radio communication. “QRM” in particular refers to human-generated interference (as opposed to “QRN” which is used to refer to atmospheric noise). “QSB” refers to fading (variation in signal strength over time). The codes originated from the desire to keep CW (morse code) transmissions as brief as possible due to the format’s inherent bandwidth limits, but have stuck around and now often show up as abbreviations in regular conversation as well. Tags: jargon (Prev Q) (Next Q)

Q: What does Ham mean? Tags: jargon (Prev Q) (Next Q) Amateur radio operators are always referred to as Hams, it’s basically the most common term for the hobby, at least around here. Where does the term come from? I heard that it’s an acronym for something, is that true? Tags: jargon (Prev Q) (Next Q) User: dan-kd2ee Answer

by digitalcraig

The Etymology of Ham Radio Wikipedia article states that the term was originally used in a derogatory way by professional radiotelegraph operators about amateurs similar to the way an incompetent actor would be called a ham. The term was embraced by amateur radio operators and turned into a term to describe themselves. I found some other interesting explanations which the Wikipedia article calls false

etymologies: 1. Home Amateur Mechanic magazine as a popular magazine about amateur radio, but there is no evidence that the magazine ever existed. 2. Hertz-Armstrong-Marconi as the last names of several radio pioneers, but this is again debunked as Armstrong was unknown at the time the term first appeared. 3. Hammarlund was a company that made amateur radio equipment and their products became such a part of the early pioneering days of amateur radio that they were referred to as “ham products” and people who used them were “ham operators”. In reality, the company was a minor and mostly unknown company at the time the term came into use. These came from an article

by n7jy:

1. Ham was originally a derogatory term short for “ham fisted” meaning the operator couldn’t send CW very well. The term “lid” is more common today, I think. 2. Three members of the Harvard Radio Club (Alber S. Hyman, Bob Almy and Poogie Murray) called their station by their names (HYMAN-ALMY-MURRAY), but it was too long to send with CW so they eventually shortened it to HAM. When the Wireless Regulation bill, which impose regulations on amateur stations such as call signs, frequency allocations, and licensing fees, it was Hyman that testified in front of the committee considering the bill and their little HAM station became the symbol for all amateur stations at the time. (Another source: Origin of the Name “HAM” for Amateur Radio Operators ) 3. A newspaper article written in 1949 about a gathering of radio operators looking to form a club refers to them as hams with the explanation that they were so called because of “the English attempt to pronounce the word amateur”. Answer

by michael-kjörling

Originally, the term “ham” was used to describe an operator with poor skills. However, it gained usage pretty early on not only in a neutral but even positive way. The usage of the term seems to have solidified in the second half of the 1910s, as a neutral-to-positive word to describe an amateur (as in unpaid) operator. Wikipedia lists several false etymologies, including Hertz-Armstrong-Marconi station called HAM” and Hammarlund legend . Quoting from the Wikipedia article on Etymology of ham radio

, “A little


The term “ham operator” was commonly applied by 19th century landline telegraphers to an operator with poor skills.[2][3][4] (“Ham” was also in more general use as a slang word meaning “incompetent”, as in the phrases “ham handed” and “ham actor”.) as well as

But only a few months [after December 1916], in an indication of the changing use of the term among amateurs, a QST writer uses it in a clearly complimentary manner, saying that a particular 16 year old amateur operator “…is the equal of a ham gaining five years of experience by hard luck.”[7] Today, the term “ham” is used in many English-speaking countries and even some nonEnglish speaking countries to refer to amateur radio licensees. The relevant Wikipedia sources are given as: [2] Brady, Jasper Ewing (1899). Tales of the telegraph . Doubleday & McClure Co. Retrieved February 1, 2013. [3] ARRL: Ham Radio History (undated retrieval) [4] Early Radio History (undated retrieval) [7] “Who’s Who in Amateur Wireless”, QST, March 1917, p30. Tags: jargon (Prev Q) (Next Q)

Q: Why do hams often conclude messages with “73”? Tags: jargon (Prev Q) (Next Q) Looking at amateur radio forums and email threads, oftentimes amateur radio operators will use “73” or “73s” where one might otherwise expect to find “Sincerely” or “Regards”. Why? Tags: jargon (Prev Q) (Next Q) User: amber Answer

by amber

The usage of “73” for such a purpose comes from the Phillips Code , originally devised in the era of telegraphs to speed up transmission of common messages by mapping them to numbers. “73” mapped to “best regards” or “my compliments” and was intended as a general valediction for transmitted messages. It is still used for that purpose today in morse code transmissions and often makes its way into everyday correspondence among hams as a form of jargon. There is also “88” (which maps to “love and kisses”) that sometimes takes the place of “73” for communications between affectionate parties. Answer

by marcus

73 is, as Amber said, Phillips code for best regards or my compliments. I just wanted to add that it’s redundant to say 73s, which amounts to Best Regardses or My Complimentses. This puts one in mind of Smeagol, talking to Hobbitses.


by vk2cpr

Most of these things come from morse code. They were used because they have a distinctive and musical signature, listen to the rhythm of ‘73’ some time. Rhythm was (and should still be) the mark of a good operator. Alas, some non military operators in the early days were not, that is where ‘ham’ came from: because the operators sounded ‘hamfisted’. When I was a young boy my navy father taught me an exercise for learning rhythm it is: best bent wire / g Try it out some time on your morse key, you will be surprised how it improves your musicality. Tags: jargon (Prev Q) (Next Q)

Q: What is a link budget, and how do I make one? Tags: jargon (Prev Q) (Next Q) Like the question title says, what is a radio link budget? For what is it useful, and how do I make one? Tags: jargon (Prev Q) (Next Q) User: michael-kjörling Answer

by michael-kjörling

A link budget is a summary of a communications link that tries to take into account all factors which have an impact on the received signal strength. It is often used to determine the minimum amount of output power required at the transmitter for a given signal strength at the receiver, and takes into consideration power output, antenna gains, propagation losses, acceptable signal fading, and other factors (for example, for long cable runs, cable attenuation may be a factor, and at microwave frequencies, losses due to absorption in atmospheric gases become a significant factor for Earth-bound links). A few elementary values are required to make up a link budget. For unobstructed line of sight communications, which is the primary propagation mode on VHF and up, propagation losses can be estimated using the formula r L p = −22 − 20 log λ Where r is the distance covered and λ is the wavelength of the operating frequency. When the two use the same units (for example, meters), Lp comes out in dB and expresses the propagation attenuation (loss) between two isotropic antennas. For example, the propagation loss for a distance of 100 meters at 450 MHz is approximately 65.5 dB. Note that the determining factor is actually the distance in terms of wavelengths between the two antennas, so the loss goes up by 6 dB for every doubling of either the physical distance or the frequency (halving of the wavelength). No antenna is perfectly isotropic, and the common dipole has a gain of approximately 2.15 dBi (dB over isotropic) broadside to the antenna. Directional antennas generally have their gain specified as either dBi or dBd (dB over dipole, which is dBi - 2.15 dB, so 3 dBd =

5.15 dBi). To ease calculations, convert the power output of the transmitter to dBm. Using dB throughout turns many a multiplication and division into addition and subtraction, greatly simplifying calculations. For example, a 100 W transmitter puts out +50 dBm, and a 5 W transmitter puts out +37 dBm. To make the link budget, at a minimum add the transmitter output power, transmitter antenna gain in the desired direction, propagation loss and receiver antenna gain in the desired direction. By making the calculations in dB relative to some known reference (generally dBm or dBW) this comes down to addition and subtraction. As a very simple example, for a 100 W transmitter with dipoles at both ends broadside to each other (+2.15 dBi × 2), over an unobstructed 20 km path using a frequency of 150 MHz (2.00 meters wavelength), we get: +50 dBm power output + 2.15 dBi transmitter antenna gain -102 dB propagation loss, 20 km at 150 MHz + 2.15 dBi receiver antenna gain =========== -47.7 dBm signal strength at receiver

If the minimum usable signal at the receiver for the modulation and bandwidth in use, taking into account natural and receiver noise, is -90 dBm, this gives us a margin of about 42 dB, which is huge. This of course means that in theory, we can reduce our output power by a corresponding amount, maintaining communications with only +8 dBm output, as seen below: +8 dBm power output + 2.15 dBi transmitter antenna gain -102 dB propagation loss, 20 km at 150 MHz + 2.15 dBi receiver antenna gain =========== -89.7 dBm signal strength at receiver

Admittedly, the above link budget gives us for all intents and purposes no margin: to maintain communications over this path using this equipment and mode of transmission, everything must work out absolutely perfectly. To have a 10 dB margin for issues such as fading, we’d need to use +18 dBm (slightly less than 100 mW = +20 dBm) power output, which is trivially achievable with practically any handheld radio. A link budget for a HF link, or an obstructed VHF link, is much more complex because the propagation losses are harder to calculate than for a pure line-of-sight link, but the general principle remains exactly the same. A complete link budget for a line-of-sight link will at least include the following factors: + Transmitter output power - Attenuation in the transmitter’s antenna cabling, including any impedance matching network + Transmitter antenna gain in the direction of the receiver - Propagation loss in free space - Attenuation due to absorption in atmospheric gases - Margin for attenuation due to rain - Margin for attenuation in tree foilage

- Margin for attenuation due to reflection against walls etc. - Margin for signal fading + Receiver antenna gain in the direction of the transmitter - Attenuation in the receiver’s antenna cabling, including any impedance matching network = Signal strength at the receiver input terminals, to be compared with the minimum necessary signal strength It is important to note that several of these factors (propagation loss, atmospheric absorption, foilage losses, and so on) are heavily dependent on the operating frequency. This means that a link budget for one frequency is unlikely to be applicable at another frequency, even if nothing else changes. Answer That’s

by phil-karn a pretty good answer but I can add some more details.

The exact formula for path loss is 20 × log10 (4 × π ×

d ) λ

20 × log10 (4 × π) ≈ 21.98 , and that’s where the ‘22’ comes from. If your receiver specs give a minimum signal strength, then the analysis above is pretty much all you need. But in a more general link budget you have to compute the required receive power yourself from the data rate, the type of modulation and coding, and the receiver system noise temperature. The most power-efficient modulation/coding method in use is rate 1/6 turbo coding over BPSK (binary phase shift keying). This is a very popular deep space signal; it’s being used by New Horizons at Pluto, for example. This particular signal requires a minimum E b/N 0 of about 0 dB. What is E b/N 0 ? It’s the received energy per bit divided by the received noise power spectral density in watts/Hz. This also has units of energy, so the ratio is dimensionless. It’s usually expressed in decibels. The famous Shannon Limit says it’s impossible to make a system operate error-free at an E b/N 0 below -1.6 dB even if you can use infinite bandwidth. So you can see that we’re pretty close to the theoretical limit. Then you add the data rate, also expressed in decibels (with respect to 1 bps). For example, 1000 b/s would be 30 dB(bps), so your New Horizons signal would require a P /N 0 of at least 0 + 30 = +30 dB, where P is received power. That just leaves us with N 0 . In space communications, noise is usually expressed as a temperature T since everything above absolute zero generates thermal noise. The big 70m dish at the NASA Deep Space Network sites has a noise temperature of 17.5 kelvins (I looked it up). To get N0, you multiply T by Boltzmann’s constant, 1.38e-23 J/K or -228.6 dBW/Hz-K. So 17.5K is an N 0 of -216.2 dBW/Hz (or dBJ, same units). Now you have what you need to compute P, the required receive power. It is simply -216.2

dBW/Hz + 30 dB-Hz = -186.2 dBW or -156.2 dBm. That’s not much, but it’s still hard to generate all the way from Pluto! Tags: jargon (Prev Q) (Next Q)

Q: What do the three-letter modulation codes (emission designators) stand for? Tags: jargon (Prev Q) (Next Q) I’ve seen these weird three-letter modulation codes like J3E, A3F, A1A, F3E and so on. Someone even wrote 2K40J3E or 12K5F3E. What do these codes stand for? Tags: jargon (Prev Q) (Next Q) User: michael-kjörling Answer

by michael-kjörling

The emission type specifier is made up of several fields, which are defined as follows. First comes an (optional) specifier of the necessary radio bandwidth. This is four characters, mixed letters and numbers, with one of H (Hz), K (kHz), M (MHz) or G (GHz) where the decimal point would be. For example, 400H specifies a bandwidth of 400 Hz, 2K40 specifies 2.40 kHz, 25K0 specifies 25.0 kHz and 6M00 specifies 6.00 MHz. This is the bandwidth used by the signal on the air, not the modulation bandwidth. For example, narrow-band FM modulated with a 3 kHz signal would be 12K5 because it needs 12.5 kHz of bandwidth on the air. This is followed by three characters which specify, in turn, the modulation type, the nature of the modulating signal, and the type of information carried. Modulation type A = amplitude modulation, two sidebands, full carrier B = amplitude modulation, independent sidebands C = amplitude modulation, vestigial sideband D = amplitude and angle modulation of carrier F = angle-modulated, straight frequency modulation G = angle-modulated, phase modulation H = amplitude modulation, single sideband, full carrier J = amplitude modulation, single sideband, suppressed carrier K = pulse, amplitude modulation L = pulse, width modulation M = pulse, with phase or position modulation N = No modulation at all P = pulse, no modulation Q = pulse, with carrier angle-modulated during pulse R = amplitude modulation, single sideband, reduced or controlled carrier

W = pulse, two or more modulation modes used X = all other cases

Nature of the modulating signal 0 = No modulating signal 1 = Digital modulating signal, on/off or quantified with no further modulation 2 = Digital modulating signal with modulation 3 = A single analog channel 7 = Two or more digital channels 8 = Two or more analog channels 9 = Composite modulating signal, one or more analog channels plus one or more

digital channels X = all other cases Type of information carried by the modulating signal A = aural telegraphy, for people (generally Morse code) B = telegraphy for machine copying (generally RTTY or high-speed Morse code) C = analog fax D = data, telemetry, telecommand E = telephony, voice or sound F = video or television N = no information carried W = a combination of the above X = all other cases

This can be followed by two more characters giving details, which normally are not used for amateur radio purposes. Examples J3E amplitude modulation, single sideband, suppressed carrier a single analog channel telephony, voice or sound Also known as single-sideband transmissions or SSB, generally in amateur applications with voice modulation. 2K40J3E is J3E with a 2.40 kHz radio signal bandwidth. A3F amplitude modulation, two sidebands, full carrier a single analog channel video or television A1A

amplitude modulation, two sidebands, full carrier digital modulating signal, on/off or quantified with no further modulation aural telegraphy, for people Also known as Morse code and informally CW. Actual CW (pure carrier) is N0N. F3E angle-modulated, straight frequency modulation a single analog channel telephony, voice or sound Also known as frequency modulation or FM, generally in amateur applications with voice modulation. 12K5F3E is F3E with a 12.5 kHz radio signal bandwidth. Tags: jargon (Prev Q) (Next Q)

Q: What is a shallow/deep QSB? Tags: jargon (Prev Q) Probably all amateurs recognize QSB as the q-code

to represent ‘fading’.

I recently encountered the terms Shallow QSB Deep QSB A quick google search failed to yield fruit; What do the above terms mean? Tags: jargon (Prev Q) User: vu2nhw Answer

by oh7lzb

Deepness of QSB refers to the magnitude of fading. A very deep fade-out can make the received signal so weak that it becomes unreadable. A shallow fade-out would be one where the signal level drops only slightly, not affecting readability. Radio propagation conditions often change quite quickly over time. For example, QSB might start in the middle of a longer QSO, being quite shallow in the beginning. It’d be noticeable on the signal meter. On FM you’d hear a little noise on top of the carrier from time to time, on SSB the audible volume of the received signal would go down temporarily. If conditions would continue to go worse, the QSB could soon become too deep for successful communications - you would start to miss words, then whole sentences. shallow: of little depth

Tags: jargon (Prev Q)

Uhf Questions Q: Direction finding: How to find a stuck FM transmitter on 70cm? Tags: uhf (Prev Q) There’s a blank carrier on a 433 MHz FM voice frequency here. How should we go on about finding the transmitter’s location? Practical procedure? Could be somewhere downtown. Tags: uhf (Prev Q) User: oh7lzb Answer

by pearsonartphoto

The best way is to get a high gain antenna, and figure out what direction it’s coming from. Do this from 2-3 points. Take a map, and draw lines from each of the point of origins from the direction you heard the signal the strongest. That should give you at least an idea of where the signal is coming from. Once you have a rough idea, the next step is to go to said area, and repeat the process. You should be able to get a better idea of where the signal is coming from. Eventually, you’re going to be unable to pick up the transmitter, as you will get high signal anywhere you point your antenna. The next step would require an attenuator, or even just using a rubber duck antenna and using your body as a shield. FYI, this is essentially the same thing as a fox hunt, except for a less cooperative subject, and you don’t have to find the transmitter exactly. Tags: uhf (Prev Q)

Rtl Sdr Questions Q: SDR - FM Radio station interference Tags: rtl-sdr (Prev Q) I want to learn about software defined radio and how wireless transmission work in general. So I started messing around with SDRSharp and a little antenna I bought. I figured I would start looking at known frequencies like local radio stations. Some I can get to come in clear by messing with the digital noise reduction but this station (one of the strongest in my area) has a ton of background noise that I can’t seem to filter. Any ideas?

Tags: rtl-sdr (Prev Q) User: anthony-russell Answer

by juancho

The interfering harmonics are spaced at around 15.5 kHz. Do you have an old (CRT) TV set nearby? That may be the source, since TV line frequency is 15.625 Hz. If not, look for other interfering electronics, such as compact fluorescent lights or other

switched-mode power supplies (your own PC?). Tags: rtl-sdr (Prev Q)

Equipment Design Questions Q: How is the IF for a superhet selected? Tags: equipment-design (Prev Q) (Next Q) There seem to be almost as many choices for the intermediate frequency (IF) as there are superheterodyne receivers and transceivers out there. The ones I have come across are 455 kHz, 452 kHz, 1.6 MHz and 6 MHz. What would be the rationale for choosing a particular IF for a superhet? Tags: equipment-design (Prev Q) (Next Q) User: vu2nhw Answer

by wprecht–ab3ry

The short answer is that these are “standard” frequencies set aside for IF use and are reasonable free from interference. The longer answer follows if you are interested in the why. The choice of an IF frequency is one of those design tradeoffs. The lower the IF frequency used, the easier it is to achieve a narrow bandwidth to obtain good selectivity in the receiver and the greater the IF stage gain. On the other hand, the higher the IF, the further removed the image frequency is from the signal frequency and hence the better the image rejection. One problem of the problems of a superheterodyne receiver, is its ability to pick up a second or image frequency that is twice the intermediate frequency away from the signal frequency. For example, if we have a signal frequency of 1 MHz which is mixed with an IF of 455kHz. A second or image signal, with a frequency equal to 1 MHz plus (2 x 455) kHz or 1.910 MHz, can also mix with the 1.455 MHz to produce the 455 kHz. The choice of IF is also affected by the selectivity of the RF end of the receiver. If the receiver has a number of RF stages, it is better able to reject an image signal close to the signal frequency and hence a lower IF channel can be tolerated. This is why modern rigs have 2 or even 3 IF stages. The chosen IF frequency should be free from radio interference. Standard intermediate frequencies have been established and these are kept dear of signal channel allocation. As you have noted, 455KHz is a common IF. This is because broadcasters settled on this as a standard frequency during the broadcast AM days.

From a design point of view 455KHz it leads to poor image response when used above 10 MHz. One commonly used IF for shortwave receivers is 1.600 MHz and this gives a much improved image response for the HF spectrum. Ham band SSB HF transceivers have commonly used 9 MHz as a receiver intermediate frequency This frequency is a little high for ordinary tuned circuits to achieve the narrow bandwidth needed in speech communication, however, when used with ceramic crystal filter networks it leads to good results. Some recent amateur transceivers use intermediate frequencies slightly below 9 MHz. A frequency of 8.830 MHz can be found in various Kenwood transceivers and a frequency of 8.987.5 MHz in some Yaesu transceivers. This change could possibly be to avoid the second harmonic of the IF falling too near the edge of the 17m WARC band. Tags: equipment-design (Prev Q) (Next Q)

Q: Does the waveform of the VFO necessarily have to be sinusoidal? Tags: equipment-design (Prev Q), oscillator (Prev Q) (Next Q) Looking around for a VFO online, I see most kits/manufacturers make it a point to mention the waveform. Sinusoidal is a fundamental shape, whereas others (sawtooth, square) are a composite. I recall reading online (can’t remember where it was) that a VFO with a composite waveform is actually better than one with a pure sinusoid. Does the VFO signal necessarily have to be a sinusoid? Does the remark about a VFO with a composite signal ring true? Tags: equipment-design (Prev Q), oscillator (Prev Q) (Next Q) User: vu2nhw Answer

by phil-frost

Does the VFO signal necessarily have to be a sinusoid? Absolutely not. For each frequency component on a mixer’s inputs, it produces at the output the sum and difference of those frequency components. Of course, if one of the inputs is sinusoidal, then it has just one frequency component. However, if there are more frequency components it still works. Does the remark about a VFO with a composite signal ring true? Sure. Joseph Fourier proved that any periodic function can be decomposed into a (possibly infinite) number of sinusoidal components, each with some amplitude and phase. For example, a square wave

consists of some fundamental frequency, plus all its odd

harmonics. A sawtooth wave has even and odd harmonics. Each of these harmonics will generate mixing products, just as if you fed in a sine wave at that harmonic frequency. This can be used to an advantage in some designs, as long as the filtering is such that the mixing products from the other harmonics don’t cause issues. Answer

by jcoppens

A small extra bit of information… Even though many VFO circuit descriptions, as you say, make it a point mentioning the ‘cleanliness’, by far most mixer circuits then proceed to convert the sine wave into something horrible :) Mixers, in order to function as such, must be non-linear. Ideally, they should multiply both input signals, and produce neat sum and difference frequencies. In practice however, most mixers only approximate that behavior. An extreme example, is the digital mixer which just inverts the input signal (using analog switches) at the pace of a digital signal (the VFO). As Phil told you, many harmonics are present, so it’s up to the designer to include the necessary tricks to avoid those extra frequencies having a bad effect. More important than the harmonic content of the VFO, is something more difficult to measure. As most analog sine oscillators use amplifiers (transistors or integrated circuits) to oscillate, thermal effects in those semiconductors introduce modulation onto the carrier frequency. This makes the VFO not generate one clear sine, but rather an AM and FM modulated one. Depending on many factors, the Q factor of the resonator being probably the most important one, this noise can cause much more problems than harmonics. Tags: equipment-design (Prev Q), oscillator (Prev Q) (Next Q)

Safety Questions Q: How can I protect equipment against a lightning strike? Tags: safety (Prev Q) A lot of aerials (almost by design) would be rather good attractors of lightning. What steps do I need to take in the field to keep my gear safe against a lightning strike? I’m presuming the obvious already here (such as not operating in a storm), but are there any additional steps I should take? Tags: safety (Prev Q) User: berry120 Answer

by joseph

Many companies make lightning surge protectors. the install in the coax to your radio and divert the strike to ground. NOTE: THERE IS NO SURE WAY TO PROTECT YOUR RADIO EXCEPT DISCONNECTING IT FROM POWER AND THE ANTENNA. Search for polyphaser, they are well respected, MFJ also makes some lower cost options.. Answer

by kenneth-larsen

QST magazine printed a comprehensive three part article in 2002 addressing lighting. Lightning Protection for the Amateur Radio Station: QST June 2002, pp. 56-59 QST July 2002, pp. 48-52 QST August 2002, pp. 53-55 The surest way to protect your radio gear is to disconnect it from power, from the antenna, from your computer and even from ground. And even that is no guarantee — a while back I had an enormous charge of lightening struck my backyard. I had three transceivers; one rig was still connected to my computer and both the computer and rig were smoldering. The other two rigs were also fried despite being disconnected from power and antenna. My presumption is that the magnetic and electrical charges from the lightening were powerful enough to resonate and over load components in the rigs. It’s a hassle, but disconnect your rigs from power, antenna and computer. Answer

by vu2nhw

A discharge tube would serve to protect your rig from a close strike. Apart from that, make sure you have a decent ground for your shack. Having said that, it’s probably not a good idea to operate in heavy weather. Unless absolutely necessary to continue operation, I’d go QRT, and disconnect the coax from the rig. Tags: safety (Prev Q)

Emergency Skip to questions, Wiki by user dan-kd2ee This tag is for questions about the use of amateur radio in support of public safety or disaster relief in a declared emergency, including any equipment, protocols, or techniques that are specifically applicable to emergency communications. This tag is not for general questions about the National Traffic System or nets in general, or about equipment that could be used for emergency communications, unless the question is specifically about that equipment’s use in an emergency. Also on topic is the use of amateur radio for personal safety to report an emergency, such as wilderness or maritime use. General questions about radios suitable for marine installation or HF radios for portable use are not applicable, only the use of those radios to report an emergency. Questions about rules and regulations or about organizations that amateur radio operators work with in a time of emergency are also welcome.

Questions Q: How is ARES different from RACES? Tags: emergency (Prev Q) Just what the title states. Here, in India, in the context of public service we hear of RACES (Radio Amateur Civil Emergency Service). I recently learnt about something called ARES in a similar context applicable to CONUS. Yet RACES, as far as I’m aware, was relevant to the US too. How is ARES different from RACES? Tags: emergency (Prev Q) User: vu2nhw Answer

by amber

The ARRL actually has an FAQ that discusses this topic explicitly: ARES is activated before, during and after an emergency. Generally, ARES handles all emergency messages, including those between government emergency management officials. RACES, on the other hand, almost never starts before an emergency and is active only during the emergency and during the immediate aftermath if government emergency management offices need communications support. RACES is normally shut down shortly after the emergency has cleared. The FAQ continues into more detail, but the general gist is that RACES is specifically for coordinating actual civil services, whereas ARES is a more general communications network for overall messaging around emergencies. Answer

by pete-nu9w

In addition to what @Amber said, in the US RACES is only activated by order of the President of the United States. When that happens, all other amateur services (including ARES) are shut down. So many ARES organizations encourage their members to also join RACES, so that they can just change hats and continue to operate when RACES is activated. Tags: emergency (Prev Q)

Repeater Skip to questions, Wiki by user kf5rrr Repeaters are usually used to boost the range of transmitters. For example, the range of a 5W hand held can be greatly increased. Repeaters designed for duplex operations have different transmit and receive frequency. The repeaters also have to be keyed on by sending certain tone frequency - or a sequence of tones.

Questions Q: How to access a P25 repeater? Tags: repeater (Prev Q) Are there any special instructions for accessing a P25 repeater? What makes it different from a CTCSS/PL-tone-encoded repeater? What special features does a radio need to access it? Tags: repeater (Prev Q) User: dan Answer

by wprecht–ab3ry

P25 is a suite of standards for digital radio communications. P25 is intended to facilitate interoperability between different public safety agencies during emergencies and/or joint operations. Note that this is a North American standard (and a few other places), Europe has a similar but imcompatible standard called TETRA. A radio needs to be specially designed for P25 use. The public safety agencies use reallocated TV frequencies in the 700MHz range. Most of the usual suspects make HTs for P25 and a couple make dual band radios for amateur use. Due to the audio quality and extra features, some amateur clubs are setting up P25 repeaters usually on the 70cm band, but some on the 2m band. P25 repeaters use whats called a NAC (Network Access Code) in place of the PL tone/CTCSS access common to amateur repeaters. This a 12-bit prefix that is attached to every packet (including the digitized voice packets). 12 bits means 4096 possible access codes, quite a lot more room than the previous analog methods. There are a few special codes, a default and an “open” code that will pass all traffic. To program a radio, you need to use a computer, it’s too complex to allow keypad programming. The commerical / public safety versions also support encryption using DES, triple-DES, and AES though it’s not consider all that secure do to implementation flaws. However, it’s good enough to meet privacy concerns for first responders. Tags: repeater (Prev Q)

Frequency Questions Q: How can you calculate the frequencies for each band? Tags: frequency (Prev Q) I’ve just started studying for my HAM license a couple of weeks ago, so please excuse me if this is a remedial question… I have the Canadian Amateur Radio Basic Qualification Study Guide (which I’m finding is terribly hard to understand). Their explanations of just about everything appear to be missing pertinent information that allow the reader to connect the dots and consequently I’m struggling to understand what they’re explaining… anyway, the book discusses a formula which supposedly allows you to determine the bond between frequencies and their band - i.e. the calculation in the book tells me that 300 / Wavelength = Frequency… where one is to assume that 300 is a rough simile of the speed of light in millions of meters per second. The book suggests the resultant frequency is approximately (within some unexplained tolerance) the middle of the bandwidth for that band plan. I’m noticing that using this formula for many bands the resulting frequency doesn’t fall within the suggested frequency range for that plan and where they do, many don’t fall within any discernible tolerance of the middle. For example: 20m band = 300 / 20 = 15.000 MHz, whereas the book suggests the frequency band falls between 14.000 - 14.350 MHz. (Clearly 15.000 MHz falls outside that range) 2m band = 300 / 2 = 150.000 MHz, whereas the book suggests the frequency band falls between 144.000 - 148.000 MHz. 33cm band = 300 / 0.33m = 909.091 MHz, a long way from the middle of the suggested frequency band of 902.000 - 928.000 MHz Even if I substitute the more accurate (according to Google) measurement of c being 299,792,458 m/s, I arrive at 14.990 MHz for 20m, still not within the frequency band. Clearly I’m missing something, can someone explain what I’m not understanding? Tags: frequency (Prev Q) User: benalabaster Answer

by kevin-reid-ag6yo c = wavelength frequency c

= frequency

c = frequency wavelength The above relation is a fact of physics. It’s true unconditionally (provided you are using consistent units, e.g. wavelength in meters and c in meters per second); it’s how you convert between two different ways of measuring a wave. The frequency limits, and names, of the bands are not physics; they were invented by humans. The frequency limits are a matter of the regulations that divide up the radio spectrum among many users. The limits of the amateur bands are semi-arbitrary. The common names for the bands (“20 m”, “2 m”, and so on) are simply the closest round number to the actual wavelengths. (In your example of 33 cm, note that 32 and 34 cm would be outside the band entirely. 33 is the best two-digit approximation.) What your book should have told you is not that you can use the above relation to find the limits of the band, but that given that you already know the bands and frequencies, you can use it to find which band a frequency belongs to, or vice versa, because while the band names do not always fall in the frequency limits, the correct band/frequency will always be the closest match. For example, 300/143 ≈ 2.098 , so we can conclude that 143 MHz is in the 2 m band if it is in an amateur band at all, which it isn’t (but e.g. 145 MHz is). If you wish to know the limits of bands, you must memorize them; there are no shortcuts. The relationship between wavelength and frequency can, however, be used to match up those limits to the wavelength-names of the bands. Tags: frequency (Prev Q)

Antenna Construction Questions Q: Is an antenna analyzer necessary for building antennas? Tags: antenna-construction (Prev Q) I’d like to try my hand at building a few antennas for VHF/UHF use. I’m going to be going approximately from established designs, but obviously the final result will require some tuning. I don’t currently own either an SWR meter or antenna analyzer. Is an SWR meter good enough for what I want to do, or will an antenna analyzer be necessary for this? What are the benefits of an antenna analyzer in such situations? Tags: antenna-construction (Prev Q) User: david-kf4mdv Answer

by kevin-reid-ag6yo

I’ve not personally built antennas from scratch, but I appreciate my antenna analyzer just for being a good instrument — making the invisible aspects of my antenna system visible. Compared to using a SWR meter for the purpose, an antenna analyzer: Displays more information. A SWR meter still gives you enough information, in the sense that you can try things until they move towards 1:1 SWR, but it’s a one-dimensional measurement: if you tried to adjust an antenna using it you’re doing a “hotter colder” search, trying things until it improves. An antenna analyzer will tell you resistance and reactance independently, which allows you to more directly understand the problem. For example, you can have an exactly resonant antenna, which simply has the wrong magnitude of impedance (you need an impedance transformer). On a SWR meter this can show up as the SWR having a minimum point but remaining well above 1:1. (That minimum point is not necessarily the resonant point .) On an antenna analyzer, you can immediately see that you’ve got R = 34 Ω instead of 50 Ω (or whatever), and build that correction into your balun. High-end antenna analyzers can also give you measurements at multiple frequencies — either as a graph or individual readings at selected frequencies. A graph allows you to easily obtain measurements in the opposite direction — not “how suitable is this antenna at this frequency?”, but “what frequencies is this antenna good for?”, as well as other RF-electronics measurements like finding the resonant frequency of a circuit or the upper frequency limit of a ferrite choke.

In the above picture: my RigExpert AA-600 antenna analyzer displaying an impedance graph (it can also compute SWR from the same data). You can see directly from this graph that whatever it’s connected to is resonant at the frequency at the middle of the graph (reactance crosses zero) and at that point has a resistance (and also magnitude of impedance) of 100 Ω. Lets you use less transmitted power. To measure the impedance of your antenna, no matter what instrument you use, you need a signal generator — a transmitter — somewhere. An antenna analyzer has a low-power signal generator built in. If you use a SWR meter, you have to use a separate one; if you use your regular transceiver for the purpose, you’re limited to its lowest power setting, which might be a few watts! Even if you have a lower power transmitter, it might not be sufficient to show a reading on the SWR meter, which has scales for much higher power levels. By comparison, my antenna analyzer’s output falls within FCC Part 15 emissions limits, so I’m much less likely to interfere with anyone else (and don’t have to stop to identify myself, either). Answer

by k7peh

I couldn’t live without my two antenna analyzers — I may even get a VNA (vector network analyzer) although that is not necessary for simple antenna analysis. I own both the MFJ 259B and the Autek Research RX Vector Analyst VA1. Although both do roughly the same thing, they have a few different features and I will touch on a few of those. Besides digital readout, the MFJ 259B also has an analog SWR meter which greatly helps in finding resonant spots on an antenna using a frequency sweep. You can watch if you are getting close or drifting away much easier than with digital readout. You can measure capacitance and inductance with both but the MFJ259B does not give

you the sign of the reactance. That is, negative for capacitance and positive for inductance. You can determine the sign merely by doing a small shift in frequency and seeing which direction the reactance swings (lower for capacitance if frequency shifts upward for example). The Autek VA1 though includes the arithmetic sign of reactance so it is just slightly easier if you want a capacitance versus inductance readout. So, whether you are building antennas for resonance or cutting transmission line to be a transformer, the use of either of these two analyzers makes it gut simple. Postscript: I forgot to mention whether an SWR meter is any good? Well, it can tell you when you are really bad but it does not really help enough in my opinion. After all, a 50ohm resistant dummy load gives an SWR of 1:1 but that does not say it is a good antenna. Also, by knowing the R and X values of the reactance, you are able to determine where problems might lie with an antenna. Remember that resonance is where it is purely resistive so X = 0 or close to zero. Answer

by phil-frost

An antenna analyzer is not necessary. Sure, it’s handy. A VNA is even handier. But then, these things could set you back maybe $100 if you go for the cheapest antenna analyzer, or maybe thousands of dollars if you go for a modern VNA. If you just want to know if you need to trim a bit off a wire dipole or not, and simply get on the air without toasting your transmitter, none of these things are necessary. While there’s a certain joy in being able to measure and quantify exactly how things are operating and make it all “just so”, radios are in fact quite forgiving. An AC current wants to radiate. In fact, there’s an entire industry around making things not radiate . If you wonder how to make an antenna without these tools, you need only look to the recent past. It wasn’t that long ago that we did not have solid state electronics, and test equipment like we have today was either very expensive, or nonexistent. Most of the methods used in those days to measure antenna impedance involve putting an antenna in some kind of bridge and comparing it against a known impedance. Here’s one example of a dead-simple approach:

You can read the full question for an explanation of how it works. It’s not particularly sophisticated, but if you just need to trim your antenna until it’s not a horrible match to 50 ohms, it will work just fine. If you have an SWR meter, you can also just adjust for minimum SWR and accomplish the same thing. Note you don’t need the matching section (L1, L2, and C3) if you just want to measure impedance. If you want to take the sophistication up a notch, you can use a grid dip meter . You can find them at any hamfest, or used on eBay or whatnot for some tens of dollars. Just a few decades ago, these were state of the art antenna test equipment. The physical laws that govern their operation have not changed, and they work as just well today. As another step up, you can consider any number of used impedance bridges which are similar in concept to the schematic above, but have adjustable and calibrated inductors and capacitors so you can measure the complex impedance of the antenna. This is in effect what an antenna analyzer does, the only difference being that the antenna analyzer will automatically adjust the knobs for you, and maybe measure impedance at a range of frequencies at a push of button. Tags: antenna-construction (Prev Q)

Satellites Skip to questions, Wiki by user michael-kjörling This tag covers all amateur radio communications with man-made Earth-orbiting objects, including communication over dedicated amateur radio satellites (AMSATs) and with astronauts aboard a space station such as the International Space Station (ISS). It does not cover reflecting signals off passive, natural objects such as Earth-Moon-Earth communications (EME) or meteor scatter.

Questions Q: What is spin fading in satellite signals? Tags: satellites (Prev Q) Why do signals from satellites experience “spin fading” as the satellite rotates? What are the effects that spin fading has on a radio signal? From test question: T8B09 Tags: satellites (Prev Q) User: jc-hulce Answer

by paul

Take the simplest case of a VHF dipole receiving antenna on board a spin stabilized satellite. –––—O––––- Here is the satellite now. Skip code block \ \ \ \ \ O and here is is a bit later \ \ \ \ \

As the satellite spins, the dipole rotates, and the resulting polarization of the dipole also rotates. For instance it may go from horizontal polarization to vertical and back again. If you transmit to the satellite with a horizontal or vertical polarized yagi, your transmit yagi will sometimes have the same polarization as the receive at the satellite and sometimes it will not. When the polarizations are different there can be cross polarization loss of up to 20-30db. This is the phenomena behind spin fading. It can be corrected by using circular polarization at the transmitting or receiving location or both. The loss of a linear polarization antenna from/to a circular one is about a constant 3db over the case where both of the antennas are circular polarized, and because it is constant it is not affected by spin. If you have a couple of loose polarized sunglass lenses, you can place them against each other and rotate one of them while keeping the other stationary, you will see a similar effect with the variable attenuation of light travelling through the pair of lenses. Tags: satellites (Prev Q)

Grounding Questions Q: When is RF grounding necessary, and when is it not? Tags: grounding (Prev Q) (Next Q) I’ve seen many installations, particularly at field day and also in second-floor installations, where RF grounding is ignored entirely. What are the drawbacks to this and when is it absolutely essential to have RF grounding? Tags: grounding (Prev Q) (Next Q) User: bill–k5wl Answer

by andrew-beals

Two drawbacks to ignoring your grounding: 1. You will have a poor(er) signal. 2. You could become the ground and experience an RF burn first-hand. That said, VHF antennas are often not grounded - handhelds and VHF radios in cars, for example. Tags: grounding (Prev Q) (Next Q)

Q: What causes ground losses in a HF antenna system? Tags: grounding (Prev Q) This applies to mobile and fixed installations. What are ground losses, and how can they be minimized? It seems to involve proximity to the ground, but what is the mechanism that causes loss? Does antenna installation height influence ground loss in any way? Tags: grounding (Prev Q) User: bill–k5wl Answer

by phil-frost

To add to what Dan is saying, for (horizontal) dipole antennas, ground height is important because although a dipole doesn’t require ground to work, ground is still a (lossy) conductive plane, and you still get an image . That is, it appears that there’s another dipole, fed in anti-phase, underground. Even if nothing in your transmitter or antenna is connected to the ground, your antenna will be capacitively coupled to the ground. There is

no avoiding it. If the dipole is close to the ground, then the currents in the ground can be quite strong, incurring significant resistive losses along the way. You could put radials (or any conductive mesh, really) in the ground to mitigate this. But also: this image makes your dipole a kind of phased array . Depending on the spacing of the antenna and it’s image, this might make a phased array that helpfully directs most of the RF energy at the horizon (low takeoff angle, desirable for HF DX exploiting skywave propagation), or unhelpfully straight up (useless, unless you are trying to exploit NVIS propagation on communicate with something in space). Radio Antenna Engineering has a more detailed explanation

, and this:

One interesting thing to note about this image: you can’t get maximum gain in any direction until the dipole is 0.25λ high. Remember, the image is twice this distance away, and anti-phase. Below this height, in any direction you will get at least partial phasecancellation. At h = 0.25λ , you have two antennas, in anti-phase, 0.5λ apart, which makes

the add instead of cancel, but only if you are directly over the antenna, which isn’t useful for skywave propagation. Thus, the general recommendation to get a dipole something like 0.5λ high, which sends most of the energy at a reasonably low take-off angle, making the best of the transmit power available. Answer

by dan-kd2ee

While ground effects are common concerns in almost every antenna and radio system, they are particularly important in the case of a monopole antenna. Monopole antennas, including quarter wave verticals along with many other electrically short verticals, are different from dipoles because the currents going into the elements do not balance. While a dipole has equal but opposite currents at all times, a monopole can’t. One half of the signal goes into the antenna, and the other half has to come back through the shield of the coax, which is connected to ground. When we’re talking about antenna modeling, we describe the ground plane as an image plane - everything above it is mirrored below it. So in theory, the monopole should act as though there was another monopole directly below it, being fed 180 degrees out of phase. We do see the correct amount of current returning through the ground path for this model to work - we do have equal but opposite currents - but while your antenna is lowresistance wire and most of that current is being radiated, the ground typically has somewhat higher resistance. It’s impossible to set a value here, because it is dependent on soil type, weather, how deep the water table is, and other factors, but it is greater than that of your antenna. Because of this resistance in the ground, some of the power coming from your radio will be lost to normal resistive heating. Since, at a constant power and given P = V I = I 2 R the increased resistance in the ground results in decreased current into the ground (at constant power). Since the antenna and ground currents must be equal but opposite, that also decreases the current flowing into your antenna and therefore your actual radiated power. You also can’t just stick a multimeter into the ground to find this resistance - it’s the resistance from your antenna feed point to the point where the coax shield is grounded, but it is frequency dependent because there is a capacitive component as well. An antenna analyzer can be used to detect the total resistance (including radiation resistance of the antenna) and this can be compared to a model with an ideal ground (perhaps obtained from EZNEC or another modelling program) to get the “extra” real-world losses, including ground loss. This also explains why height factors in: Your antenna system is effectively a series resistance (from ground loss and other factors), capacitance (between antenna and ground and other effects), and inductance (from loading coils and other effects). If the antenna is mounted further from ground, the capacitance decreases, and so the ground loss becomes a greater part of this total reactance, which is why it is better to have your antenna near to a ground and to have a ground that is as low resistance as possible. An extra way to help this is to install radials - wires underground at about a quarter wavelength which would act as a lower-resistance path for the return current to take.

Tags: grounding (Prev Q)

Phone Skip to questions, Wiki by user user322 This tag is for any questions about analog voice modes, including what bands are allocated for phone use, what modes qualify as phone, how the different modulation schemes compare, and how to make a QSO on a phone mode.

Questions Q: Is use of the phonetic alphabet mandatory? Tags: phone (Prev Q) The phonetic alphabet is often used on amateur radio to spell out names and callsigns more clearly, especially when the clarity may be poorer. However, there are cases where I simply forget certain parts of this - in this case, is it ok just to use any old word in its place, or would this just lead to confusion? Tags: phone (Prev Q) User: berry120 Answer

by andrew-beals

Part 97, section 119 covers this. “Use of a phonetic alphabet as an aid for correct station identification is encouraged”. Most everyone has settled on the NATO phonetic alphabet, even though its elements have varying numbers of syllables (one to three!) and aren’t comprised exclusively of trochees . To put this another way, if you make it difficult for another station to understand you, they’re not likely to want to speak to you. Answer

by evan-fosmark

It’s not uncommon to use other words in place of the standard NATO Phonetic Alphabet . For example, my callsign is K7FOS, and I typically say Kilo Seven Foxtrot Ocean Sugar after saying the NATO style because it can often be easier to interpret “Sugar” over “Sierra”. Use whatever works in order to get your message over the air effectively. Answer

by andrew-m0yma

The TL;DR; answer is No. The slightly longer answer is still No! - and listening to any pile-up will show it is not the case. As an example, QRN, QRM and QSB are often referred to as “Q R Nancy, Q R Mexico and Q S Baltimore respectively (not November, Mike and Sierra)… The point of any “code” is to make sure the recipient understands the transmission… and the advantage of the NATO Standard Phonetic Alphabet is that most (if not all) operators (should) know the letters, which is especially important when dealing with non-English native-speakers. Tags: phone (Prev Q)

Math Skip to questions, Wiki by user user322 Some example questions in this tag include resistance/impedance calculations, filter transfer functions, calculating signal levels at different parts of a circuit, or anything else that may have to do with math or equations.

Questions Q: Why is the speed of light rounded to 286 Mm in calculations involving frequencies below 30MHz? Tags: math (Prev Q), physics (Prev Q) (Next Q) I understand that in order to make the maths simpler, frequency (f ) is expressed in megahertz (MHz) and the velocity of propagation in free space (c) for frequencies above 30 MHz is expressed as and rounded to 300 megameters/second (Mm/s). The actual speed of light is 299,792,458 meters/second, so expressing and rounding this to 300 Mm makes sense. I’m confused why it is rounded to 286 Mm when f < 30 MHz . Please explain. An excellent answer will show the maths. Tags: math (Prev Q), physics (Prev Q) (Next Q) User: dan Answer

by adam-davis

Electrical wave propagation in wire is about 95% to 97% the speed of light. Since wavelength is most commonly used for building antennas, which involve conducting the wave from air into the wire and vice versa, the calculation is adjusted assuming the slower propagation in an unshielded conductor. However, this 3% to 5% discrepancy is small enough at frequencies above 30 MHz that it is usually ignored for simplicity, and 300 is used instead. For frequencies below 30 MHz it becomes more significant and the adjusted value, approximately 95% of 300 Mm, is used instead - about 286 Mm. (300 Mm)(0.95¯3) 286 Mm λm = = f MHz f MHz Tags: math (Prev Q), physics (Prev Q) (Next Q)

Packet Skip to questions, Wiki by user wprecht–ab3ry

What is Packet? While the term can apply to a specific digital mode, it is often used a general label for digital data modes in ham radio. Packet The term “packet” refers to “packet switching”, the basic structure of the network protocol used to transfer information. This is the same basic protocol that runs the Internet. In fact, the common packet protocol is AX.25 a derivation of the Internet’s X.25 protocol. As one of the first “modern” digital modes, packet radio transmits data in groups or “packets” of 10s or 100s of bytes. This allows improved throughput and error control. Transmission speeds typically range from 300 bps on the HF bands to 1200 and 9600 bps on VHF or UHF. Other Digital Modes PSK31 is probably the most popular keyboard to keyboard digital mode in use today. PSK31 is normally generated and decoded using PC soundcards with one of many available software packages. PSK31 occupies very small bandwidths (approximately 100 Hz) and offers effective communication at low power. PSK31 uses Phase Shift Keying for data encoding RTTY (radio teletype) is the original keyboard to keyboard mode, based on the 5-bit Baudot code and it began with mechanical teletypes. It is still a popular communications mode, but now uses PC soundcards for coding and decoding, using 170 Hz frequency shift keying at a 45.45 baud rate — 60 words per minute. For More Information There are many many others. See: HF Digital Modes on Ham Universe for a tabular list of the more popular software packages and the modes they support with links.

Questions Q: Can a Yaesu FT-7900R be physically connected to both KPC-9612+ ports? Tags: packet (Prev Q) The Yaesu FT-7900R has a single data port (mini DIN 6-pin) for 1200 and 9600 bps TNCs. Page 10 of the manual states: In accordance with industry standards, the signal levels, impedances, and bandwidths are significantly different on 9600 bps as opposed to 1200 bps. If your TNC does not provide multiple lines to accommodate such optimization, you may still be able to utilize your TNC, if it is designed for multiple-radio use, by connecting the TNC “Radio 1” port to the 1200 bps lines on the FT-7900R, and the “Radio 2” port to the 9600 bps lines. Is it possible to follow these directions with a KPC-9612+? Tags: packet (Prev Q) User: jacob Answer

by oh7lzb

RX audio: The FT-7900R has separate audio outputs for RX audio on the DIN connector for 1200 and 9600, so those can be simply wired to the two separate KPC-9612+ ports. PTT: The PTT line has a little voltage provided by the radio, and the TNC’s PTT pin grounds that pin to transmit. You can directly wire both TNC port PTTs to the radio, and it’ll transmit when either of the TNC ports ground the pin. TX audio: The correct method would be to provide some mixing circuit to mix the audio signal outputs of the TNC. Some audio level loss is OK, since you can compensate by adjusting the output level of the TNC up, so a passive circuit is good. The most important thing is that the mixing may not affect the frequency response, since it’s quite important for good 9600 bit/s operation. Simply wiring both the 9600 and 1200 bit/s audio outputs of the TNC together might work, or it might not, depending on the type of the outputs on the TNC. A simple resistor mixer might work better. It’s probably obvious, but you’ll have to make sure the two TNC ports don’t transmit at the same time - the transmit audio, mixed 1200/9600 data, would not make any sense. This is a community wiki, so if someone has better details on the TX audio connection, please edit it in. Tags: packet (Prev Q)

Physics Questions Q: What’s this “crossover” toroid winding called and what is its purpose? Tags: physics (Prev Q) I am winding an EFHW matchbox and many of the designs I’ve found (including the diagram provided with the kit I bought) include a sort of “twist” when winding them:

(Image taken from this post

and similar can be seen here

and here

and here


My understanding is that the section where the two green turns go with the initial red turns is called a “bifilar” winding and some recommend twisting the two wires together for that part — its own topic that I can research a bit more on my own. But what is the trick where the red winding crosses across the middle and then continues winding? Does it have a name? Does it count as a turn — or a “negative turn”? (In the diagram I have linked there are drawn 8+7 turns labeled as 2x7…but I suspect this is just a mistake.) Why would the toroids be wound this way in two groups instead of just a simple total number of windings spread evenly around? When is this technique useful? Tags: physics (Prev Q) User: natevw–af7tb Answer

by tomnexus

This is a magnetic flux transformer, not a transmission line transformer. It works by flux coupling just like a mains power transformer. So the bifilar part isn’t too special, nothing like a transmission line transformer. In a regular flux transformer, the position of the winding doesn’t really matter, only the number of turns. At RF though there is the concern about capacitance. First concern is the inter-turn capacitance, which might make the coil resonant and stop working as a transformer. The best you can do is keep the number of turns small, and spread them out evenly. Of course fewer turns means more flux, so there’s a trade-off. The second concern is about the capacitance from one end of the winding to the other. A 64:1 transformer will have a very high impedance at the high voltage end, and any capacitance to the ground end of the winding will tend to load the high impedance end. This transformer might transform to an impractical 3200 ohms, but quite likely the capacitance from live to ground will be less than that. So if you follow the wire, the reverse winding only reverses direction on the core, it keeps going the same way through and out, so it keeps developing more voltage at each turn. The reverse winding is a neat trick to keep the windings spread out, keep them going in the same direction, and keep the high voltage, high impedance end of the transformer far away from the ground. I don’t know it’s name, but I’m sure it will have one. Recommended reading: Jerry Sevik - Transmission Line Transformers Tags: physics (Prev Q)

Location Skip to questions, Wiki by user wprecht–ab3ry

Location Location is one of those important pieces of information that is commonly exchanged between radio amateurs during a QSO. However, there are many systems in place to describe your (or your contact’s) location depending on the situation. This article attempts to be a primer on the most common ones. Lat/Lon—The old standby, the earth is divided into 360° (+- 180°) starting at the Royal Observatory in Greenich England as the Prime Meridian (or 0°). West from here the Longitude is positive, East from here, negative. for the North/South dimension, the Earth is divided into 180° (+-90°) starting at the equator. North of the equator, the value is positive, south of the equator, it’s negative. Both values can be further divided into minutes, seconds and fractions of seconds for higher resolution. GPS Coordinates— Uses a high resolution model of the Earth and precise time measurements to give highly accurate Latitude/Longitude figures as will as altitude. ARRL Section—The ARRL has divided the US and Canada (I imagine in cooperation with RAC) into sections along state/province lines. Populous states/provinces are split into more sections as needed. There are (currently) 86 sections. You can find a nice map here CQ Zones—CQ Amateur Radio Magazine has divided the Earth into 40 zones for the purposes of their contests. You can find a complete description of them here . ITU Zones—The ITU (International Telecommunication Union) is the United Nations specialized agency for information and communication technologies. They have divided the Earth broadly into 3 Regions and further divided down to 90 Zones. You can find good maps here . Grid Square—(Maidenhead Locator System) was conceived as a simple way to describe your general location anywhere on the Earth in a way that’s suitable for easy communication over the air. The Maidenhead Locator System (named after the town near London where it was conceived by a meeting of European VHF managers in 1980), a grid square measures 1° latitude by 2° longitude and measures approximately 70 × 100 miles in the continental US. A grid square is indicated by two letters (the field) and two numbers (the square), as in FN31, the grid square within which W1AW, ARRL’s Maxim Memorial Station, resides. Occasionally you will need to use a subsquare for more precise location. Each subsquare

is designated by the addition of two letters after the grid square, as FN44ig. These more precise locators are used as part of the exchange in the 10-GHz contest. They measure 2.5 minutes latitude by 5 minutes longitude, roughly corresponding to 3 × 4 miles in the continental US. A nice article in the January 1989 QST describes the system and conversion between lat/lon and grid squares: Conversion Between Geodetic and Grid Locator Systems . This website: Grid Square Locator Map will determine your grid square location based on either your address or call sign or is you give it a grid square (either 4 digit or 6 digit), it will show you on a map the area that square encompasses.

Questions Q: How can one convert from Lat/Long to Grid Square? Tags: location (Next Q) I see that many contests, awards, and other items, use Grid Squares as a means to identify where one is. How can one figure out what one’s grid square is, given lat/long? Tags: location (Next Q) User: pearsonartphoto Answer

by pearsonartphoto

First of all, if you don’t want to do any math, then check out a grid square map, such as this one . There is an excellent process at this page , and additional resources from ARRL . Essentially, Grid Squares contain 3 pairs, the first and last letters, and the middle numbers. Longitude is always the first, followed by latitude, for each pair. For simplicity, let’s assume that West and South are negative lat/long, as is a common convention. For example purposes, I’m going to use 32.123 W, 14.321 N. The key thing is to do the following.: Longitude 1. Add 180 to the longitude, and take the integer value /20, and add one. Then figure out which letter of the alphabet that corresponds to, usually written in upper case. The example will be 147.877/20=7. Adding one will give the 8th letter of the alphabet, or H. Note 7.877 is remaining. 2. Take the remainder of what is left, and divide by 2, rounding down. This is the number, no conversion required. The example will give a value of 3. Note 1.877 is remaining. 3. Take the remainder that is left, and multiply by 12, and add one. Round down to the nearest integer.. This is the letter of the alphabet, usually written in lower case. The example gives a value of 22+1=23. This will be the letter w. Latitude 1. Add 90 to the longitude, and take the integer value /10, and add one. Then figure out which letter of the alphabet that corresponds to, usually written in upper case. The example will be 104.321/10=10. Adding one will give the 11th letter of the alphabet, or K. Note 4.321 is remaining. 2. Take the remainder of what is left, and round down. This is the number, no conversion required. The example will give a value of 4. Note 0.321 is remaining. 3. Take the remainder that is left, and multiply by 24, and add one. Round down to the nearest integer.. This is the letter of the alphabet, usually written in lower case. The example gives a value of 7+1=8. This will be the letter h.

Putting them together by pairs, and alternating first longitude then latitude, gives the grid square for 32.123 W, 14.321 N to be HK34wh. Answer

by ossi-väänänen

My first post in SO. Here’s a C version… made this for an Arduino project. Skip code block void calcLocator(char *dst, double lat, double lon) { int o1, o2, o3; int a1, a2, a3; double remainder; // longitude remainder = lon + 180.0; o1 = (int)(remainder / 20.0); remainder = remainder - (double)o1 * 20.0; o2 = (int)(remainder / 2.0); remainder = remainder - 2.0 * (double)o2; o3 = (int)(12.0 * remainder); // latitude remainder = lat + 90.0; a1 = (int)(remainder / 10.0); remainder = remainder - (double)a1 * 10.0; a2 = (int)(remainder); remainder = remainder - (double)a2; a3 = (int)(24.0 * remainder); dst[0] = (char)o1 + 'A'; dst[1] = (char)a1 + 'A'; dst[2] = (char)o2 + '0'; dst[3] = (char)a2 + '0'; dst[4] = (char)o3 + 'A'; dst[5] = (char)a3 + 'A'; dst[6] = (char)0; }


by chris-ac2cz

This helped me. For anyone that needs it, here is a port to Java: Skip code block public class Location { String latlon; String maidenhead; public Location(String p1, String p2) { float lat = -100.0f; float lon = 0.0f; try { lat = Float.parseFloat(p1); lon = Float.parseFloat(p2); maidenhead = latLonToGridSquare(lat, lon); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } public Location(float lat, float lon) { try { maidenhead = latLonToGridSquare(lat, lon); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } private void gridSquareToLatLon(String grid) {

} public String latLonToGridSquare(float lat, float lon) throws Exception{ float adjLat,adjLon; char GLat,GLon; String nLat,nLon; char gLat,gLon; float rLat,rLon; String U = "ABCDEFGHIJKLMNOPQRSTUVWX"; String L = U.toLowerCase(); // support Chris Veness 2002-2012 LatLon library and // other objects with lat/lon properties // properties could be getter functions, numbers, or strings

if (Float.isNaN(lat)) throw new Exception("lat is NaN"); if (Float.isNaN(lon)) throw new Exception("lon is NaN"); if (Math.abs(lat) == 90.0) throw new Exception("grid squares invalid at N/S poles"); if (Math.abs(lat) > 90) throw new Exception("invalid latitude: "+lat); if (Math.abs(lon) > 180) throw new Exception("invalid longitude: "+lon);

adjLat = lat + 90; adjLon = lon + 180; GLat = U.charAt((int) (adjLat/10)); GLon = U.charAt((int) (adjLon/20)); nLat = ""+(int)(adjLat % 10); nLon = ""+(int)((adjLon/2) % 10); rLat = (adjLat - (int)(adjLat)) * 60; rLon = (adjLon - 2*(int)(adjLon/2)) *60; gLat = L.charAt((int)(rLat/2.5)); gLon = L.charAt((int)(rLon/5)); String locator = ""+GLon+GLat+nLon+nLat+gLon+gLat; return locator; } }

And here is the JUnit test case: Skip code block import static org.junit.Assert.*; import org.junit.After; import org.junit.AfterClass; import org.junit.Before; import org.junit.BeforeClass; import org.junit.Test; public class LocationTest { @Test public void testLatLonToGridSquare() { Location loc = new Location(48.14666f,11.60833f); System.out.println(loc.maidenhead); assertEquals(loc.maidenhead, "JN58td"); loc = new Location("-34.91","-56.21166"); System.out.println(loc.maidenhead); assertEquals(loc.maidenhead, "GF15vc"); loc = new Location(38.92f,-77.065f); System.out.println(loc.maidenhead); assertEquals(loc.maidenhead, "FM18lw"); loc = new Location(-41.28333f,174.745f); System.out.println(loc.maidenhead); assertEquals(loc.maidenhead, "RE78ir"); loc = new Location(41.714775f,-72.727260f); System.out.println(loc.maidenhead); assertEquals(loc.maidenhead, "FN31pr"); loc = new Location(37.413708f,-122.1073236f); System.out.println(loc.maidenhead);

assertEquals(loc.maidenhead, "CM87wj"); loc = new Location(35.0542f,-85.1142f ); System.out.println(loc.maidenhead); assertEquals(loc.maidenhead, "EM75kb"); } }

Tags: location (Next Q)

Q: Where can I find the official definition of ITU Zones? Tags: location (Prev Q) (Next Q) I’ve been looking around for a spot that has the official definition of what the various ITU Zones are, but can’t find one. What is the official definition? I’m hoping for more than just a map, unless said map is VERY detailed and can be downloaded as a KML or similar map. Something like the CQ Zone definition would be adequate. Tags: location (Prev Q) (Next Q) User: pearsonartphoto Answer

by pearsonartphoto

Per this document : Larry E. Price W4RA, the IARU president in 2002, requesting the definitive ITU zone definitions - wrote: You have to keep in mind that the ITU has one administrative purpose for having zones that has nothing at all to do with amateur radio. However, various amateur radio organizations decided to have both awards and operating events on the air based on the idea of zones. But, since this is not why the zones exist as far as ITU is concerned, the sponsors of these amateur events are free to interpret the zone boundaries any way they wish. So, there might not be a single “official amateur radio zone list.” For the US & Canada, the interpretation by ARRL is found in The ARRL Operating Manual, desk top reference, page 12 which defines the boundaries between US States and Canadian provinces. If you have more questions about any particular contest or award, they should be directed to the sponsor. So the US official ITU zones are defined by ARRL. Amber has a list of some specified points that define certain zones, plus a rough map. The most official worldwide map is this one, although it is not necessarily the source for data.

HamAtlas has done a very good job of taking the ITU map, and other “Official” definitions, and creating a usable set. This is probably the best definition that exists. Answer

by amber

I found this reference table on the ITU site: That appears to lay out lat/long coordinates for the points outlining the zones. It’s linked to from this page titled “Reference Data”: Tags: location (Prev Q) (Next Q)

Q: What are CQ/ITU zones used for? Tags: location (Prev Q) There are already questions about the definition of CQ zones and ITU zones, but there is no information about what these zones are used for (and Google brings up various maps but no explanation). (Is this something a non-US novice-class amateur needs to know about?) Tags: location (Prev Q)

User: georg-do1gl Answer

by dan-kd2ee

Many contests use them as a convenient measure of how many different “regions” you’ve managed to contact. Since using countries as a contest multiplier isn’t necessarily very accurate (within a certain radius, US can only easily reach Canada or Mexico or ocean, within the same radius, a station in central Europe could easily have their first 20 contacts come from 20 different countries) these equal-sized regions allow for a somewhat more equitable contest scoring system. They also go into awards - there is a Worked All Zones award for the ITU zones, so while getting DXCC (century club - contacts with 100 different countries) may be much easier from Germany than it is from Kansas, both stations will have similar difficulty getting the Worked All Zones award, because the zones are more uniform worldwide than countries are. Answer

by pearsonartphoto

Both are a means of identifying where you are in the world. CQ Zones is managed by CQ Magazine, and the ITU Zones are managed by the ITU. You can see more information about how they are defined in the two questions you linked. Some contests use them as an identifier of where you are, the most notable being the ITU number used in the IARU competition in July, and the CQ Zones are used by various competitions, usually those sponsored by CQ Magazine. Both of these are an entry in to LOTW, which is where I became familiar with them. Most logging programs will ask for your CQ/ITU zone number. I’m sure there’s other places they crop up as well. Tags: location (Prev Q)

ARRL Questions Q: The ARRL handbook updates yearly. Is it useful to buy it every year? Tags: arrl (Prev Q) There seem to be updates to the ARRL handbook every year, but I don’t know if the updates are significant or not. Is the yearly update minor, and buying a new one every 10 years would be enough to avoid missing something important, or is the year-to-year content so different that I should consider buying each year’s volume? Tags: arrl (Prev Q) User: adam-davis Answer

by wprecht–ab3ry

I don’t think there is a right answer here, but I will share mine and the one I suggest to new hams. The ARRL Handbook is an awesome reference, especially for the price. You simply get a ton of information from basic electronics on through all the major areas of amateur radio. With the numbering system they use, there isn’t even a good way to determine the number of pages in any given edition. I think it’s safe to say that it’s current page count is north of 1200 pages and has grown steadily over the years. In fact it was the Handbook that was one of the big draws of amateur radio when I was first introduced to it as a teenager. It was simply the best collection of cool electronic information I had ever seen in one place. It’s too large a product for it to change substantively from year to year; the ARRL just doesn’t have the staff for that. But I think it’s aim, as a handbook/reference is more like an encyclopedia than a be-all reference. And the basics don’t change that much from year to year. What does change are the projects that accompany the articles. These tend to be reprints from QST or other ARRL publications, but none-the-less serve to make concrete examples of the theory presented there. Technology changes and ham radio follows along (or leads!), so I think one every 5 years is probably fine. I have the last 15 years on my shelf, except for the last two years. That’s because I don’t buy them new. As much as I like them, $50 a pop is just too big a chunk of my radio budget this year. But, I probably only spent around US$100 on the 13 volumes I have by buying them used on eBay and at hamfests. For instance, the last copy of the 2010 Handbook that sold on eBay went for US$5.00 and the one that’s up right now is at US$0.99 with no bidders.

Shop wisely and enjoy one of the best references out there. Tags: arrl (Prev Q)

Direct Conversion Questions Q: What are the I and Q in quadrature sampling? Tags: direct-conversion (Prev Q) For some reason I’ve long believed that given I and Q, one corresponds to amplitude, and one to phase, so I thought that I could hold one steady and create AM, or hold the other steady and create FM. Now that I’m delving more into it, though, it appears I’m completely wrong. Or not. I’m not really sure, and the articles I’m reading aren’t helping the situation. Can AM and FM be demodulated from quadrature signals relatively easily? I feel that if I understand this, I might be able to wrap my head around it. Tags: direct-conversion (Prev Q) User: adam-davis Answer

by phil-frost

Your understanding is almost correct. I/Q data represents phase and amplitude, but in Cartesian coordinates . Conversion between the two is elementary trigonometry: −−−−−− r = √ I 2 + Q2 θ = atan2(Q, I) To demodulate AM, you just need r , and to demodulate FM, you just need θ . Usually, an I/Q pair is represented as a complex number , with I being the real part, and Q being the imaginary part. This makes possible some interesting mathematical manipulations like multiplying a signal by a complex exponential to make a mixer. However, unlike a usual (“non-complex”) mixer , this mixer does not make two new signals (sum and difference), but rather just one. This ability to shift a spectrum of frequencies without creating an additional sideband (which must then be filtered out, typically) is a big win in DSP. Answer

by kevin-reid-ag6yo

Quadrature samples are essentially complex numbers. Complex numbers can be represented as two real numbers in two equivalent ways: 1. Cartesian form: real (here called I or in-phase) and imaginary (here called Q or quadrature). 2. Polar form: magnitude (or absolute value) and phase (or angle, or argument).

When you have I and Q signals or samples, those are in Cartesian form. However, when you want to demodulate, or even describe mathematically, a complex signal, the magnitude/phase form is more relevant; this is because the received phase is arbitrary (unless the transmitter and receiver have perfectly synchronized clocks and mixers and the path length never changes), which means that the signal has an arbitrary phase shift and therefore has no specific relationship with your I and Q “axes”. To help understand this, visualize an unmodulated complex (analytic) signal as a helix in 3D space: the axes are I, Q, and time. Unlike a real-valued signal, there are no zero crossings; the sample values follow a circle about the origin over time, and never meet it except when the amplitude is 0. Furthermore, if the signal is baseband (after a receiver’s mixer or before a transmitter’s), then the rotation rate is 0 by definition: your samples have a constant value, except for the effects of the modulation. And this is the condition under which modulation and demodulation are typically done! You ask for analog demodulation examples: Demodulating AM from complex samples consists of taking the magnitude of the samples (and then subtracting the carrier amplitude from that, or equivalently using a high-pass filter), because that is exactly the amplitude of the original signal. Demodulating FM from complex samples consists of taking the difference between the phase of successive samples, because that difference is the instantaneous frequency; if the signal is at baseband, then the instantaneous frequency is exactly the modulating signal! Tags: direct-conversion (Prev Q)

Oscillator Questions Q: Why prefer LC oscillators rather than RC oscillators in RF design? Tags: oscillator (Prev Q) I don’t recall ever seeing an RC oscillator driven RF transmitter or receiver. What prevents people from choosing RC oscillators in RF design? Tags: oscillator (Prev Q) User: adam-davis Answer

by phil-frost

I’m going to discuss filters and not oscillators, because the reasons are pretty much the same. An oscillator is just a filter with enough gain to put it on the edge of stability. It certainly is possible to use RC filters in RF design, and sometimes you do see them in non-critical filters, especially those that don’t require a steep filter or high power handling, such as AC coupling between stages. Reasons you might not want to use inductors: They are expensive to manufacture Real inductors have significant non-ideal properties saturation current series resistance inter-winding capacitance (for transformers, a special case of inductor) leakage inductance Resistors and capacitors also have non-ideal properties (lead inductance) and aren’t free, but the magnitude of these problems is less. Reasons you might want to include inductors in your circuits: A LC circuit has two poles , where an RC filter has only one. You can get two poles with two RC circuits, but often that’s just more components. An inductor’s impedance increases with frequency, while a capacitor’s inductance decreases with frequency. For many filter topologies you need both kinds of impedance (for example, a Pi network ). You can simulate an inductor from a capacitor and an inductor using a circuit called a gyrator , but this has additional disadvantages: The simulated inductance must have some resistance also, limiting Q factor It increases complexity, and requires an op-amp capable of RF operation, which can be hard or expensive at higher frequencies

Related to the previous point, if you have a capacitive impedance (such as all RC filters have), and you want to transform that to a purely resistive impedance (usually, 50Ω), then you need an inductor. Try playing with a Smith chart to see why. Resistors convert electrical energy to heat, where (ideal) inductors do not. Obviously you wouldn’t want anything turning your transmit energy into heat instead of electromagnetic radiation. Answer

by hotpaw2

The transient response of an RC circuit driven to oscillation by negative feedback generates a much higher proportion of harmonics than a similar LC circuits response. These harmonics have to be either filtered out with additional circuitry, or the oscillation needs a significant amount of post-processing (such as using it to clock an SDR or a digital synthesizer), in order to produce a clean enough waveform to meet legal requirements for RF transmission. PLLs in receivers may or may not need as clean a waveform, depending on the receiver design. Tags: oscillator (Prev Q)

Callsign Questions Q: How can I tell if a call sign is valid? Tags: callsign (Prev Q) Many different countries have different callsign formats. The US call signs typically fit into a very well defined category, but there are exceptions even there. I’m looking for a way to tell if a call sign is a real call sign, that works with international call signs. I’m looking for the full call sign, including after a ‘/’. I don’t care if the call sign is actually assigned to a user, just if it is possible to assign the call to a user. I’m looking for rules as to what would be considered valid. A very general sense is okay too. I don’t care if I filter something that could be a call sign, but isn’t actually assigned, like 1S prefix calls, but I do want to make sure I get special edge cases, like W100AW. From what I can tell, the format that is valid appears to include a prefix, which can include up to 1 number and always includes 1 or 2 letters, followed by a number identifier, followed by 1-3 letters. An additional part of the call sign can be included before or after the call that can include a lot of things, including a /AE,/AG,/KH6 (Or other prefix), and possibly other things as well, which I’m not really certain of. I’m looking for something like this, but preferably more detailed. Basically, I’m trying to tell if a callsign is likely to be real, so I can check to see if I have an invalid call sign in my logging program. Tags: callsign (Prev Q) User: pearsonartphoto Answer

by adam-davis

Callsigns, per ITU regulations, consist of a prefix and a suffix. The prefix must be obtained from this table: Table of International Call Sign Series (Appendix 42 to the RR) And is assigned on a per-country basis. The suffix is then determined by that country’s internal radio regulations, and there is no standard that will make this easy for you. You’ll need to research each country’s regulation and standard and include hundreds of different rules if you need to determine validity to that degree. However, you can eliminate a lot of bad callsigns simply by verifying that the prefix is valid, using the above list. The general guidelines on the formation of a whole callsign, including what the suffix may contain, are fairly well explained in this wikipedia article:

ITU prefix (amateur stations) There are rare exceptions, but generally you start with the country prefix, add a numeral, then add a suffix of between 1 and 4 alphanumeric characters. The last character has to be a letter, not a number, but otherwise there’s no regulation internationally. Answer

by pearsonartphoto

Starting with Adam’s answer, I did a bit of research into the matter. Using a list of LOTW call signs , I tried the following regular expression \d?[a-zA-Z]{1,2}\d{1,4}[a-zA-Z] {1,4}, which simply says a number can optionally start, followed by 1 or 2 letters, followed by 1-4 numbers, and 1-4 letters. I’m filtering out any extra parts (Stuff before and after a /. Given this, I still failed on the following call signs: Skip code block 4D71/N0NM 4X130RISHON 9N38 AX3GAMES BV100 DA2MORSE DB50FIRAC DL50FRANCE FBC5AGB FBC5CWU FBC5LMJ FBC5NOD FBC5YJ FBC6HQP GB50RSARS HA80MRASZ HB9STEVE HG5FIRAC HG80MRASZ II050SCOUT IP1METEO J42004A J42004Q LM1814 LM2T70Y LM9L40Y LM9L40Y/P OEM2BZL OEM3SGU OEM3SGU/3 OEM6CLD OEM8CIQ OM2011GOOOLY ON1000NOTGER ON70REDSTAR PA09SHAPE PA65VERON PA90CORUS PG50RNARS PG540BUFFALO S55CERKNO TM380 TX9 TYA11 U5ARTEK/A V6T1 VI2AJ2010 VI2FG30 VI4WIP50 VU3DJQF1 VX31763 WD4 XUF2B YI9B4E


So I guess there isn’t a standard definition, but you should be able to recognize most of them with a similar pattern, and just be aware that there are others out there as well. Tags: callsign (Prev Q)

Amplifier Questions Q: What is a linear RF amplifier? Tags: amplifier (Prev Q) Most of the RF amplifiers advertised, and most of the questions about amplifiers, are “linear” amplifiers. What is a linear amplifier, and what other common amplifier type(s) exist that requires people to say “linear” every time they talk about RF amplifiers? Tags: amplifier (Prev Q) User: adam-davis Answer

by phil-frost

Google defines “linear” as “arranged in or extending along a straight or nearly straight line.” Wikipedia tells me that “linearity refers to a function or relationship which can be graphically represented as a straight line”. Such systems can be described by an equation of the form y = mx + b . In the case of RF amplifiers, the relationship is the input voltage vs. the output voltage. The output is identical to the input, only “louder”. Mathematically, Vout = A ⋅ Vin + 0 , where A is the voltage gain of the amplifier.1 Linearity is a generally desirable property but it comes at the cost of reduced efficiency. At any instant, the amplifier’s output is probably something somewhere between its power supply rails, and consequently, the output transistors will have some voltage E across them and some current I through them. The rate of electrical energy consumption is the product of these two: P = IE . That consumed energy can’t vanish: it’s converted into heat. This requires big heatsinks, and it drains your batteries faster or runs up your electric bill.2 Here’s a solution to the heat problem: we amplify the input signal so much that the output is always greater than the supply rails. Now we are effectively connecting the load directly to one supply rail or the other. Now the output transistors either have 0V across it,3 or are passing no current. Thus, the power (P = IE ) in the transistors is low because always either current or voltage is nearly 0. The energy is going to the antenna, not to heating the transistors. The problem is now that the output is horribly distorted. If the input was a nice clean sine wave, the output will be a square wave, full of odd harmonics. We can remove4 the harmonics with a filter, and because the filter is made of reactive components like inductors and capacitors which alternately store and release electrical energy, rather than

converting it to heat, they don’t get so hot, and the amplifier is more efficient. This mostly solves the distortion problem, but something is lost: the amplitude of the input signal. Fortunately, the frequency is preserved. So now we know when non-linear amplifiers are acceptable: when the amplitude of the signal is insignificant, such as FM, or frequency modulated digital modulations like FSK , some PSK flavors , or GMSK . Modes where amplitude is significant like AM, SSB, or digital modulations like QAM require a linear amplifier. 1: RF amps tend not be to be marketed by their voltage gain, but by their maximum power output. Assuming a 50 ohm load, power is related to voltage by P = E 2 /50Ω . Take the output power and the input power, calculate the associated voltages, and the ratio of the two is the voltage gain of the amp. 2: To dive more deeply into the reasons linear electronic circuits make waste heat, check out My linear voltage regulator is overheating very fast on electronics.SE. Though that’s about voltage regulators, the problem is common to a broad class of linear electronic circuits. You can also read about power amplifier classes . Class AB is a common linear RF amplifier design. Class C is common for non-linear amps. 3: Real transistors will always have some small voltage across them, even when fully on, which means they will get a little warm. This is far better than the a lot warm they get in a linear amplifier, however. 4: really, just attenuate. Significantly and sufficiently. All amplifiers output harmonic distortion of some degree, and regulatory agencies regulate the maximum allowable harmonic distortion.

Tags: amplifier (Prev Q)

Sunspots Questions Q: Why is the solar-flux index measured at 10.7 cm? Tags: sunspots (Prev Q) Why is the solar-flux index measured at 10.7 cm? What makes that such a special frequency? Tags: sunspots (Prev Q) User: dan Answer

by amber

So as it turns out, the reason behind this is fairly simple: the first receiver that was used to take recordings which wound up being linked with solar flux operated at 2800MHz (and thus a 10.7cm wavelength). In order to allow historical comparison of readings, that wavelength has been preserved ever since. Here’s an article with the full origin story Answer


by bogdanovist

The component of the solar flux that actually impacts the ionospheric strength is the Extreme Ultra Violet (EUV) part of the spectrum. This is what causes the ionosation that produces the ionosphere. However, because the EUV is being absorbed by the upper atmosphere, it (fortunately!) doesn’t make it to ground (at least the flux is much much lower at ground level). This means ground based receivers can’t get a good handle on the actual solar EUV flux. In modern times we have access to satellites that measure the EUV flux outside the atmosphere. Historically, there are two main proxy measurements of the EUV flux. The oldest is sunspots. Since the EUV is emitted from sunspot regions, the more sunspots the higher the EUV flux and hence the stronger the ionosphere. The 10.7cm radio flux was serendipitously found to also correlate with the sunspot number in the years after WWII. The physics behind this is complex, and not fully understood. Empirically though, there is a non-linear relationship between sunspot number and 10.7cm flux that has held for several decades. The 10.7cm flux is a simpler measure than subjectively counting sunspots and can be performed during cloudy weather. Interestingly, during the last 5-10 years, the relationship between sunspot number and 10.7cm solar flux has been changing, most probably due to an overall weakening of the solar coronal magnetic field as the Sun moves into a quieter phase after the space age ‘grand maximum’ that has been experienced over the last 50 years or so.

Going forward, direct EUV measurements from satellites are becoming a more predominant method of measuring solar flux as relevant to the ionosphere although 10.7cm radio noise will still remain an important ground based back-up for many years. Tags: sunspots (Prev Q)

Logging Questions Q: Does LOTW have an interface document? Tags: logging (Prev Q) I want to be able to sign my own LOTW entries, without using the provided library (My application is pure Java). Is there a document that explains in enough detail how to do this, assuming of course that I’m provided with a certificate (.tq8 I believe)? Tags: logging (Prev Q) User: pearsonartphoto Answer

by pearsonartphoto

After looking through things for quite some time, and asking around, I was able to find the following, assuming that I can get a copy of the signed certificate from somewhere. There is some more information at this blog article , and this GitHub site . 1. The log file is done in a format called GAbbI (Global Amateur Interchange) file format is similar to ADIF, but not quite identical. 2. The signature is performed using X.509 certificate handling. 3. The station data is a field in the GAbbI format. 4. The file is then gzipped, and uploaded to ARRL.

. This

Bottom line is, following the specification given through the linked site is the best bet to getting this to work. X.509 is a standard library, and the GAbbI format is close enough to ADIF that it should be relatively easy to parse through. A few things to note that are different from the GAbbI spec: All of the data for signing is upper case. The order of fields for the signed data is: CA_PROVINCE, CQZ, GRIDSQUARE, IOTA, ITUZ, US_COUNTY, US_STATE, BAND, BAND_RX, CALL, FREQ, FREQ_RX, MODE, PROP_MODE, QSO_DATE, QSO_TIME, SAT_NAME. Note that station comes first, then QSO data. There are several undocumented fields, including CA_PROVINCE, US_STATE, SIGNDATA, and SIGN_LOTW_V1.0. SIGNDATA is the data signed for the LOTW signature, SIGN_LOTW_V1.0 is the LOTW signature itself. CA__PROVINCE and US_STATE are the Canadian Province and US state. SIGN_LOTW_V1.0 has a :6 after the number of digits. I suspect this is related to the base 64 output. The max space per row is actually 64, not 72 as specified.

The character count includes line breaks, and if there is any line breaks, it also counts the last line break. For a single line, it doesn’t count the final line break. The signature is signed as SHA1withRSA. Tags: logging (Prev Q)

Dummy Load Questions Q: How do I know if my dummy load is working? Tags: dummy-load (Prev Q) I understand why a dummy load is used, but (aside from it getting hot) how do I know if it’s doing it’s job and doing it’s job well? In my specific case, I’m using a Hack RF One SDR 50 Ohm .

and a Souked SMA Dummy Load

Tags: dummy-load (Prev Q) User: m6jny Answer

by kevin-reid-ag6yo

A dummy load, or terminator, consists of a non-inductive power resistor (or multiple resistors in series and parallel) and a heat sink, both rated for the maximum power to be dissipated. The simplest test on a dummy load you can perform is to measure it with an ohmmeter — it should be 50 Ω (or whatever the specified impedance is). Wiggle the connections while you’re doing this to make sure it does not have an intermittent open circuit — I’ve found this to be a problem with some cheap terminators. The above test tells us that it is 50 Ω at DC, or 0 Hz. It is possible that its impedance will be something else at higher frequencies; if it is, this is a design flaw (or limitation), because this impedance is affected by the geometry of the conductors between the resistor and the input connector. If you wanted to test this property, you would want an antenna analyzer which can sweep over the relevant frequency range and report the impedance or SWR, which you would check for being reasonably close to 50 Ω. If you already have a transmitter, then you can in principle use a SWR meter combined with the transmitter, but most SWR meters that are sold separately are not sensitive enough for this little power to produce any reading at all. Additionally, the entire point of using a dummy load at all in this low-power situation is to avoid impedance-mismatch reflections damaging the transmitter (or triggering protective power fold-back), and if you need to test the dummy load then you in principle don’t know whether there will be reflections or not, so it’s not a safe test. In theory. A dummy load should have the expected impedance, but so does an antenna. The difference between a dummy load and an antenna is that the dummy load mostly does not radiate. To test this characteristic, you would use a receiver to determine the

radiated signal strength — ideally one with a signal strength meter (S-meter or RSSI). (You could use a field strength meter for calibrated results, but if you have that specialized gear…) Note that there will always be some radiation — if not from the dummy load, then from the transmitter. No shielding is perfect. (And the HackRF One has no shielding, anyway.) The final characteristic of a dummy load is power handling capability. To test this, increase transmit power until you smell smoke, then buy a replacement! But you’re not going to manage that with the HackRF One. I wouldn’t even expect any noticeable warmth. Tags: dummy-load (Prev Q)

Echolink Questions Q: How can I participate on Echolink with my Android phone? Tags: echolink (Prev Q) I want to use my Android mobile phone to send and receive over Echolink, like if I was using an amateur radio station. How can I do that? I’m a SWL and only plan to listen until I get my license, and my brother does have a valid amateur radio license. Tags: echolink (Prev Q) User: renish-a-r Answer

by adam-davis

There is at least one app on the Google app store which will connect to echolink, which can be found here: There are other apps that may also connect to Echolink, or are otherwise useful for Echolink users: Tags: echolink (Prev Q)

Tone Squelch Questions Q: Why are PL tones strange numbers? Tags: tone-squelch (Next Q) PL tones have very specific odd numbers with a decimal place like 103.5 or 107.2 or 88.5. The only PL tone that does not have this decimal is the 100.0 hertz tone. Why don’t they just use integers with a standard increment of lets say 10 hertz so it would just be 100, 110, 120 etc. instead of the random numbers? Tags: tone-squelch (Next Q) User: skyler-440 Answer

by jcoppens

Greg Hewgill’s answer is correct, but merits a slight explanation. 1. Constant (percentual) relations mean that the Q-factor of the detector for the tones remains constant. Most detector chips (like the old NE567) and algorithms are designed for a single Q, and the frequency changes don’t change the Q. 2. Distortion is quite normal in electronics — low tones like these are no exception. In fact, they are more sensitive than others as the audio channel was designed for higher (voice) frequencies. A side effect of distortion is what is called intermodulation: new frequencies being generated by the presence of two (or more) other signals. For example, if the subtones were 100, 105 and 110 Hz, then the second harmonic of 105 (210) minus the first (100Hz) could conceivably generate a difference of 210 − 100 = 110 Hz, which would be the next subtone, and could possibly trigger some detector. This cannot happen with the actual tone. 3. You may have noticed that the DTMF basic tones are also organized in a similar way — for the same reasons. In fact, the musical notes on any instrument are like this, because our ears discern differences in a similar way to detectors — constant Q. I am not sure why the separation was chosen to be 1.035, but the exceptions are very probably because the tones which are near multiples of 60 and 50 Hz are shunned because of mains frequency interference, which can filter into the signal via power supply issues/microphone cables, etc. Answer

by greg-hewgill

The ratio between PL tones is roughly constant. From a list of PL tones

, you can

calculate the ratio between each frequency, which turns out to be about 1.035 (with some exceptions, not sure why). Using a constant ratio rather than a constant difference avoids two different tones being exact multiples of each other. If you used a constant difference of 10 Hz, then you would have both 100 Hz and 200 Hz which would tend to interfere with each other, as a detector will be more reliable when the target tones are not integer multiples of each other. With the constant ratio scheme, that won’t happen. Tags: tone-squelch (Next Q)

Q: Would it be possible to transmit all CTCSS tones at once? Tags: tone-squelch (Prev Q) What happens if all CTCSS tones are transmitted at once? Would it trip all radios listening on that frequency? Tags: tone-squelch (Prev Q) User: richard-hum Answer

by kevin-reid-ag6yo

You could get several different results, depending on exactly how the receiver recognizes the expected tone. From a small amount of web research, it sounds like the usual methods are either a filter passing only the expected tone, or a frequency counter which determines the frequency of the tone in the signal which is then compared with the expected tone frequency. If the receiver uses a filter to detect the tone, then its squelch will open, because it doesn’t care about any other part of the frequency content of the signal. If the receiver uses a frequency counter to detect the tone, then if all the tones are close enough to equal strength, the counter will not have a valid output, just as if there was no tone at all (only noise) in the relevant frequency range. However, there is likely to be some non-flat frequency response somewhere along the way, so one particular tone will win and the squelch will open only if that tone is the one the receiver is expecting. You will also run into issues transmitting all the tones at once — your audio signal will have high peaks as the tones beat against each other, and you will have to keep the total amplitude low to avoid over-deviating/distorting — quite likely low enough that the individual tones aren’t strong enough to be recognized as CTCSS tones. I thought I’d see what the actual result is, so I wrote a program with GNU Radio to synthesize the combination of all tones listed on Wikipedia’s page . In order to prevent the output from clipping (analogous to overdeviating in an analog FM signal), I had to set

the amplitude of the individual tones to 0.05 (-26 dB), which is significantly below the 0.15 (-16 dB) level that Phil Frost’s answer said is normal for CTCSS.

Skip code block #!/usr/bin/env python from gnuradio import gr, blocks, analog

sample_rate = 44100 tones = [67.0, 69.3, 71.9, 74.4, 77.0, 79.7, 82.5, 85.4, 88.5, 91.5, 94.8, 97.4, 100.0, 103.5, 107.2, 110.9, duration = 10 gain = 0.05 t = gr.top_block() sum = blocks.add_ff() out = blocks.wavfile_sink("out.wav", 1, sample_rate, 16) t.connect( sum, blocks.head(gr.sizeof_float, int(sample_rate * duration)), out) for i, tone in enumerate(tones): t.connect( analog.sig_source_f(sample_rate, analog.GR_SIN_WAVE, tone, gain), (sum, i))


by phil-frost

No, you can’t. Based on the particular method the receiver uses to decode CTCSS, multiple tones may or may not be recognized. But that’s moot, because you can’t transmit all the tones anyway. CTCSS adds a low frequency tone to the baseband input to the FM modulator. Standards vary, but the amplitude of this tone is around 15% of the deviation. The amplitude needs to be high enough to allow for reliable detection above the noise floor, while low enough to allow the intended transmission (your voice, etc) to also be modulated without overdeviating. Let’s just use round numbers to make the math easy and say the deviation is 10 kHz. That means the CTCSS tone will be responsible for deviation of 1.5kHz, leaving the other 8.5 kHz of deviation available for the intended transmission. If you transmit two tones, you’ve doubled the power of the CTCSS tones. The deviation also increases, leaving less headroom for the intended transmission. Still workable, I suppose. Presuming of course that the decoder will recognize this as valid. But if you transmit all the tones, there just isn’t enough deviation left to transmit all the tones at the specified power. When you add the power of all the tones together, you won’t even be able to transmit them without overdeviating. You could reduce the power of the

tones to avoid overdeviating, but then whatever tone happens to be the right one at the decoder will no longer be strong enough to be detected. So, you can transmit a horribly distorted signal, or a tone too weak to be detected. Tags: tone-squelch (Prev Q)

Voltage Questions Q: Is there a digital multimeter that is more interesting for a ham than a run-of-the-mill model? Tags: voltage My 22-years old Fluke 79 died on me today… Luckily, it was a quiet dead, but nonetheless it left me a bit emotional… So, I am in urgent need of a replacement digital multimeter. This made me wonder whether there would be a model around that is more interesting to own for a radio amateur? Perhaps one with an RF-probe included? Or should I just go with a run-of-themill model? Tags: voltage User: on4aa Answer

by on4aa

Living down-under and apparently also off-the-wall, hyper-enthusiast David L. Jones made following excellent digital multimeter (DMM) reviews: EEVblog #91 – $50 Multimeter Shootout : Extech EX330, Amprobe AM220, Elenco, Vichy VC99 & GS Pro-50, EEVblog #99 – $100 Multimeter Shootout : Extech, Amprobe, BK Precision, Ideal, UEi & Uni-T. David actually opens up all multimeters for a thorough and very revealing inspection. His very surprising findings made me conclude that you really get what you pay for. So it might be more advantageous to open the wallet a little bit wider whilst ignoring the special gimmicks… For example; the VC97 measures up to 30MHz, but its construction is not so great. At the end of the day, I was able to repair my Fluke 79 which, by the way, does measure capacitance. Another review by robot-room also deals with the RSR MS8268 digital multimeter which, unfortunately, was not included in the reviews mentioned above. Answer

by bill–k5wl

I believe the Fluke 79 did not have inductance/capacitance measurement built in. This is an affordable feature on modern multimeters which is quite useful for the ham. For example, it can be used to measure inductance on self-wound toroids which are used in

kit-built radios and for repairs when OEM parts are not available. Likewise, capacitors are often unlabelled or poorly labelled these days, so it can help with that too. Tags: voltage

Ehf Questions Q: Ham radio above 275 GHz Tags: ehf I see on the allocation chart all modes and frequencies are allowed above 275 gigahertz. Has anybody experimented with this? Are there interesting things you can do on these extremely high frequencies? The bandwidth must be amazing here; maybe someone could make something like wifi but faster! How is it even possible to make the electronic circuits operate at these frequencies? Tags: ehf User: skyler-440 Answer

by adam-davis

Occasionally you’ll find researchers and amateur radio enthusiasts who have created transmitters and receivers that operate in the EHF band . This band goes from 30GHz to 300GHz, and covers the frequencies you are interested in. At these frequencies, conventional electronics and oscillators aren’t very useful, and typically oscillators are built by using resonant cavities. This is akin to a pipe organ, but at radio frequencies. One example is the magnetron in the typical microwave oven - while it operates at a much lower frequency, it uses the same principle. At higher frequencies you might use a Klystron , which is a special tube that contains the parts needed to create an EHF oscillator while controlling the amplitude, frequency and phase. The Klystron may be used as the antenna itself as well, directing what you might consider a microwave beam of radio energy, or the energy might be coupled into suitable coaxial cables as in a typical radio setup. The Klystron and Magnetron technically operate on different principles, but they are both examples of ways to generate EHF waves. Note that the next band up, running from 300GHz to 3,000GHz, referred to as terahertz, is the same band that newer airport scanners run at, imaging human bodies below their clothing. Many frequencies in EHF and THF bands will not travel very far through many materials, and so aren’t very useful for general radio use. But there are specialized uses where these frequencies are used, such as airport security scanners and particle accelerators. If you are looking for faster wifi, keep in mind that we haven’t fully exploited the spectrum we’re already using. MIMO is being used to double and triple throughput, for instance. Channel bonding and wider channels are being used it increase throughput.

Going another 10 GHz higher isn’t going to buy us much with our current technology, but will further limit transmission range and penetration. Tags: ehf

Qsl Card Questions Q: What information should be on a QSL card? Tags: qsl-card Like it says in the title. When you design a QSL card (intended for use for both local VHF-and-up contacts as well as international HF contacts), what information needs to be present, and what information might be considered “nice to have” but not strictly needed? Tags: qsl-card User: michael-kjörling Answer

by wprecht–ab3ry

QSL cards vary greatly in design and is one of those areas of creativity. Some hams end up with fancy double sided full color cards, spending a lot of $$. But they could be simple as well; just text with the pertinent information on it. Need to have info: Your call sign (on both sides) Your mailing address (so you can receive a reciprocal card) Details of the contact: Call sign of the remote station (thanks Michael) band or frequency of contact mode of contact (SSB/FM/CW/etc) date of contact (in UTC) time of contact (in UTC) signal report whether or not you want a reciprocal card Nice to have info: Your Maidenhead Grid Square location Your county (in the US) Your Lat / Long A cool picture of your area to make them wish they lived in the same paradise you do :) Tags: qsl-card

Optical Questions Q: Can X-rays be used for communication? Tags: optical I keep increasing my frequencies and want to get up the spectrum more and more. My current project is pointing a powerful focused LED from a peak and I will try to pick it up with a telescope and some sort of photo detector to receive the AM light. I keep wondering about even higher frequencies. I am assuming Ultra violet should not be too much more difficult than Light unless the air absorbs that band. So, going higher, could x-rays be used to communicate, maybe just CW or is it not possible at all and x-rays will not propagate. Tags: optical User: skyler-440 Answer

by adam-davis

If you can control its emissions, and detect it, then you can use it for communications. Xrays are no exception. However there are many reasons they are not widely used, including expensive and limited optics, short distance line of sight outside a vacuum, and not as safe as many other forms of communications. Still X-rays have some uses and there are X-ray communication systems in development. They can be used over vast distances in space with relatively low power, can communicate with spacecraft during re-entry when traditional communications are disrupted due to electron activity in the heat of re-entry, and can penetrate some types of RF shielding, which has some interesting use cases. Tags: optical

Untagged Questions Q: Does amateur radio induce a health risk? Tags: untagged Electromagnetic Exposure wise, does Amateur radio (Particularly 1.8 to 440 megahertz) induce a health risk due to RF radiation? Other than the Maximum Permissible Exposure (MPE) limits, which will cause RF burns etc., are there any studies that show long term usage of radio being bad for you? Tags: untagged User: skyler-440 Answer

by phil-frost

Sure, there are plenty

. Unfortunately, they all seem to be selling

The scientific consensus is quite clear: no known obvious risk of being cooked which MPE limits are set to avoid. Tags: untagged

something risk


, beyond the

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