Radio and Electronics Cookbook

Radio and ElectronicsCookbook

Edited byDr George Brown, CEng, FIEE, M5ACN

OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI

NewnesAn imprint of Butterworth-HeinemannLinacre House, Jordan Hill, Oxford OX2 8DP225 Wildwood Avenue, Woburn, MA 01801-2041A division of Reed Educational and Professional Publishing Ltd

A member of the Reed Elsevier plc group

First published 2001

Radio Society of Great Britain 2001

All rights reserved. No part of this publication may be reproduced inany material form (including photocopying or storing in any medium byelectronic means and whether or not transiently or incidentally to someother use of this publication) without the written permission of thecopyright holder except in accordance with the provisions of the Copyright,Designs and Patents Act 1988 or under the terms of a licence issued by theCopyright Licensing Agency Ltd, 90 Tottenham Court Road, London,England W1P 0LP. Applications for the copyright holders writtenpermission to reproduce any part of this publication should be addressedto the publishers

British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library

ISBN 0 7506 5214 4

RSGBLambda HouseCranborne RoadPotters BarHertsEN6 3JE

Composition by Genesis Typesetting, Laser Quay, Rochester, KentPrinted and bound in Great Britain

v

Contents

Preface ix

1. A medium-wave receiver 1

2. An audio-frequency amplifier 4

3. A medium-wave receiver using a ferrite-rod aerial 9

4. A simple electronic organ 12

5. Experiments with the NE555 timer 17

6. A simple metronome 21

7. What is a resistor? 24

8. Waves Part 1 27

9. A beat-frequency oscillator 31

10. What is a capacitor? 34

11. Waves Part 2 38

12. An LED flasher 41

13. Waves Part 3 44

14. Choosing a switch 46

15. An aerial tuning unit for a receiver 49

16. A simple 2 m receiver preamplifier 52

17. Receiving aerials for amateur radio 54

18. The Colt 80 m receiver Part 1 58

19. A crystal radio receiver 62

20. The varactor (or varicap) diode 64

21. A portable radio for medium waves 65

22. The Colt 80 m receiver Part 2 70

Contents

vi

23. A simple transistor tester 73

24. An introduction to transmitters 77

25. The Colt 80 m receiver Part 3 81

26. A two-way Morse practice system 88

27. The Colt 80 m receiver Part 4 91

28. A simple crystal set 95

29. A crystal calibrator 100

30. A simple short-wave receiver Part 1 104

31. A fruit-powered medium-wave radio 106

32. A capacitance bridge 109

33. A simple short-wave receiver Part 2 113

34. A basic continuity tester 117

35. A charger for NiCad batteries 119

36. An 80 metre crystal-controlled CW transmitter 123

37. A solar-powered MW radio 129

38. A receiver for the 7 MHz amateur band 133

39. Diodes for protection 137

40. An RF signal probe 140

41. An RF changeover circuit 142

42. A low-light indicator 146

43. A J-pole aerial for 50 MHz 149

44. Measuring light intensity the photometer 153

45. A 70 cm Quad loop aerial 156

46. A UHF field strength meter 160

47. Christmas tree LEDs 162

48. An audio signal injector 166

49. Standing waves 168

50. A standing-wave indicator for HF 170

51. A moisture meter 174

52. Simple aerials 177

53. A breadboard 80 cm CW transmitter 182

Contents

vii

54. A 7-element low-pass filter for transmitters 186

55. Radio-frequency mixing explained 189

56. A voltage monitor for a 12 V power supply 192

57. A 1750 Hz toneburst for repeater access 196

58. A circuit for flashing LEDs 201

59. Digital logic circuits 205

60. A resistive SWR indicator 210

61. An audio filter for CW 213

62. An electronic die 215

63. The absorption wavemeter 222

64. An HF absorption wavemeter 224

65. A vertical aerial for 70 cm 228

66. A UHF corner reflector aerial 230

67. A switched dummy load 234

68. A simple Morse oscillator 238

69. A bipolar transistor tester 240

70. The Yearling 20 m receiver 245

71. Adding the 80 metre band to the Yearling receiver 251

72. How the Yearling works 255

73. A field strength meter 258

74. Preselector for a short-wave receiver 261

75. An audible continuity tester 265

76. An experimental 70 cm rhombic aerial 268

77. Water level alarm 272

78. A delta loop for 20 metres 275

79. A simple desk microphone 279

80. Morse oscillator 284

81. A simple 6 m beam 287

82. An integrated circuit amplifier 291

83. A novice ATU 293

84. CW QRP transmitter for 80 metres 297

Contents

viii

85. An audio booster for your hand-held 303

86. A grid dip oscillator 306

87. A CW transmitter for 160 to 20 metres 312

88. Matching the end-fed random-wire aerial 315

Preface

Although we are surrounded by sophisticated computerised gadgets thesedays, there is still a fascination in putting together a few resistors, capacitorsand the odd transistor to make a simple electronic circuit. It is reallysurprising how a handful of components can perform a useful function, andthe satisfaction of having built it yourself is incalcuable.

This book aims to provide a wide variety of radio and electronic projects,from something that will take a few minutes to a more ambitious weekendsworth. Various construction techniques are described, the simplest requiringno more than a small screwdriver, the most complex involving printedcircuit boards.

Originally published by the Radio Society of Great Britain, the projects wereall chosen to be useful and straightforward, with the emphasis onpracticality. In most cases the workings of the circuit are described, and theprojects are backed up by small tutorials on the components and conceptsemployed. In the 21st century it may seem strange that few of the publishedcircuits use integrated circuits (chips). This is intentional as it is much easierto understand how the circuit works when using discrete components.

Anyone buying the Radio and Electronics Cookbook will find that it willlead to hours of enjoyment, some very useful and entertaining gadgets, andincreased knowledge of how and why electronics circuits work, and a greatsense of satisfaction. Beware, electronic construction is addictive!

WARNING: This book contains construction details of transmitters.It is illegal to operate a transmitter without the appropriate licence.Information on how to obtain an Amateur Radio Licence can beobtained from the Radiocommunications Agency, tel. 020 72110160.

A medium-wave receiver

1

1 A medium-wave receiver

IntroductionLet us start off with something that is really quite simple and yet is capableof producing a sense of real satisfaction when complete a real medium-wave (MW) radio receiver! It proves that receivers can be simple and, at thesame time, be useful and enjoyable to make. To minimise the confusion toabsolute beginners, no circuit diagram is given, only the constructionaldetails. The circuits will come later, when you have become accustomed tothe building process. In the true amateur spirit of ingenuity andinventiveness, the circuit is built on a terminal strip, the coil is wound ona toilet roll tube (as amateur MW coils have been for 100 years!), and thereceiver is mounted on a piece of wood.

Putting it togetherStart by mounting the components on the terminal strip as shown in Figure1, carefully checking the position and value of each one. The threecapacitors are all the same, and so present no problem. They (and theresistors) may be connected either way round, unlike the two semi-conductors (see later). The resistors are coded by means of coloured bands.You can refer to Chapter 7 if you have difficulty remembering the coloursand their values.

Figure 1 Terminal strip position of components

Radio and Electronics Cookbook

2

1. Brown, Black, Yellow 100 000 ohms (R1, R5, R6)2. Green, Blue, Brown 560 ohms (R2)3. Red, Violet, Brown 270 ohms (R3)4. Brown, Black, Orange 10 000 ohms (R4)

The integrated circuit (the ZN414Z) and the transistor (the BC184) must beconnected correctly. Check Figure 1 carefully before fitting each device.

Now wind the coil. Most tubes are about 42 mm diameter and 110 mmlong. Dont worry if your tube is slightly different; it shouldnt matter. Maketwo holes, about 3 mm apart, about 40 mm from one end, as shown inFigure 2. Loop your enamelled wire into one hole and out of the other, anddraw about 100 mm through; loop this 100 mm through again, thusanchoring the wire firmly. Now wind on 80 turns, keeping the wire tightand the turns close together but not overlapping. After your 80th turn,make another two holes and anchor the wire in the same way as before.Again, leave about 100 mm free after anchoring. Using another piece ofenamelled wire (with 100 mm ends as before), loop one end through thesame two holes which contain the end anchor of the last winding, wind twoturns and anchor the end of this short winding using another pair of holes.Figure 2 shows the layout.

Figure 2 The layout of theparts on the wooden base

A medium-wave receiver

3

With some glass paper, remove the enamel from the ends of both piecesof wire which go through the same holes (i.e. the bottom of the large coiland the top of the small coil), then twist these bare ends together.Remove the enamel from the remaining ends of the coil. The co