Radio Communication Handbook

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Published by the Radio Society of Great Britain 3 Abbey Court Fraser Road Priory Business Park Bedford. MK44 3WH Tel 01234 832700 Web www rsgb org,First published 2011. Radio Society of Great Britain 2011 All rights reserved No part of this publication may be reproduced. stored in a retrieval system or transmitted in any form or by any means electronic mechanical photo. copying recording or otherwise without the prior written permission or the Radio Society of Great Britain. Cover design Kim Meyern,Production Mark Allgar M1MPA. Design and layout Mike Dennison G3XDV Emdee Publishing. Printed in Great Britain by Latimer Trend of Plymouth. Companion CD printed by DBMasters of Faversham England www dbmasters co uk. The opinions expressed in this book are those of the author s and are not necessarily those of the Radio. Society of Great Britain Whilst the information presented is believed to be correct the publishers and their. agents cannot accept responsibility for consequences arising from any inaccuracies or omissions. ISBN 9781 9050 8674,Acknowledgements iii,Preface vii. Chapter 1 Principles 1 1,Chapter 2 Passive components 2 1. Chapter 3 Semiconductors and valves 3 1,Chapter 4 Building blocks 1 Oscillators 4 1.
Chapter 5 Building blocks 2 Amplifiers mixers etc 5 1. Chapter 6 HF receivers 6 1,Chapter 7 HF transmitters and transceivers 7 1. Software defined radio 8 1, VHF UHF receivers transmitters and transceivers 9 1. Chapter 10 Low frequencies Below 1MHz 10 1, Chapter 11 Practical microwave receivers and transmitters 11 1. Chapter 12 Propagation 12 1,Chapter 13 Antenna basics and construction 13 1. Chapter 14 Transmission lines 14 1,Chapter 15 Practical HF antennas 15 1.
Chapter 16 Practical VHF UHF antennas 16 1,Chapter 17 Practical microwave antennas 17 1. Chapter 18 The great outdoors 18 1,Chapter 19 Morse code 19 1. Chapter 20 Digital communications 20 1,Chapter 21 Computers in the shack 21 1. Chapter 22 Electromagnetic compatibility 22 1,Chapter 23 Power supplies 23 1. Chapter 24 Measurement and test equipment 24 1, Chapter 25 Construction and workshop practice 25 1.
Appendix A General data A 1,Appendix B Printed circuit board artwork B 1. Note Many chapters have references to the RSGB Bulletin Radio Communication or RadCom These are historic names of the. RSGB members monthly journal The magazines are available on a series of CD ROMs from RSGB 3 Abbey Court Fraser Road. Priory Business Park Bedford MK44 3WH www rsgb org. 6 Receivers Roger Wilkins G8NHG, CW SSB only and depending for performance rather more on. the skill of the operator can be relatively simple to build at low. As with other branches of electronics the practical imple. mentation of high performance communications receivers has. undergone a number of radical changes since their initial devel. opment in the mid 1930s some resulting from the improved. stability needed for SSB reception and others aimed at reducing. costs by substituting electronic techniques in place of mechani. cal precision, However it needs to be emphasised that in most cases. progress in one direction has tended to result in the introduction. Fig 6 1 The AOR 7030 is a sophisticated receiver covering the of new problems or the enhancement of others What we call. frequency range 0 32MHz progress is the exchange of one nuisance for another nuisance. Havelock Ellis or Change is certain progress is not A J P. Amateur HF operation whether for two way contacts or for lis Taylor As late as 1981 an Australian amateur was moved to. tening to amateur transmissions imposes stringent require. SG write Solid state technology affords commercial manufacturers. ments on the receiver The need is for a receiver that enables an cheap large scale production but for amateur radio receivers. experienced operator to find and hold extremely weak signals on and transceivers of practical simplicity valves remain incompa. frequency bands often crowded with much stronger signals from rably superior for one off home built projects. local stations or from the high power broadcast stations using The availability of linear integrated circuits capable of form. adjacent bands The wanted signals may be fading repeatedly to ing the heart of communications receivers combined with the. below the external noise level which limits the maximum usable increasing scarcity and hence cost of special valve types has. sensitivity of HF receivers and which will be much higher than tended to reverse this statement It is still possible to build rea. in the VHF and UHF spectrum sonably effective HF receivers particularly those for limited. Although the receivers now used by most amateurs form part frequency coverage on the kitchen table with the minimum of. of complex factory built HF transceivers the operator should test equipment. understand the design parameters that determine how well or. how badly they will perform in practice and appreciate which. design features contribute to basic performance as HF commu. nications receivers as opposed to those which may make them. more user friendly but which do not directly affect the reception. of weak signals This also applies to dedicated receivers that are. factory built such as the one shown in Fig 6 1, Ideally an HF receiver should be able to provide good intelli. gibility from signals which may easily differ in voltage delivered. from the antenna by up to 10 000 times and occasionally by up. to one million times 120dB from less than 1 V from a weak. signal to nearly 1V from a near neighbour Table 1 shows the. relationship between the various ways of measuring the input. signals pd potential difference and dBm input power are. most commonly used, To tune and listen to SSB or to a stable CW transmission while.
using a narrow band filter the receiver needs to have a fre. quency stability of within a few hertz over periods of 15 minutes. or so representing a stability of better than one part in a million. It should be capable of being tuned with great precision either. continuously or in increments of at most a few hertz. A top quality receiver may be required to receive transmis. sions on all frequencies from 1 8MHz to 30MHz or even. 50MHz to provide general coverage or only on the bands allot. ted to amateurs Such a receiver may be suitable for a number. of different modes of transmission SSB CW AM NBFM data. RTTY packet etc with each mode imposing different require. ments in selectivity stability and demodulation decoding. Such a receiver would inevitably be complex and costly to buy. On the other hand a more specialised receiver covering only. a limited number of bands and modes such as CW only or Table 6 1 The relationship between emf pd and dBm. The Radio Communication Handbook 6 1,6 HF RECEIVERS. Furthermore since many newcomers will eventually acquire In recent years significant progress has continued to be. a factory built transceiver but require a low cost stand alone made in meeting these requirements although we are still. HF receiver in the interim period the need can be met either by some way short of being able to provide them over the entire. building a relatively simple receiver or by acquiring and if nec signal range of 120dB at the ideal few hertz stability The. essary modifying one of the older valve type receivers that introduction of more and more semiconductor devices into. were built in very large numbers for military communications receivers has brought a number of very useful advantages but. during the second world war or those marketed for amateur has also paradoxically made it more difficult to achieve the. operation in the years before the virtually universal adoption of highly desirable wide dynamic range Professional users now. the transceiver require frequency read out and long term stability of an. Even where an amateur has no intention of building or servic extremely high order better than 1Hz stability is needed for. ing his or her own receiver it is important that he or she should some applications and this has led to the use of frequency. have a good understanding of the basic principles and limita synthesised local oscillators and digital read out systems. tions that govern the performance of all HF communications although these are effective for the purposes which led to their. receivers adoption they are not necessarily the correct approach for. amateur receivers since unless very great care is taken a. BASIC REQUIREMENTS complex frequency synthesiser not only adds significantly to. The main requirements for a good HF receiver are the cost but may actually result in a degradation of other even. more desirable characteristics, Sufficiently high sensitivity coupled with a wide dynamic So long as continuous tuning systems with calibrated dials. range and good linearity to allow it to cope with both the were used the mechanical aspects of a receiver remained very. very weak and very strong signals that will appear togeth important it is perhaps no accident that one of the outstanding. er at the input it should be able to do this with the mini early receivers HRO was largely designed by someone whose. mum impairment of the signal to noise ratio by receiver. SG early training was that of a mechanical engineer. noise cross modulation blocking intermodulation recip It should be recognised that receivers which fall far short of. rocal mixing hum etc ideal performance by modern standards may nevertheless still. Good selectivity to allow the selection of the required sig provide entirely usable results and can often be modified to. nal from among other possibly much stronger signals on take advantage of recent techniques Despite all the progress. adjacent or near adjacent frequencies The selectivity made in recent decades receiver designs dating from the thir. characteristics should match the mode of transmission ties and early forties are still capable of being put to good use. so that interference susceptibility and noise bandwidth provided that the original electrical and mechanical design was. should be as close as possible to the intelligence band sound Similarly the constructor may find that a simple straight. width of the signal forward and low cost receiver can give good results even when. Maximum freedom from spurious responses that is to its specification is well below that now possible It is ironical that. say signals which appear to the user to be transmitting on almost all the design trends of the past 30 years have until. specific frequencies when in fact this is not the case Such quite recently impaired rather than improved the performance. spurious responses include those arising from image of receivers in the presence of strong signals. responses breakthrough of signals and harmonics of the. receiver s internal oscillators BASIC TYPES OF RECEIVERS. A high order of stability in particular the absence of short Amateur HF receivers fall into one of two main categories. term frequency drift or jumping, Good read out and calibration of the frequency to which a straight regenerative and direct conversion receivers in. the set is tuned coupled with the ability to reset the which the incoming signal is converted directly into audio by. receiver accurately and quickly to a given frequency or sta means of a demodulator working at the signal frequency. tion b single and multiple conversion superhet receivers in which. Means of receiving SSB and CW normally requiring a sta the incoming signal is first converted to one or more inter. ble beat frequency oscillator preferably in conjunction with mediate frequencies before being demodulated Each type. product detection of receiver has basic advantages and disadvantages. Sufficient amplification to allow the reception of signals of. under 1 V input this implies a minimum voltage gain of. Regenerative Detector Straight or TRF, about one million times 120dB preferably with effective Receivers. automatic gain control AGC to hold the audio output At one time valve receivers based on a regenerative reaction. steady over a very wide range of input signals detector plus one or more stages of AF amplification ie 0 V 1. Sturdy construction with good quality components and 0 V 2 etc and sometimes one or more stages of RF amplifica. with consideration given to problems of access for servic tion at signal frequency 1 V 1 etc were widely used by ama. ing when the inevitable occasional fault occurs teurs High gain can be achieved in a correctly adjusted regen. erative detector when set to a degree of positive feedback just. A number of other refinements are also desirable for example beyond that at which oscillation begins this makes a regenera. it is normal practice to provide a headphone socket on all com tive receiver capable of receiving weak CW and SSB signals. munications receivers it is useful to have ready provision for However this form of detector is non linear and cannot cope well. receiver muting by an externally applied voltage to allow voice in situations where the weak signal is at all close to a strong sig. operated push to talk or CW break in operation an S meter to nal it is also inefficient as an AM detector since the gain is much. provide immediate indication of relative signal strengths a reduced when the positive feedback regeneration is reduced. power take off socket to facilitate the use of accessories an IF below the oscillation threshold Since the detector is non linear. 6 2 The Radio Communication Handbook Furthermore since many newcomers will eventually acquire a factory built transceiver but require a low cost stand alone HF receiver in the interim period the need can be met either by building a relatively simple receiver or by acquiring and if nec essary modifying one of the older valve type receivers

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