Lyonodyne DX Crystal Set, DX Crystal Radio

Table of contents :
41-designing_a_dx_crystal_set......Page 1
250635298-The-Secret-to-High-Performance-Crystal-Radios......Page 7
3182474863_284672772e_b......Page 37
Experiments with LC circuits......Page 38
Experiments with LC circuits......Page 42
Experiments with LC circuits......Page 44
Experiments with LC circuits......Page 46
Experiments with LC circuits......Page 49
Experiments with LC circuits......Page 53
Experiments with LC circuits......Page 56
Experiments with LC circuits......Page 58
Experiments with LC circuits......Page 61
Experiments with LC circuits......Page 63
Experiments with LC circuits......Page 66
FET amplifier for measuring LC circuits......Page 68
sguardo sul......Page 75
sguardo sul_0001......Page 76
sguardo sul_0002......Page 77
sguardo sul_0003......Page 78
sguardo sul_0004......Page 79
sguardo sul_0005......Page 80
sguardo sul_0006......Page 81
sguardo sul_0007......Page 82
sguardo sul_0008......Page 83
sguardo sul_0009......Page 84
sguardo sul_0010......Page 85
sguardo sul_0011......Page 86
sguardo sul_0012......Page 87
handbook01......Page 88
handbook02......Page 158
handbook10......Page 296
LYONODYNE Beginner who wants to build - The RadioBoard Forums......Page 442
LYONODYNE Beginner who wants to build - Page 2 - The RadioBoard Forums......Page 451
LYONODYNE Beginner who wants to build - Page 3 - The RadioBoard Forums......Page 460
LYONODYNE Beginner who wants to build - Page 4 - The RadioBoard Forums......Page 466
LYONODYNE Beginner who wants to build - Page 5 - The RadioBoard Forums......Page 471
LYONODYNE Beginner who wants to build - Page 6 - The RadioBoard Forums......Page 476
LYONODYNE Beginner who wants to build - Page 7 - The RadioBoard Forums......Page 484
LYONODYNE Beginner who wants to build - Page 8 - The RadioBoard Forums......Page 489
LYONODYNE Beginner who wants to build - Page 9 - The RadioBoard Forums......Page 493
Lyonodyne Crystal Radio......Page 495
lyonodynewithvariocoupler......Page 500
Measuring the Q of LC circuits......Page 501
Picture001-1......Page 507
Picture001a-1......Page 508
Picture002-1......Page 509
Picture002a-1......Page 510
Picture002a-2 (1)......Page 511
Picture002a-2......Page 512
Picture002a-4......Page 513
Picture003a-1......Page 514
Picture003a-3......Page 515
Picture005-1......Page 516
Picture007a......Page 517
Picture009......Page 518
Picture014a......Page 519
Picture015a......Page 520
Picture016a......Page 521
Picture018a......Page 522
Picture021a......Page 523
Picture023a......Page 524
Picture024a......Page 525
Picture025a......Page 526
Picturea-1......Page 527

Citation preview

DESIGNING A DX CRYSTAL SET by Mike Tuggle 46-469 Kuneki St. Kaneohe, HI 96744-3536 E-Mail: [email protected]

Long distance reception

with crystal radios is once again becoming a serious pursuit among hams and other radio hobbyists. They are discovering that the DX capabilities of these receivers have been greatly underrated. I've been particularly interested in crystal sets since 1959, when I first discovered you could actually DX with them. The Internet has aided crystal set DX activity by making exchange of ideas between likeminded enthusiasts much, much easier. This article only touches the surface from a personal perspective. The reader is encouraged to pursue the online resources, described below, covering all aspects and providing further examples of this fascinating hobby. In this article I'll cover general design considerations for building DX crystal sets, but will leave the actual construction specifications up to you.


Figures 1 and 2 show an example of a DX crystal set. I call it the "Lyonodyne-17." The design evolved from an earlier version described in the November, 1978 OTB. As you can see, this is not your grandfather's crystal set. Antenna (right) and detector (left) tuners are mounted on the middle board. Wave traps are located fore and aft on separate boards, making it possible to adjust the coupling by moving the boards. The antenna coil (L1) is wound on a short ferrite rod. The matching transformer unit for my RCA "Big Cans" sound powered phones is at front, left.

So, what makes a crystal radio a "DX" set? Well, this one is double-tuned (L1-C1 and L2-C2) for selectivity to tune weak DX stations in the RF jungle we now live in. Some DX sets resort to triple tuning for even more selectivity -depends on how many hands you have to do the tuning. The wavetraps (L3-C3 and L4-C4) can be tuned to reject strong unwanted stations in the manner of the notch filter on a communications receiver. Coils L2 through L4 are basket-wound litz wire for low loss and high Q. Variable capacitors C1 through C4 are highest-quality, silver-plated, ceramic-insulated units-as perhaps only the military could specify. All these components are isolated from the mounting board by ceramic standoff insulators. Overkill maybe, but why take chances?

Design Principles

Two fundamental principles underlie DX crystal set design and construction: use of low-loss components and proper impedance matching between stages. Avoid the temptation to construct the set with vintage components. The result may be a handsome set that is only a fair performer. I have such sets, and they sit up on the shelf and look nice. However, for ultimate performance, one should rely on top quality (usually modern) components and materials. This is especially important for tuning capacitors, coil wire and forms, and detector diodes. Layout and construction, particularly in the RF-carrying sections (antenna through detector), should follow good HF practices: short direct leads, careful insulation of components, and avoidance of switches, taps and other trappings in the 'hot', RF-carrying sections. The crystal set, like any other radio, consists of a series of stages--each with a function, each coupled to the next. The stages of a simplified crystal receiver are diagrammed in Figure 3. The resistances shown are used for detailed circuit analysis that will not discussed here.

We have, from left to right: antennaground system, front-end (antenna) tuner, secondary (detector) tuner, diode detector, audio matching and finally, phones. Maximum transfer of available signal power from one stage to the next happens when the impedances of these stages are matched to each other--from antenna to phones--and indeed, from phones to one's ears.


A good outside antenna-ground system is essential for DXing. Loop antennas do not have enough pickup to be effective. An inverted L longwire 20 to 30 feet high and 50 feet long is a good start. The one truth to antenna design is, "higher is better." Any effort expended to raise the antenna, even a few feet, will be amply rewarded. In the most recent crystal set DX contest a third design principle emerged: A huge antenna can overcome shortcomings in the first two principles. The winner suspended 140 feet of litz wire near vertically using helium-filled balloons. Another high-scorer just happened to have a 140-foot tall base-insulated tower and four 1000-foot Beverage antennas to complement his junk box set. Most of us have neither the real estate nor the rigging capability to put up one of these 'mega' antennas. So it behooves us to heed principles 1 and 2. The front-end (antenna tuner) design shown here is one of several that can be used. This particular design tunes a wide variety of antenna-ground systems. Other DX crystal sets use a simple series tuning circuit effectively-especially on long antennas. The diode detector provokes more mystery, controversy and debate than any other component. Some folks favor low-resistance germanium diodes like the 1N34A or rock stands with galenas. Others swear by high-tech Schottky diodes. The emerging truth is, there is no universally perfect diode. The 'best' diode depends specifically

upon the set it is used in. Per the second principle, the diode needs to match the tank circuit feeding it and the transformer and phones that it feeds. With some care, a high-Q tank with litz wire coil and a modern, military-grade variable capacitor can attain a resistance of from several hundred kilohms up to a megohm. Only Schottky diodes and a few modern germanium diodes have resistances this high. The old catswhisker-rock stand detectors have far lower resistances. The most practical approach to selecting the right diode is to apply an A-B listening test to a number of them. Two diodes are mounted in a test stand arranged to quickly switch between them. Using a fairly weak station, one can test a pile of diodes, pair-wise, keeping the winner after each test, until the ultimate one is found. But it's most important to realize that this diode is 'best' for the particular set it was tested in. It may be a quite poor performer in a different set. Surplus, sound-powered (more properly, balanced-armature) phones have become the industry standard for DX crystal sets. Baldwin Type C's were an early example. Now, post-WWII surplus units made by RCA and US Instruments Corp. (USI) are preferred. These phones are low impedance and must be matched to the highimpedance tank (L2-C2) and detector diode by an audio transformer having, typically, 50- to 600-ohm and 50- or 100-kilohm windings (Figure 4). The quality of the transformer is very important, so that its insertion loss is small. UTC input transformers have a good reputation for low loss. The final touch is a comfortable set of headphone cushions for good acoustical coupling to the ears and exclusion of outside noise.

DX Experiences

Under favorable conditions, medium wave or broadcast band DX crystal sets can receive hundreds of stations--some of them thousands of miles distant. In fact, DX crystal set performance is comparable to any other radio (powered or not) short of a full-blown communications receiver with its own outside antenna. The rule of thumb is, if you can hear them on a radio, you can hear them on a crystal set. The best times to listen are at sunrise and sunset, when stations are signing on or off, raising or dropping their powers, and changing their antenna patterns. These circumstances make for a jumble of regional stations ripe for the picking. Deep night is usually the best time for flat-out DX. In 15-year stints at two locations in Maryland, I accumulated logs of over 600 and 400 stations, respectively. The most distant receptions, at 1800 to 2200 miles, were a few powerful stations in the Caribbean area and adjacent South America. I was aided, no doubt, by the largely water path between them and me. The farthest overland station was in Denver at about 1500 miles.

When I moved to Hawaii, I wasn't sure what to expect. The local Honolulu stations were givens. But what about the outer islands? And all-importantly the next stations, mainlanders, the closest some 2400 miles away? As it turns out, Hawaii is an ideal DX location--for distance if not for sheer numbers of stations. With no regional stations, sunrise-sunset activity is non-existent. West coast 500-watt stations, 2500 miles distant, have been heard here. High-power stations in Cuba (4800 mi.) and the Caicos Islands (5500 mi.) have also been heard, thanks to a mostly water path. Stations from the "interior" also make it over. Last year, it was neat to hear KRVN in snowbound Nebraska (3600 mi.) using a homemade cat's whisker mineral detector. This must be what it was like in the old days. With low station powers and crowding, medium-wave broadcast band DXing represents the greatest challenge. On short wave there's no limit to the distance-reception is truly worldwide. I occasionally hear the South African broadcasts nearly 12,000 miles away; Johannesburg and Hawaii are nearly at antipodes. From the mainland, Australia (11,000 miles) was a routine catch. Figures 5 and 6 show my "12,000-mile" crystal set.

Crystal Set DX Activities

Crystal set DX activities include discussion forums sharing ideas and results, an annual DX listening contest now into its sixth year, and the occasional set-building contest where some remarkably high-caliber craftsmanship comes to the fore. All of these activities are served up on the Internet. The following site is a highly recommended grand portal to the wonderful world of crystal set DXing: Owen Pool's Crystal Radio Resources at The comprehensive set of links here covers all aspects of the hobby. This site is headquarters for the annual crystal set DX (XSDX) contests open to everyone. The contest usually takes place in late January. Watch for announcement of specific dates and rules. My own experiences over the years have led me to shed my skepticism of the incredible DX reports made by old-timers back in the early days. Component technology was not what it is today, but circuit technology was, and the sparsely populated bands back then had to be a lot more DX-friendly. You may want to pull an antique crystal set off the shelf and give it a spin. I'd encourage it. Some of these old sets are extremely well built. The construction of the military BC14A/SCR-65 never ceases to amaze me--and others were built just as well. But to start out, I'd recommend conceding to modern technology by using a good, modern diode and sound-powered phones with matching transformer. With just a little luck, prepare to be amazed all over again!

High Performance Crystal Radios Don Asquin, Gord Rabjohn (Presented by Gord at the Ottawa Electronics Club, April 2012)

Childhood History

• Like many kids, I had frustrating childhood experiences with crystal radios! • Simple crystal sets couldn’t separate multiple AM radio stations. • Only local stations were received, and everything was received all at once.

Rediscovering History

• Recently, my friend Don Asquin and I decided to build high performance crystal sets. • Much of this exploration is rediscovering the knowledge of the 1910s and early 1920s. • Even then there were claims of DX performance with crystal sets.

How does a basic crystal set work?

A rectifier A filter At low frequency, the inductor shorts the signal out. At high frequency the capacitor shorts the signal out. In-between, there is a magic point called “resonance”

• Antenna couples to the (usually) electric field in a radio wave. • L-C selects the frequency. • Diode rectifies it. • Earphone makes it audible

AM modulated signal

RF Carrier frequency (say 1310kHz): the filter selects only this frequency.

Rectified audio output, smoothed by the capacitor

The Four Key Elements • Antenna – Antenna – Ground

• Tuner – Loose coupler – High Q coils – RF impedance matching

• Detector • Audio Transducer – Audio Impedance matching

Antenna • A long exterior antenna is crucial. • Why? It’s not just about area… “watts per acre”. It’s also about giving the antenna a better “radiation impedance”. – The energy from an antenna, can be modeled as a voltage source in series with a source resistance (or a current source in parallel with a source conductance), and the antenna capacitance (or inductance). – Radiation resistance is the resistance of this apparent source of energy in an antenna. – The tuned circuit matches this impedance to the load (detector) for optimum energy transfer. – A small antenna will tend to look like a “difficult to match” impedance….

Ground • The ground provides the completion of the current path for the radio signals. • You can always attach a wire to a cold water pipe, but the best ground remains a copper plated rod pounded into the ground. • Home Depot sells these rods for grounding electrical systems. • If installed near a water tap, the ground can be kept moist and conductive.

Tuner -Antenna Tuner



Tuggle (Series / Parallel)

• To extract the most power, you need to match the resistance of the load (detector and earphone) to the impedance of the source (antenna) • The function of the tuner is to match the radiation resistance of the antenna to the impedance of the detector, and to provide selectivity.

Tuner -Loose Coupler

• The loose coupler is simply two coils (each generally resonated with a capacitor) lightly coupled to each other. • One coil is connected to the antenna, the other is connected to the detector. • Even cheap capacitors tend to be quite good, but high Q inductor fabrication is an “art”.

Loose Coupler Response, dB

Loose Coupler Response, Different Coupling Coefs 0 -5 -10 -15 -20 -25 -30 -35 -40 -45 -50


Critical Coupling Over-coupled:Too broad

Under-coupled:poor energy transfer k=0.03 k=0.011 k=0.0039 k=0.0014 k=0.0005


0.98 1 1.02 Frequency, MHz



Simulation of 1000pF, 1.0 ohm antenna, 100uH primary coil and ~330pF cap, coupled to a 100uH secondary coil, 250pF cap, 100k load.

• There is an optimum amount of coupling between the coils. (=1/Q). This is VERY LIGHT coupling. Under 1% of the magnetic field is coupled.

Coil “Q” = Quality


Frequency Bandwidth Station Frequency (kHz) 540 1000 1600

Minimum Q 54 100 160

Assume Q=160 Station Audio Frequency Bandwidth (kHz) (kHz) 540 1.7 1000 3.1 1600 5.0

• For a tuned circuit “Q” is the ratio of the center frequency to the bandwidth. • For a coil, it is the ratio of energy lost to energy stored. • Q is very difficult to accurately measure. • You can never have too much Q! • The inductor is usually the part with the poorest “Q”, so a lot of creative energy is invested into optimum devices.

Coil Types • The highest “Q” coils seem to be air core. • Many different variations – Spider web, – Basket weave – Honey Comb

• All attempt to reduce capacitance and current crowding to increase Q

Coil Winding Jig Drinking straws fit over ¼” dowels. Comb helps space wires

Litz Wire

• Best wire for high “Q” coils is Litz wire. • Litz is derived from the German word “Litzendraht” meaning woven wire. • Consists of many strands of parallel connected, individually insulated wire woven together in a regular pattern. • Each wire alternates between the middle and the outside of the bundle. • Each wire forced to carry about the same current, minimizing skin effect (the tendency for current to flow along the outside surface of a wire), and loss. • The holy grail of litz wire is made up of 420 to 660 individual strands of 46 AWG wire all twisted together to make a 16-18 AWG wire. • One comparison: A basket wound coil with solid copper wire (~200uH) has a Q of 230 at 1MHz. With Litz wire, it has a Q of over 500!



• In my experience, nothing beats a good 1N34A germanium diode. (Still widely available) • Germanium is good because its barrier height (turn-on voltage) is lower than silicon, and a germanium diode is truly a pointcontact diode (Schottky, not P-N diode), so has low charge storage (and therefore fast switching times). • Specified with very low capacitance, less than 1.0pF. • Main complaint about 1N34A diodes is that they tend to have high and highly variable leakage. • Best solution is to try several, doing A B comparisons and select the best germanium diode in your drawer .

Detector Impedance • Detectors are most efficient when driven with high voltages.

– Detectors are “square law” devices (at low power), output voltage is proportional to square of input voltage.

• Since we have a fixed amount of input power, we need to increase voltage and decrease current applied to the detector (Power=Voltage x Current); in other words increase the detector impedance. • At detector input: use a loose coupler. • At detector output: use a 100kohm microphone transformer to match into the headphones.

Germanium Diodes

Detectors: I-V Curves Diode I-V Curve

1N914 1N34A_Act

Current, Amps










HP Sch 1 HP Sch 2

0 0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Forward Bias


6AL5 3AL5 3AL5+

Detectors: I-V Curves 1N914

Current, Amps

0.1 0.01











HP Sch 1


HP Sch 2

0.000000001 -1.5




Diode Voltage



6AL5 3AL5 3AL5+





Galena Detector

X-Y-Z manipulator

Galena mounted in solder

Audio Transducer

• Best transducers (headphones) for crystal radio operation are “Sound Powered” headphones or “Deck Talkers”. • Developed in WWII for the navy to allow communications between the observers and gunners without the need for external power source. • So sensitive that the pressure of the talkers voice in the microphone is sufficient to drive the headphones of the listener.

Audio Transducer

• An elaborate mechanism balanced armature system) give the sound powered headphones their sensitivity. • Impedance typically around 1000 ohms, much too low for direct use in a crystal set. An impedance matching transformer is essential. • Microphone transformers are excellent choices for matching the impedance of the diode to the headphones.

Final Results • Litz wire basket wound with taps for experimentation. • Series antenna tuner above 650kHz. Below 650kHz, capacitor has to be placed in parallel with the inductor • Ceramic insulated variable capacitors for maximum Q • R-C allows DC to build up, reduces detector loading and reduces distortion on local stations.

Clear Channel Stations

• Most of the distant stations we receive are 50,000 Watt “clear channel” stations. • A clear channel station is a high power American station that shares its frequency with very few other stations • The realization that a station nearly 1000 miles away can be heard in a completely passive crystal radio is amazing

Clear Channel Stations

Stations Logged • • • • • • • • • • • • • • • • • • • • • • • • • •

640 CFYI, Toronto 660 WFAN, New York City 680 CFTR, Toronto 690, Montreal 700 WLW, Cincinati 720 WGN, Chicago 740, Toronto 760 WJR, Detroit 770 WABC, New York City 780 WBBM, Chicago 800 CJAD, Montreal 810 WGY, Schenectady 840 WHAS, Louisville 880 WCBS, New York City 920 WHJJ, Providence 940 CINW, Montreal 990 The Team, Montreal 1000 WMVP, Chicago 1010 CFRB, Toronto 1020 KDKA Pittsburgh 1030 WBZ, Boston 1060 KYW, Philadelphia 1080 WTIC, Hartford 1500 WTOP Washington 1520 WWKB, Buffalo 1560 WQEW, New York Citiy

Top Performers

• Mike Tuggle of Hawaii is one of the top builders of crystal sets. • His set, the Lyonodyne-17 has heard stations in Cuba from his home location in Hawaii! • There are lots of web resources available. This presentation describes my efforts.

Conclusions • Crystal sets appear to be simple, but attention must be paid to all the details. • If you truly understand a crystal radio, you have a good foundation to RF engineering in general.

Experiments with LC circuits

Experiments with LC circuits  part 1 Go to part 2 >> Back to the index. Via some experiments en measurements I want to find out, how we can increase the Q of a LC circuit. Description coils L1, L2,L3 First I made 3 coils (L1,L2 and L3) each with 12.5 meter litzwire (40x0.07mm) on the coils, and 2 leads of 0.25 m. So the wire length is each time 13.0 meter. The coils are spiderweb coils wound on corrugated cardboard formers. The difference between the coils is the internal diameter, and so also the number of turns.

Coil L1: inside diameter: 50mm, coilformer diameter: 120mm, number of turns: 50 Coil L2: inside diameter: 40mm, coilformer diameter: 120mm, number of turns: 55 Coil L3: inside diameter: 100mm, coilformer diameter: 170mm, number of turns: 33.5 Description capacitor C1.

The tuner capacitor I used is shown in the picture above. The maximum capacity is 495 pF. The original version is named C1. Later I made some improvements on this capacitor, like changing the screws and insulation rings, on the picture you see the old screws and insulation rings. After each improvement, the name is changed in C1a, C1b, etc. On the picture you see version C1b. Measurement[05.08.2019 09:46:51]

Experiments with LC circuits

In this measurement I measured the minimum and maximum tuning frequency, and the circuit Q at 600, 900, 1200 and 1500 kHz. measurement F min. LC combination number kHz 1 L1 C1 482 2 L2 C1 480 3 L3 C1 495

F max. Q Q Q Q kHz 600 kHz 900 kHz 1200 kHz 1500 kHz 1710 * * * * 1730 200 129 75 58 1710 200 129 71 58

* = not measured. Conclusion: The minimum frequency of L3 is higher than L1 and L2, this indicates a lower inductance of L3 compared to L1 and L2. The Q is rather low especially at high frequencies.   Improvements on C1 Now I replaced C1 temporary with a air trimmer capacitor with a maximum capacity of about 33 pF, this trimmer I connected to coil L2. The minimum frequency was now 1650 kHz, and the Q was 165 at 1650 kHz. Conclusion: The low Q of measurement 2 and 3 is mainly caused by the (bad) quality of C1. In a tuner capacitor the quality is mainly determined by the kind of insulation between rotor (turnable part) and the stator (non turnable part). In C1 the insulation between the plates is air, and this is a high quality insulation. But there are also insulation parts needed to connect the rotor to the stator to each other, and these also have to be high quality, and also the capacity caused by these insulation parts must be as low as possible. For reducing the capacity between rotor and stator, I replaced the metal screws with nylon screws. The minimum capacity of C1 now drops from 33 pF to 20 pF. This version of the tuner capacitor I call C1a. Next I made this measurement: Measurement F min F max Q Q Q Q LC combination number kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz 4 L2 C1a * 1950 240 225 171 107 Compared with measurement 2 the Q is much higher, especially at higher freqencies. Because the lower minimum capacity of C1a, the maximum frequency of the circuit is also higher. Next I replaced the original insulation rings by selfmade insulation blocks made of polyethylene (PE-UHMW), This version is named: C1b and has a minimum capacity of 14 pF. This also gives a improvement of the Q. Measurement F min F max Q Q Q Q LC combination number kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz 5 L2 C1b 472 2060 300 300 200 166[05.08.2019 09:46:51]

Experiments with LC circuits

Use of other tuner capacitors For the next experiment I replaced C1b by the following tuner capacitors:

C2 390 pF tuner capacitor with silvered plates.

C3 Small 500 pF tuner capacitor. With plastic foil insulation between the plates.   This gave the following results: measurement F min F max Q Q Q Q LC combination number kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz 6 L2 C2 537 2020 300 300 214 195 7 L2 C3 * * 133 128 109 94 Measuring coil L1 and L3 The next measurements are again made with capacitor C1b. Now the capacitor is improved, I want to measure again the differences in Q of coil L1, L2 and L3. L2 was already tested in measurement 5, here are the results for L1 and L3. Measurement F min F max Q Q Q Q LC combination number kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz 8 L1 C1b 473 2050 300 300 200 166 9 L3 C1b 487 2050 300 300 200 166 The Q of the coils L1, L2 and L3 are the same, the Q seems not to be dependent on inside diameter of the coils.   Coilformer made of foam PVC

Coil L4[05.08.2019 09:46:51]

Experiments with LC circuits

Coil L1, L2 and L3 have corrugated cardboard coilformers. This coil (L4) has a coilformer made of white foam PVC, this is PVC with small aircells in it. The foam PVC is 3mm thick. Wirelenght is again 13.0 meter (12.5 m on the coilformer, and two leads of 0.25 m). The wire is also 40x0.07 litzwire. The internal diameter of L4 is 50mm.  

Measurement F min F max Q Q Q Q LC combination number kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz 10 L4 C1b 480 2085 326 310 261 200 Conclusion: the foam PVC coilformer gives a bether Q than the corrugated cardboard former.

Coil L5 Coil L5 has a former made of 3mm foam PVC. There is as much as possible material removed from the former. For the rest it is the same as L4.  

Measurement F min F max Q Q Q Q LC combination number kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz 11 L5 C1b 484 2050 360 346 279 242 So, removing material from the former also has a positive effect on the Q. Go to part 2 >> Back to the index.[05.08.2019 09:46:51]

Experiments with LC circuits

Experiments with LC circuits    part 2 >  Back to the index     The next experiment is made with basket weave coil L6. The tuner capacitor is C1b.

Coil L6. This coil has no coilformer. The wirelength on the coil is 12.5 meter, and two leads of 0.25m. So, the total wirelength is 13.0 m. The inside diameter is about 11 cm. Number of turns: 32. Wire: litz 40x0.07mm The intersections of the wires are glued together

Measurement  F min  F max  Q Q Q Q LC combination  number kHz kHz 600 kHz  900 kHz  1200 kHz  1500 kHz  12 L6 C1b 512 2075 317 340 279 243   In the next experiment the coil is divided over two coilformers. The outside diameter of the coil is now reduced, and the receiver can be build more compact. The distance between the coilformers is adjustable, I made measurements with distances of 10, 20 and 40 mm.

Coil L7 This coil has two coilformers of foam PVC. Each former is wound with 6.25 meter wire, and there are two leads of 0.25 m. Total wirelenght is 13.0 meter. Wire: litz 40x0.07 mm. Number of turns: 29 per former, so total of 58. Inside diameter of the coil: 50 mm. The coil must be wound on both formers in the same direction.   Measurement  F min  F max  Q Q Q Q LC combination  number kHz kHz 600 khz  900 kHz  1200 kHz  1500 kHz  13 14

L7 C1b 10mm distance L7 C1b












224[05.08.2019 09:48:16]

Experiments with LC circuits

20 mm distance 15

L7 C1b 40mm distance







  The next coil has less wire then the coils before. Coil L8 The wirelenght on the former is 6.5 meter, and the two leads are 0.25 meter. Total wirelenght is 7 meter. Wire: litz 40x0.07 mm. Coilformer material: foam PVC. Coil inside diameter: 50mm. Number of turns: 30.   Measurement  F min  F max  Q Q Q Q LC combination  number  kHz kHz 600 kHz  900 kHz  1200 kHz  1500 kHz  16 L8 C1b 816 3490 * 303 287 269 Because of the shorter wirelenght, the minimum frequency is not very low, but the Q at 1200 and 1500 kHz is higher then all coils before. >  Back to the index[05.08.2019 09:48:16]

Experiments with LC circuits

Experiments with LC circuits part 3 > Back to the index The next step in improvement of the LC circuit is the use of litzwire with very much strands. The next coil is made with litz 660x0.04mm (also called 660/46,  660 is the number of strand, the wiresize is 46 AWG = 0.04 mm). Coil  L9 Wirelenght on the coil: 14.5 meter and two leads of 0.25 m. Total wirelenght: 15 meter. Inside coildiameter: 6 cm. Outside coildiameter: 16 cm. (coilformer is 20 cm diameter). Number of windings: 41 Wire: litz 660x0.04mm Coilformer material: 3mm foam PVC Induction: about 175 uH. One measurement is made with capacitor C1b, and one with C2. Measurement  F min  F max  Q Q Q Q LC combination  number kHz kHz 600 kHz  900 kHz  1200 kHz  1500 kHz  17

L9 C1b 537 With 1:100 probe 







L9 C2 With 1:100 probe







Conclusion: C1b gives a higher Q then  C2, this is strange, in  measurement 5 and 6 C2 gives the highest Q. Coil L9 has a lower induction then e.g. coil L5 (F min is higher), though L9 has more wirelenght. The 660x0.04 litz seems to give less induction then the 40x0.07 litz. The Q of L9 is much higher then the coils made with 40x0.07 litz. Until now the Q measurements were made with a 1:100 probe between LC circuit and oscilloscope. The test setup is discribed here as test setup 2. But I found that the testprobe has a negative effect on the Q. In the next measurement I use a self-made FET amplifier between the LC circuit and the oscilloscope. The test setup is described here as test setup 3 The same circuits are now measured again. Measurement number

LC combination

F min F max Q Q Q Q kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz


L9 C1b 538 With FET amplifier 


L9 C2 With FET amplifier 












By using the FET amplifier, the Q increases, especially at high frequencies.[05.08.2019 09:50:37]

Experiments with LC circuits

When measuring high Q circuits, the frequency of the signal generator must be adjusted very accurate. With the sweep signal generator I used this was not easy, so the values of Q were not reliable. Now I replaced the sweep generator by a DDS generator, at which the frequency can be very accurate set. The test setup you will find here as test setup 4. With the use of the DDS generator I measured the Q's again of the same circuits: Measurement number 21 22

LC combination

F min  F max  Q Q Q Q kHz kHz 600 kHz 900 kHz 1200 kHz 1500 kHz

L9 C1b With FET amplifier 539 and DDS generator L9 C2 With FET amplifier 604 and DDS generator







915 (604 kHz)




The Q's in measurement 21 and 22 are mostly lower than in measurement 19 and 20, this is caused by the inaccuracy of measurements until number 20. The measurements 17-18 and 19-20 and 21-22 are all done withe the same LC circuits, only the used test equipment was different. In my opinion measurement 21 and 22 give the most reliable Q values. But the measurements before were also usefull because a increase or decrease of Q could be seen . > Back to the index[05.08.2019 09:50:37]

Experiments with LC circuits

Experiments with LC circuits  part 4 >  Back to the index From tuning capacitor C1b I now removed the insulation rings which keeps the stator on it's place. I found that the used nylon screws gave some dielectric losses which reduces circuit Q. Now I use instead a polyethene block which supports the stator from the underside. In the following drawings this is shown., this version of tuning capacitor I call: C1c.

Tuning capacitor C1b  1= frame of tuning capacitor 2= plastic insulation ring 3= nylon screw 4= polyethene insulation block 5= copper connection bar for stator plates 6= statorplates

Tuning capacitor C1c 1= frame of tuning capacitor  2= copper connection bar for stator plates 3= metal screw 4= polyethene block 5= polyethene bottom plate 6= nylon screw 7= statorplates

The plastic insulation blocks of tuning capacitor C2 are replaced by polyethene blocks (which are the green blocks on the next picture).

Left: C1c  (495 pF). Right: C2a (390 pF).

After these changes, I measured the Q's again, they were increased. The percentages of increase are also mentioned, compared to measurement 21 and 22. Measurement  F min  F max  Q Q Q Q LC combination  number kHz kHz 600 kHz  900 kHz  1200 kHz  1500 kHz[05.08.2019 09:54:31]

Experiments with LC circuits


L9 C1c 



L9 C2a


1072 947 815 658 (+10.7%) (+7.3%) (+19.3%) (+12.8%) 1143 1000 833 632 2400 (+24.9%) (+32.2%) (+46.6%) (+55.3%) (606 kHz)  2349

Now I have drilled a lot of 2 mm holes in the polyethene insulation blocks of tuning capacitor C2a. Hoping that removing insulation material will reduce dielectric losses even more. This version of tuning capacitor is called: C2b. Measurement  F min  F max  Q Q Q Q LC combination  number kHz kHz 600 kHz  900 kHz  1200 kHz  1500 kHz  25

L9 C2b 



1052 (-7.9%)

1000 (0.0%)

875 (+5.0%)

714 (+12.9%)

The percentages mentioned are compared to measurement 24. At 600 kHz there is a decrease in Q, how that comes, I don't know. Maybe there was a measuring error in measurement 24, normally the accuracy of the measured values are I think between +5% and -5%, but maybe this time the error is higher. Or maybe the Q is really reduced at 600 kHz, this is no problem, at low frequencies a Q above 1000 is more than enough. "Tot lering en vermaak"  That's an old Dutch expression which means "for learning and fun". And that's why I made the following two measurements with lower Q coils, often used in crystal receivers. Coil L10 13 meters litzwire 40x0.07mm on a former made of a CD. The shiny aluminium layer is fully removed from the CD. Coil L11 70 turns on a toilet paper roll. Wire: massive 0.8mm enameled copper wire. Wirelength: about 10.5 meters. The windings are not laying nice side by side, because it was used (old) wire with lots of bendings. The used tuning capacitor is C2b. Measurement  F min  F max  Q Q Q Q LC combination  number kHz kHz 600 kHz  900 kHz  1200 kHz  1500 kHz  26 L10 C2b 530 * 358 371 346 304 27 L11 C2b 761 3270  * 211 234 241 * = not measured. The measured values are not bad at all, but keep in mind that a very good tuning capacitor is used. So, a good comparison with measurement 1 to 16 is not possible, also because the test method used now is much better. > Back to the index[05.08.2019 09:54:31]

Experiments with LC circuits[05.08.2019 09:54:31]

Experiments with LC circuits

Experiments with LC circuits  part 5

Back to the index Via measurements I determined the effect on circuit Q, if we place several  materials near the coil of the LC circuit. Test setup 1. First I placed the material near the coil, so the material makes a right angle with the coil windings.

Test setup 1: The material makes a right angle with the coil windings.

The coil is spiderwebcoil  L9    The given distance is measured between the material and the outside winding of the coil. Some materials are measured at several distances. In measurement 28 there is no material placed near the coil, this measurement is used as a 0% reference for the other measurements. This measurement 28 is done some days earlier than the other measurements, maybe building up the test setup again has some influence on measured values. I also measured the frequency shift caused by the material near the coil. frequency distance  shift at (cm) 600 kHz. (kHz) none wood 2 -0.05 wood 5 * wood 10 * cardboard 2

Back to the index[05.08.2019 09:58:35]

Experiments with LC circuits[05.08.2019 09:58:35]

Experiments with LC circuits

Experiments with LC circuits  part 9 > Back to the index In this measurement, the Q is measured with different tuning capacitors.

Tuning capacitor C1c 500 pF With polyethene insulators and copper plates.


Tuning capacitor C4  2x 365 pF Brand: Hopt. With ceramic insulators and aluminium plates.


Tuning capacitor C5  2x 500 pF From a old tube radio. With ceramic insulators and copper plates.

The used coil (L12a) is coil L12 with the last winding removed. The induction of L12a is about 169 uH. Coil L12a is mounted in my "antenna unit 1" (description comes later), in the antenna unit 1 there are two tuning capacitors placed near the coil, this can give some reduction in Q compared to measurement 74. In measurement 84, I placed back two sets of old insulation rings on tuning capacitor C1c (these are the rings removed in measurement 5 ). Original there were 4 sets of insulation rings on C1, but I couldn't replace the other two set's without dismantling the whole antenna unit 1, and this was too much work.[05.08.2019 10:02:01]

Experiments with LC circuits

With tuning capacitor C5, one measurement is made with one 500 pf section, and one with the two 500 pF section parallel. Measurement  number

LC combination


L12a C1c


F min F max Q 600 kHz  Q900 kHz Q 1200 kHz Q 1500 khz kHz kHz 550






L12a C1c 546 with old insulation rings







L12a C4 (2x365 pF)








L12a C5 one 500 pF section








L12a C5 2x 500 pF parallel







Conclusions:  Tuning capacitor C1c and tuning capacitor C4 almost give the same circuit Q. Placing back the old insulation rings on tuning capacitor C1c gives a large reduction in Q. Here we see the importance of good quality insulators in tuning capacitors The old tuning capacitor C5 gives a lower Q than C1c and C4, maybe this is caused by: - less quality of the ceramic insulators - contact resistance between rotor and frame of the capacitor - oxidation of the plates. > Back to the index[05.08.2019 10:02:01]

Experiments with LC circuits

Experiments with LC circuits   part 10

Back to the index[05.08.2019 09:59:28]

FET amplifier for measuring LC circuits

FET amplifier for measuring LC circuits. Back to the index

Version 1

Figure 1: This amplifier can be used for measurements on LC circuits. The metal lid is removed for the photo.

The input of the amplifier is connected to the LC circuit. The amplifiers input has the following properties: a- High input resistance. b- Low input capacitance (about 1.4 pF). c- Low dielectric losses, because of the use of high quality insulation materials. Because of this properties, the LC circuit is almost not loaded by the amplifier, so the Q will almost not reduce. The output resistance of the amplifier is 50 Ohm. If the amplifier output is not loaded, for instance it is connected to a 1 Mega-Ohm oscilloscope input, then the amplifier gain is 1x, and the maximum output voltage is 8 Volt peak-peak. If the output is loaded with 50 Ohm, then the gain is 0.5x and the maximal output voltage is 4 Volt peak-peak. The gain is constant between 10 kHz and (at least) 10 MHz. The amplifier output can e.g. be connected to: - An oscilloscope - RF voltmeter - RF wattmeter - Diode detector with voltmeter

Figure 2: Circuit diagram of the FET amplifier (see also the updates at the bottom of this page)   Circuit description: The input signal enters the amplifier via a 0.3 pF input capacitor, together with the input capacitance of the FET (T1) this forms a voltage divider, the input signal is attenuated 17 times by this divider.[05.08.2019 09:53:16]

FET amplifier for measuring LC circuits

The 0.3 pF input capacitor is self-made of two copperplates of 1 square cm at a distance of 3 mm. By changing the distance between the plates we can adjust the gain of the amplifier. The plates must have at least 1 cm distance from the surrounding grounded box. The input signal enters the box via a 1mm copperwire, through a 10 mm hole in the box. The wire is supported by a piece of polyethene, which is fixed with nylon screws. The input amplifier (T1) is screened from the rest of the circuit. Between the gate (input) of T1 and ground there is a 20 M.Ohm resistor. But the input resistance of the amplifier is much higher then 20 M.Ohm, in theorie even 17² times higher  (so, 5780 M.Ohm), this is because over the 20 M.Ohm resistor is only 1/17th part of the input voltage. In practice the input resistance will be lower then 5780 M.Ohm because of dielectric losses e.g. in the gate of the FET. Transistor T2 is set to a gain of 17 times. Or to be more precise -17 times, because this transistor is inverting the signal, but this is for the rest not important. On the collector of T2 the amplitude is the same as the input amplitude of the amplifier. The DC voltage on the collector of T2 must be about 6 to 7 Volt, if it is outside this range, adjust the value of the 1K2 resistor or 10K resistor at the base of T2. T2 (BFR92A) is a very fast transistor (up to 5GHz) in SMD case, because of the high speed, T2 can give parasitic oscillation. If this happens you better use a slower transistor like the BF199 (up to 500 MHz). T3 and T4 form a buffer amplifier with a gain of 1x. The amplifier is capable of driving a 50 Ohm load.

Amplifier version 2 The same amplifier is build once again, but with regard to version 1 with the following modifications: - An aluminium case instead of a tinplate case, this gives less influence on circuit Q. - The hole in the case for the input pin is increased to 13 mm (was 10 mm). - The support for the input pin is now made of  polypropylene (was polyethene with a nylon screw). - The support for the first capacitor plate is now made of polypropylene (was epoxy PCB material). By means of these modifications I tried to reduce the dielectric losses in the amplifier.

Figure 3: the amplifier version 2.  In an aluminium case of 112x62x30 mm.[05.08.2019 09:53:16]

FET amplifier for measuring LC circuits

Figure 4.[05.08.2019 09:53:16]

FET amplifier for measuring LC circuits

Figure 5: detail of the input stage.[05.08.2019 09:53:16]

FET amplifier for measuring LC circuits

Figure 6. In the next measurements I measured with both amplifiers the Q of  detectorunit1. Also the Q is measured with both amplifiers parallel connected to the LC circuit. The diode was in these measurements disconnected from the LC circuit. When measuring "version 1",  I laid an aluminium plate on the amplifier, to increase circuit Q (see also lctest6 measurement 63). Amplifier version Version 1 Version 2 Version 1 and version 2 parallel

Q Q Q Q 600 kHz 900 kHz 1200 kHz 1500 kHz 1111 1046 889 731 Q factor of detector unit 1 Measured with different measuring amplifiers. 1111 1125 952 802 1090




Conclusions: - Amplifier "version 2" gives a higher Q value, so version 2 gives less load (higher resistance) to the LC circuit. - De Q factor with "version 1" and "version 2" parallel is almost equal to the Q measured with only "amplifier version 1". This indicates that the input resistance (at that frequency) of "version 2" is almost infinite high, at least high enough to have almost no influence on measured Q. Update 1 Here a part of the circuit diagram of figure 2:[05.08.2019 09:53:16]

FET amplifier for measuring LC circuits

Figure 7:    12 V power circuit for the FET amplifier. The practice has shown that the input diode (BYV10-40), easily gets defective when connecting the supply voltage (the diode gets an internal short-circuit). This may be caused by static charge exceeding the maximum reverse voltage of the diode. Or by too high peak current when charging the 100 μF capacitor at the input of the 7812. To solve both problems, here some modifications, in figure 7 drawn in red. - At the power supply input, a 100 nF capacitor to ground is added (removes static charge). - The value of the 100 μF capacitor is reduces to 1 μF (reduces peak current at power-on) The current consumption of the FET amplifier, inclusive 7812 voltage regulator is about 43 mA. Update 2 When using the 7812 voltage regulator, at least 15 volt input voltage is needed. This voltage can well be supplied by a non-stabilized 12 V means-adaptor, these adaptors deliver 12 V at maximum supply current, but at light loads much more voltage, for instance about 17 volt DC. If you want to power the circuit also from a 12V rechargeable battery, you however have not so much voltage available. Depending on the charging condition of the battery, 12 to 13.8 volt. By using a low-drop regulator it is possible to get a 12 volt stabilized voltage at these low battery voltages. The reasons for powering the circuit from a battery can be: - For doing measurements in the field, where no means voltage is available. - To prevent interference from the means. - To prevent an unintended connection between circuit and earth, via the internal capacitance in the means adaptor.

Figure 8: power circuit for the FET amplifier with low-drop voltage regulator. As low-drop voltage regulator I used the LM2940T-12 (LM2940_datasheet) , because I had one laying around. You can also use the LM2940CT-12, which is a more common type. The minimum voltage between input and output is depending on load current. But with the 40 mA the FET amplifier uses, there is at least 50 mV necessary between input and output. So at only 12.05 volt battery voltage, we still have a stabilized 12 Volt output voltage. When the battery voltage drops below 12 volt, the output of the LM2940 will follow at 50 mV below that. If the voltage regulator has enough cooling, the input voltage may be increased to a maximum of about 29 volt. Above 30 volt input voltage,  the regulator is switching off the output voltage. The FET amplifier inclusive LM2940T-12 uses about 50 mA. One nice property of this voltage regulator is, that it can withstand negative input voltages. So if you accidentally connect the input voltage with wrong polarity, it can do no harm. Therefore there is no need for a diode to protect the voltage regulator for negative input voltages. The capacitor at the output of the LM2940T-12 must have an internal resistance (ESR value) between 0.1 Ω and 1 Ω. The 47 μF/25V capacitor I used, has a measured resistance value of 0.3 Ω, so it was useable.[05.08.2019 09:53:16]

FET amplifier for measuring LC circuits

Figure 9:  this picture shows the frequency response of the amplifier (version 2) between 0 and 50 MHz. The - 3 dB point is at 14 MHz. Back to the index[05.08.2019 09:53:16]

.(9,1¶6:(%685)(5 +$1'%22., )25&5