Build Your Own Low-Power Transmitters Projects for the Electronics Experimenter This Page Intentionally Left Blank Build Your Own Low-Power Transmitters Projects for the Electronics Experimenter Rudolf F. Graf William Sheets Boston Oxford Auckland Johannesburg Melbourne New Delhi Newnes is an imprint of Butterworth–Heinemann. Copyright © 2001 Rudolf F. Graf and William Sheets A member of the Reed Elsevier group All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or trans- mitted in any form or by any means, electronic, mechanical, photocopying, record- ing, or otherwise, without the prior written permission of the publisher. Recognizing the importance of preserving what has been written, Butterworth– Heinemann prints its books on acid-free paper whenever possible. Butterworth–Heinemann supports the efforts of American Forests and the Global ReLeaf program in its campaign for the betterment of trees, forests, and our environment. Library of Congress Cataloging-in-Publication Data Graf, Rudolf F. Build your own low-power transmitters : projects for the electronics experimenter / Rudolf F. Graf, William Sheets. p. cm. ISBN 0-7506-7244-7 (alk. Paper) 1. Radio—Transmitters and transmission—Design and construction— Amateurs’ manuals. 2. Low voltage systems—Designs and construction— Amateurs’ manuals. I. Sheets, William. II. Title. TK6561 .G67 2001 621 .384’131—dc21 2001030550 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Butterworth–Heinemann 225 Wildwood Avenue Woburn, MA 01801-2041 Tel: 781-904-2500 Fax: 781-904-2620 For information on all Newnes publications available, contact our World Wide Web home page at: http://www.newnespress.com. 10 9 8 7 6 5 4 3 2 1 Printed in the United States of America In appreciation of their patience and understanding during the preparation of the manuscript, we are pleased to dedicate this book to our wives Bettina and Cindy. This Page Intentionally Left Blank Contents Preface xi 1. Low-Power Transmitters, General 1 Basic Oscillator 2 Master Oscillator–Power Amplifier 4 Heterodyne Mixer–Power Amplifier 4 2. Basic Building Blocks 9 Oscillators 9 Amplifiers 13 Multipliers 14 Modulators 16 Frequency Synthesizer (PLL) Circuits 19 3. Simple Low-Power Transmitters for Experimenters 23 Wireless Microphone 23 Baby Monitor 25 Room “Bug” 26 Telephone Line “Bug” 27 AM Transmitter 28 4. 50 mW VFO-Controlled AM Transmitter for 530-1710 kHz 31 Parts List 34 5. PLL Synthesized AM Transmitter for 530-1710 kHz 35 Parts List 49 DIP Switch Settings 50 Filter Settings 50 Programming 51 DIP Switch S1 Frequency Settings 51 Calculation of the Binary Code for Frequency 52 6. VFO Controlled FM Monaural Transmitter for 88-108 MHz 55 7. Basic FM Stereo Signal Generation Techniques 61 vii Contents 8. PLL Synthesized FM Stereo Transmitter for 88-108 MHz 69 Circuit Operation 71 Construction Procedure 78 Test and Setup Procedure 81 Packaging Considerations 84 Frequency Programming 85 Applications 86 Operation Outside the United States 88 Frequency Programming Chart 88 Parts List 91 9. Microprocessor-Controlled FM Stereo Transmitter for 88-108 MHz 93 MPX2000 Theory of Operation 93 MPX2000 Circuitry 93 Construction of the MPX2000 101 PC Board Assembly 101 Audio and MPX Generator Checkout 105 Voltage Settings and Display Assembly 106 Microcontroller and Logic 107 PLL and RF Section 107 Final Test and Setup 109 Packaging 110 Antennas 112 Parts List 112 10. 20 mW Low-Power TV Transmitter 117 11. 0.5-Watt TV Transmitter for R/C Vehicles 121 Parts List 129 12. 2-Watt TV Transmitter for R/C and Amateur TV for 440 MHz 131 General Description 131 Circuit Operation 132 Construction Procedures 136 Tuneup Procedure 139 Parts List 144 13. 1-Watt TV Transmitters for 902-928 MHz and 1240-1300 MHz 147 General Description 147 Circuit Operation 148 Construction Procedures 152 Tuneup Procedure 155 Parts List 160 14. Experimental 20 mW 915 MHz PLL FM TV Transmitter 163 viii Contents 15. Receiving Converters and IF Systems for Low-Power ATV Transmitters 171 Video IF Systems for Use with Downconverters 185 Theory of Operation 188 IF44 and IF66 188 IF70 FM TV 194 Tuneup 206 IF44 and IF66 206 IF70 FM TV 211 Interfacing Considerations 212 16. Low-Power Narrowband FM Audio Transmitters 215 17. Serial Data Transmit-Receive System for Remote Control 223 18. RF Field-Strength Meter for 500 kHz to 3 GHz Transmitter 233 Circuit Operation 236 Test Procedure 240 Packaging 241 Parts List 245 19. Low-Power CW Transmitter for 40 Meters 247 20. Single Sideband Basics 253 21. Basic Single Sideband Generator/Exciter Unit 261 22. 1-Watt CW Transmitter for the 1750-Meter “LOWFER” Band 267 23. Simple CW Identifier 273 Circuit Operation 274 Parts List 279 Appendix 281 Part 15 AM Broadcast Applications 281 Part 15 160–190 KHZ (1750 Meters) 282 FM Dipole for 88–108 MHZ 284 Antennas and Induced Hum in Low-Power Transmitters 286 Antenna Considerations and Range Expectations 286 ix This Page Intentionally Left Blank Preface Build Your Own Low-Power Transmitters was written to fill the need for detailed, project-oriented information pertaining to the design and construction of low-power transmitters. Writing this text involved careful incorporation of details and instruc- tion for the successful completion and operation of 20 low-power audio and video transmitter projects. Hobbyists, technicians, amateur radio operators, and general radio enthusiasts of all skill levels will find this book beneficial; however, the content is designed primarily with the needs of intermediate to advanced radio electronics technicians and experimenters in mind. For successful completion of the projects, some experience is assumed on the part of the experimenter. Project areas covered include RF circuitry and digital techniques. PC board construction is largely used with some surface mount construction where necessary. A few of the projects also use microcontrollers. This book contains construction details for audio and video transmitters operat- ing at frequencies from 150 kHz to 1300 MHz for Part 15 operation and for Novice Class Amateur use. Included are several low-power AM and FM audio transmitters, from simple, discrete designs to sophisticated PLL-synthesized types. This book also offers chapters on a frequency-synthesized AM broadcast transmitter for 150-1710 kHz, two FM transmitter designs for 88-108 MHz stereo operation, using PLL syn- thesis digital readouts and microprocessor control, several low-power (0.5-2 watt) TV transmitters covering the 440, 900, and 1300 MHz amateur bands, a data trans- mitter and receiver, and a chapter on video reception techniques for the special fre- quencies used. Other coverage includes a simple low-power CW transmitter, identifier circuits, antennas, and range information. Many projects are of the kind not often seen as published articles. They incorporate modern circuitry techniques, such as PLL syn- thesis and the use of microprocessors. All projects use standard parts and have been thoroughly tested, with PC board layouts given for most of the projects, as well as parts lists, coil data, and complete setup information. Components and suitable enclosures for several projects are available as kits from the source given in the book. These kits include all necessary parts and drilled and etched PC boards. This conve- nience simplifies parts procurement and ensures proper performance of each project. We also discuss the legal limits and ramifications of the equipment and offer sugges- tions and tips for getting the best results from the projects. A lot of effort has gone into making this book an effective, project-oriented tool for hands-on learning about successfully building low-power transmitters. We hope you will enjoy reading the fruit of our labors and working on the projects contained within. Rudolf F. Graf and William Sheets January 2001 xi This Page Intentionally Left Blank 1. Low-Power Transmitters, General The subject of low-power transmitters has always been a fascinating one for experi- menters. They enable you to operate your own radio station, broadcast music, control devices remotely without wires, do surveillance work, eavesdrop on private conver- sations, and other things such as remote sensing. Current Federal Communications Commission (FCC) regulations allow the operation of very low-power unlicensed transmitters subject to various restrictions. These restrictions generally regulate operating range and frequency of operation, as well as possibly types of emission and duration of transmissions. The effort entailed in the construction of these devices will be well rewarded, and the knowledge and experience gained can lead to other pursuits such as ham radio, broadcasting careers, and electronic engineering. Currently, it appears that the low-power FM broadcast transmitter is a popular project. These devices broadcast in the 88–108 MHz band and can have a range of several hundred feet when a sensitive receiver is employed. FCC regulations limit range and field strength at a certain distance. No explicit restrictions are imposed on power, but a single transistor operating at 5 volts or less will easily generate a signal sufficient to accomplish all that is legally allowed for range and field strength. Modern low-power transmitters of this nature are a far cry from the one transistor approach that used to be popular years ago. This approach used an oscillator that is directly modulated with a microphone. FM is obtained by modulating the operating voltages of the oscillator, which in turn affects frequency via a change in transistor parameters. Although this hit-and-miss approach can be made to work, the modern low-power transmitters may employ varactor modulators, microprocessor-controlled frequency synthesis using a phase locked loop (PLL), audio preemphasis, audio mixing and con- trol facilities, and stereo modulator circuitry that generates a “real” baseband multi- plex signal.