Communications monitoring

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Communications monitoring

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communications Monitoring


communications Monitoring ROBERT B. GROVE

[]] HAYDEN BOOK COMPANY, INC. Rochelle Park, New Jersey

Library of Congress Cataloging in Publication Data Grove, Robert B Communications monitoring. I ncludes index. 1. Radio-Monitoring receivers- Amateurs' manuals. I. Titl e. TK9956.G68 621.3841 '51 79-1894 1 ISBN 0-8104-0894-0

Copyright © 1979 by HAYDEN BOOK COMPANY, INC. A ll rights reserved. No part of this book may be reprinted, or reproduced, or utilized in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and record ing, or in any info rmation storage and retrieval system, without permission in writing from the Publ isher. Printed in the United States of America









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Preface No other armchair hobby can provide the endless hours of enjoyment, the foreign intrigue, the vicarious satisfaction of eavesdropping, and the intellectual fulfillment that monitoring the radio spectrum can provide. Espionage, smuggling, undercover intelligence, military maneuvers, propaganda, life-and-death emergencies-all of these can be heard .. . if you know when and where to listen! Beside making you aware and alert, hobby radio listening can also be a challenge. What sort of receiver will you need? What kind of antenna should you use? What are the best times for you to listen to different frequency ranges? These and many other questions will confront you, the listening enthusiast. This book was written to help you meet that challenge! Robert B. Grove

con1en1s Preface Introduction 1. Users of the Spectrum



Modes of Transmission 5 Tone Paging 5 Telemetry 6 Digital Encoding 6 Voice Encoding 7 " Bugging" Devices 7 2. Receivers


Buying Used Receivers 12 Listening Below the Broadcast Band 13 Broadcast-Band DX'ing 16 Shortwave 18 VHF/UHF Receiving Equipment 18 Monitors 18 Scanners 20 Servicing 23 Crystals 23 Sensitivity 24 Selectivity 24 Converters 25 Power Requirements 25 3. Antennas Shortwave Antennas 28 Dipole Antennas 29 Vertical Antennas 32


VHF and UHF 33 Mounting 34 Choosing the Antenna 34 Mobile Operation 3 5 Preamplifiers 3 5 Transmission Line at VHF/UHF 36 Grounding 3 7 Directional Antennas 3 7 A Directional Beam You Can Build 3 7 Transmission Lines for Shortwave Reception 41 Interference 41 4. Listening Hints


Publications 43 Clubs 44 When to Listen 44 Logging 45 Accessories 4 5 Listening and the Law 46 5. Projects Section Ground-Plane Antenna for VHF/UHF Projects 50 Optimize Your Antenna with This All-Band Transmatch 53 Erase Signal Interference with an Antenna Wavetrap 57 A Wide-Tuning-Range Trap Filter for General Coverage Receivers 5 8 An Inexpensive Adjustable Power Supply for Experimenter Projects 61 Build This Professional 0- to 24-V Regulated Power Supply for Your Test Bench 64 88- to 136-MHz Receiver for FM Broadcast and Aircraft 66 Converting an AM/FM Radio to An Aircraft Receiver 70


A Pocket Police Receiver from a Weather Radio 74 Making a Good Portable Better: Improvements for the Patrolman CB-6 77 A VLF Converter for Your Shortwave Receiver 88 Direct-Conversion VLF Receiver 92 Listen to Fish Talk with This Hydronics Receiver 96 Build This 100-kHz Crystal Calibrator for Frequency Spotting 98 High-Performance Audio Amplifier to Boost Receiver Volume 102 A Speaker Power Amplifier for Noisy Locations 104 An Audio Filter for Clearer Reception 107 Build This Voice Decoder and Hear Scrambled Voice Messages 109 Index


lnlroduclion The United States is the largest user of radio equipment in the world. There are over 20 million CB sets in use alone. Other nongovemment and government two-way radios comprise additional millions. During the 1930s and 1940s, many household radios had shortwave coverage in addition to the standard broadcast band; listeners could tune in on police calls, which were slightly higher in frequency (around the 2-MHz range) than the commercial broadcasters. Except for communications networks among high-powered base stations, mobile range was very limited. Antennas were too small at those frequencies, equipment was cumbersome and less efficient, battery drain was severe, and the AM mode was highly susceptible to ignition noise. Gradually, the state of the art has evolved into a highly reliable extended-range system, with repeaters, compact FM transceivers, mobile teletype, and other highly sophisticated means to informational exchange. The radio frequencies used for these services now are much higher- hundreds of times higher-than those of the first mobile two-way radios. These VHF (very high frequency) and UHF (ultra high frequency) land mobile services between 150 and 1000 MHz are growing explosively, as we shall see later. With solid-state integrated circuits, equipment is now of better quality a.nd yet costs less. Much of this commercial technology is also available to the consumer in hobby-type transceivers and receivers (see Fig. A).



Fig. A

Remember that most of what you hear is considered private and is protected by law (see Chap. 4 , " Listening and the Law").

1 users ot the Spectrum The vast majority of land mobile users are found in three frequency ranges: 30- 50 MHz (VHF-FM low band), 150-174 MHz (VHF high band), and 450- 512 MHz (UHF). The newest region of the communications spectrum to be made available to the land mobile services is the 806-960 MHz range. It is not found on any consumer monitors available at this writing and is only slowly growing in acceptance within the industry because of its slightly reduced reliable range and susceptibility to signal flutter. Because of the vulnerability of the older 30-50 MHz range to long-distance "skip" interference and electrical noise (just as in the adjacent 27-MHz citizens band) , more and more two-way users are abandoning these frequencies in favor of the higher frequencies. There are still many state and military agencies to be found using them, however, especially in hilly terrain or when considerable distances must be covered. By far, the most commonly monitored frequency ranges in the VHF and UHF bands (Fig. 1-1) are 30-50 MHz; 108136 MHz (VHF aircraft band; AM, not FM); 150-174 MHz (VHF high band, including the popular 144- 148 MHz amateur 2-meter band); 450-470 MHz (the original UHF band); and 470-512 MHz (the newer UHF "T-band," taken from 3







7- 13

Fig . 1-1

Major users of the VHF /UHF spectrum



20-69 -



the lower UHF television frequencies and growing rapidly in larger metropolitan areas). FCC;-allocated channels are normally spaced at intervals of 15 kHz (high band), 20 kHz (low band), 25 kHz (UHF), or 50 kHz (aircraft band). IRAC frequently spaces Federal Government allocations at 12.5-kHz intervals ("splinter channels") , as does the FCC in some metropolitan areas. In the United States, two agencies are responsible for frequency allocations: The Federal Communications Commission (FCC) regulates non-Federal Government users (commercial broadcast, aeronautical, maritime, public safety, amateur, citizens band , business and industrial, transportation, mobile telephone, and local government). The Interdepartmental Radio Advisory Committee (IRAC), a branch of the Department of Commerce Office of Telecommunications Policy (OTP), assigns all Federal Government users (Defense, Interior, Agriculture, Justice, Treasury, State, Commerce, NASA,



DOE, FCC, NSA, TVA, HEW, Postal Service, VA, NTIA, and others). Hobby listeners refer to all one-way transmissions intended for public listening as "broadcasts" and all other communications as "utilities"; several examples are listed in Chap. 2 in the "Shortwave" section. Modes of Transmission In the early days of radio broadcasting and two-way communications, all voice transmissions were by amplitude modulation (AM). Now, virtually all VHF and UHF voice communications use the frequency-modulation (FM) mode. The only significant holdout is the aeronautical service. All aircraft and tower VHF (108-136 MHz) and military UHF(225-400 MHz)voice contacts are made on AM. In addition to voice communications, the VHF/ UHF listener will occasionally encounter tone paging "beeps," telemetry, data bursts from digital encoding (like police mobile teletype), and voice encoding. Tone Paging It is difficult to tune across any of the land mobile bands without corning across the melodic "beeps" of tone paging. It is possible for more than two million subscribers, each wearing a pocket-paging receiver, to be individually paged from one transmitter operated by a Radio Common Carrier! These high-capacity systems are far more sophisticated than is the circuitry needed to activate the simpler two- and five-tone sequential pagers heard broadcasting their musical pitches d1roughout the VHF and UHF frequency ranges. The most common type of paging incorporates the twotone transmissions. When a pager detects the proper two tones in sequence (as determined by a highly selective tone filter in its audio squelch circuitry), it activates the audio circuitry, permitting the user to hear either the tone, a subsequent voice message, or both. Virtually all major industries and agencies use some form of paging system when contact with their personnel is urgent.



Telemetry Not all electronic "beeps" intercepted on the communications frequencies are pagers, however; telemetry also uses discretetone transmission for informational transmission. While pagers use their tones to open a squelch selectively on a receiver, telemetry is a one-way transmission of data to a receiver; the data is encoded as a series of pulsed tones. Uses of telemetry systems vary from hydrological water-level information in flood control to sophisticated patient-monitoring in hospitals. Blood pressure, heartbeat, respiration, and many other vital signs are continuously monitored and broadcast to a central receiving position where an attendant will be alerted to any variation outside of limits programmed by medical personnel. While higher-powered hydrological data may be transmitted many miles to its receiving stations, medical telemetry is normally confined to low-power, short-range, in-hospital use. One exception is the cardio-telemetry transmissions made by paramedical personnel on a rescue call. These channels are assigned by the FCC every 25 kHz from 463.000 MHz through 463.175 MHz.

Digital Encoding Another form of data transmission is the raucous, raspy burst of digitally encoded information exchanged between the data terminals that supplement many police agency communications. Video terminals mounted both in police cars and police stations utilize the same frequency bands provided for voice communications; in large metropolitan areas, one channel allocated to the police agency may be reserved exclusively for the transmission of such encoded information as license tag numbers, vehicle registrations, dates of birth, and so forth. When properly utilized, these data terminals can provide fast and reliable informational exchange that would normally be very time-consuming as voice traffic.



Voice Encoding Because of the rapidly increasing number of monitors in use, security-conscious agencies use various kinds of encoding. Most commonly used is the "ten code." Many law-enforcement agencies use the APCO "Ten Code" (Fig. 1-2). Some municipalities (like Miami, Florida) use portions of the old telegraph Q-code. Still others fabricate their own codes to discourage monitoring ; this practice is not common because of the confusion that could occur when police officers transfer from one department to another. When the ultimate in secure voice transmission is required, as during surveillance , speech-scrambling techniques are employed . The voice is electronically altered to an unintelligible garble that can be unscrambled only by a similar device. Most scramblers use simple speech inversion, as more complicated techniques become increasingly more difficult to adjust properly. Commercial descramblers, similar to the one shown in Fig. 1-3, are available at reasonable cost from companies like Krystal Kits (Box 445 , Bentonville, AR 72712) and Don Nobles (Box 265B, Hot Springs, AR 71901 ). A typical descrambler circuit is presented in the Projects Section of this book. "Bugging" Devices During the 19 50s and 1960s, the use of clandestine surveillance electronics was widespread. There was no control beyond good taste, and that was rare! Employers bugged employees, employees bugged their bosses, jealous wives bugged suspect husbands, and on and on. But then came the passage of a bill from Congress, the so-called "Omnibus Act." It became illegal to use such clandestine devices to invade the privacy of anyone for any reason unless so authorized by a judge in his jurisdiction only, and then only after the applicant had submitted the reason for the bug, the period of time for its intended use, and the sort of information that it



10-0 -Caution 10-1 - Unable copy - change location 10-2 -Signal good 10-3 -Stop transmitting 10-4 - Acknowledgement (OK) 10-5 - Relay 10-6 - Busy-stand by unless urgent 10-7 - Out of service 10-8 - In service 10-9 - Repeat 10-10-Fight in progress 10-11 -Dog case 10-12- Stand by (Stop) 10-13- Weather-road report 10-14- Prowler report 10-15-Civil disturbance 10-16- Domestic problem 10-17-Meet complainant 10-18- Complete assignment quickly 10-19- Return to ... 10-20- Location 10-21-Call telephone 10-22 - Disregard 10-23-Arrived at scene 10-24- Assignment completed 10-25- Report in person (meet) ... 10-26- Detaining subject, expedite 10-27-( Drivers) Iicense information 10-28- V ehicle registration information 10-29-Check record for wanted 10-30-ll legal use of radio 10..31 -Crime in progress 10-32-Man with gun 10-33- EM ERG ENCY 10-34- Riot 10-35-Major crime alert 10-36 - Correct time 10-37-( Investigate) suspicious vehicle 10-38- Stopping suspicious vehicle 10-39- Urgent-use I ight, siren 10-40-Silent run- no light, siren 10-41 - Beginn ing tour of duty 10-42- Ending tour of duty 10-43- lnformation 10-44- Request permission to leave patrol ...for ... 10-45- Animal carcass in ... lane at ... 10-46- Assist motorist 10-47- Emergency road repairs needed 10-48- Traffic standard needs repairs 10-49- Traffic l ight out at ...

Fig. 1-2

10-50-Accident (F, Pl, PD) 10-51-Wrecker needed 10-52-Ambulance needed 10-53- Road blocked at. .. 10-54- Livestock on highway 10-55- lntoxicated driver 10-56- 1ntoxicated pedestrian 10-57-Hit and run (F , Pl, PD) 10-58- D irect traffic 10-59.:....convoy or escort 10-60-Squad in vicinity 10-61-Personnel in area 10-62-Reply to message 10-63-Prepare make written copy 10-64-Message for local delivery 10-65-Net message assignment 10-66- Message cancellation 10-67- Clear for net message 10-68- Dispatch information 10-69- Message received 10-70- Fire alarm 10-7 1-Advise nature of fire 10-72- Report progress on fire 10-73 - Smoke alert 10-74- Negative 10-75- ln contact with 10-76-En route 10-77- ETA (Estimated Time Arrival) 10-78-Need assist ance 10-79- Notify coroner 10-80-Chase in progress 10-81 - Breatherlizer report 10-82-Reserve lodging 10-83- Work school xi ng at... 10-84-lf meeting ...advise T 10-85-Delayed due to ... 10-86- 0fficer/ operator on duty 10-87- Pickup/ distribute checks 10-88-Advise present telephone# of ... 10-89- Bomb threat 10-90-Bank alarm at ... 10-91-Pick up prisoner/subject 10-92-lmproperly parked vehicle 10-93-Blockade 10-94- Drag racing 10-95- Prisoner/subject in custody 10-96- Mental subject 10-97- Check (test) signal 10-98- Prison/jail break 10-99-Records indicat e wanted or stolen

The APCO " Ten Code"





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Fig. 1-3 Decoders for listening to scrambled voice messages (manufacturers include Don Nobles-at top-and Krystal Kits - at bottom)

was hoped to provide. Needless to say, this act put quite a legal damper on both legitimate and not-so-legitimate eavesdropping! Although this tough bill should have severely restricted the proliferation of these clever little transmitters, it did not. They are still sold in popular magazines as wireless babysitters, wireless microphones, and wireless broadcasters. While the real intent is obvious, the clever promoter protects himself legally. In addition, although a court order is required by law for an agency to plant a monitoring device, only a minority of operations follow that dictum. Technically,information obtained without the court order is inadmissible as evidence; but in fact, information of a criminal nature so intercepted provides law-enforcement officers with enough background to proceed with other av.enues of prosecution. Additional bugging operations may be authorized by the courts to enable legitimate introduction of evidence at a trial.



All electronic surveillance devices may be categorized according to their two basic technologies: remote microphones and radio transmitters. Remote microphones may include any wired device (parabolic mikes, shotgun mikes, spike mikes, etc.); radio transmitters are of far greater interest to our discussion and will be covered in more detail here. If the movement of a suspect's vehicle (car, plane, or boat} is of great interest, a "bumper beeper" may be called into use. This magnetically attached transmitter is essentially a homing beacon; it sends out a short-pulse radio signal approximately once every second or so. The agent may use two phased whip antennas on his car or plane in- order to determine whether the suspect is still dead ahead, or whether he has taken a turn. Two receiving stations may compare crossbearings to determine the exact location of the target. Most tailing transmitters operate in the 30-50 MHz low band, or 150-174 MHz high band. Body bugs are worn by undercover agents to enable other agents who are in on the operation to monitor conversations. Body bugs, which are frequently taped unobtrusively to the agent's side, transmit a few hundred feet at most. The room bug is the one most likely to be encountered in a metropolitan area, especially if you live in a large apartment complex, or near a hotel or motel. Although normally of very low power, a device planted on an outside wall may radiate its tiny signal many hundreds of feet. Most bugs are intentionally short-range; accidental interception is less likely and battery drain is reduced. Some bugs never need batteries, such as those made to resemble wall sockets (and actually use the ac lines for power) and telephone taps (powered by telephone current). Some exotic bugs may be powered by solar light, laser beams, and microwave signals. It is even possible to capture enough of the signal voltage from a nearby TV or radio broadcasting station to power a bug!



With all the publicity surrounding famous "bugging" incidents, what is the possibility of intercepting an active bug? It is quite possible with the proper approach. Common bugging frequencies are near 39, 49, 89, 109, and 15 5 through 17 5 MHz. Thus, most bugs may be readily discovered by the use of a multiband VHF portable radio. It is impossible to predict where bugs will be most likely in use, but motels and apartment complexes are good hunting grounds. Naturally, even the house next door could be the target of some remote surveillance. If you do detect a working bug, remember that it could be providing legitimate evidence for an important criminal investigation; don't be in too much of a hurry to tip off the "target." Naturally, no one would be bugging your own home or office ... would he?

2 Receivers Buying Used Receivers Getting started in shortwave listening is not particularly difficult or expensive. Used receivers are available at a fraction of their original costs (usually about half) and can be found advertised in the classified sections of hobby magazines, amateur radio subscriptions, and local newspapers. They are also often for sale , reconditioned, at amateur radio supply stores in the larger metropolitan areas (see Fig. 2-1). If you find what appears to be a good buy, a few helpful hints are in order before closing the sale: 1. Look it over, inside and out. Does it show signs of abuse, abnormal wear, corrosion, repairs, modifications? Does it have a "cleaned and painted for fast resale" look? Does its age render it obsolete by today's standards? 2. Examine its controls. Does it have an S-meter, selectivity control, RF gain (sensitivity) control, noise limiter? If so, do they still work? On tuneables , does the dial cord work smoothly without slipping? 3. Try it out. With only a few feet of wire attached to the antenna terminal, does it readily pick up stations such as 27-MHz CB? With the BFO on, and a station tuned in so that a whistle is heard, does the whistle remain at a constant pitch without drifting even when the radio is gently tapped? Are there noisy or erratic controls and switches (especially the band switch on multiband radios)? Circuit 12



Fig. 2-1 High-school communications center built around used equipment available locally and through mail-order deale rs

modifications and add-ons may reveal destructive tampering, and misalignment may result in poor sensitivity, selectivity, or distorted audio. And remember that a removed or altered serial number may indicate stolen property! Listening Below the Broadcast Band If the prospective listener thumbs through a catalog of radio receiving equipment, he will notice the conspicupus absence of receiving equipment built for the low-frequency bands, 10- 500 kHz (see Fig. 2-2). Admittedly, the greatest variety of transmissions will be found in the HF (high-frequency) spectrum (3-30 MHz), and more drama is found at VHF and UHF (30-512 MHz) , but the basement band should not be counted out. European broadcast stations, aeronautical weather broadcasts and beacons, maritime messages to shore, and military communications abound in this obscure portion of the radio spectrum below 500 kHz.






Fig. 2-2

Major users of the lowest frequencies



At this writing, one major manufacturer (Palomar Engineers, Box 455, Escondido, CA 92025) offers a converter to be used in conjunction with a shortwave receiver (or transceiver). The Palomar VLF converter (Fig. 2-3) electronically converts the entire 10-500 kHz spectrum to 3 .5--4.0 MHz (as shown in the block diagram of Fig. 2-4), where it is tuned in on a conventional shortwave receiver. If the receiver has good selectivity, frequencies as low as 5 kHz are readily copied with this excellent converter. Alternatively, the experimenter may wish to construct a VLF converter of his own. Such a circuit is described in the Projects Section of this book. For the more ambitious craftsman, a direct-conversion VLF receiver project is included. Occasionally, military surplus radios turn up on the used market capable of tuning in on this low frequency range. For the most part, these radios are very old, bulky, and in need of maintenance; parts are often difficult (if not impossible) to find.



Fig. 2·3 The Palomar VLF converter, providing 10- to 500-kHz reception when used with a 3.5· to 4-MHz receiver or transceiver

Another VLF receiver possibility (shown in Fig. 2-5) is known as the " frequency selective voltmeter. " Originally made to tune individual signals multiplexed on common-carrier services, most of these units are actually VLF receivers ; they turn up occasionally as used commercial surplus, usually in the $100 range. Make sure that the prospective receiver is capable of CW reception, or its use will be limited to the 150-400 kHz AM range.


10 TO 500- kHz R. F. AMPLIFIER 3.51 -4 MHz TO RECEIVER


Fig. 2 -4

Bloc k diagram of Palomar VL F convert er



Fig. 2-5 Frequency-selective voltmeters l ike this old Rycom are actually VLF receivers

For effective low-frequency monitoring, a few additional operating hints are in order:

1. Night-time reception is best; 2. Although a random 50-ft horizontal wire will work, directional loops are preferred in order to eliminate noise interference; 3. All transmissions below 150 kHz are nonvocal and normally unmodulated (teletype, CW, facsimile, beacons, etc.); 4. Since AM broadcast-band overload interference is common, antenna wavetraps or low-pass filters are recommended, especially near metropolitan areas. Examples of effective wavetrap circuits are described in the Projects Section. Broadcast-Band DX'ing One hardy group of radio hobbyists is composed of BCL'sbroadcast listeners; they listen late at night, when long-dis-



tance propagation is favorable, for world-wide broadcast stations in the medium frequencies, 540-1600 kHz. Patience and persistence are necessary since channelization plans place many stations on the same frequen cies. Naturally, closer stations will obliterate the elusive weaker signals, and directional loop antennas are often home-constructed to null out these stations , as shown in Fig. 2-6. Receivers used for broadcast-band DX 'ing are shortwave communications receivers that include the broadcast band. Older receivers (Hammarlund, Hallicrafters, National, and even military surplus) are popular because of their low cost and excellent performance in the lower frequency ranges. Often the BCL combines his broadcast-band enthusiasm with other areas of the spectrum in which commercial and noncommercial broadcasting are prevalent: 150-400 kHz, shortwave , FM broadcast band, and TV channels. Clubs abound that support these activities, holding regular meetings and conventions and comparing QSL cards (confirmations of reception from broadcast ing stations) and photographs of TV screens displaying call-sign identifications of distant stations. Typical of these clubs is the Worldwide TV/ FM DX Association. Bulletins about such clubs and their activities are published periodically in various popular hobby radio magazines available at newsstands .

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