Table Of ContentNewnes
Radio Engineer's
Pocket Book
John Davies
(j^ Newnes
Newnes
An imprint of Butterworth-Heinemann
Linacre House. Jordan Hill. Oxford 0X2 8DP
225 Wildwood Avenue. Wobum. MA 01801-204!
A division of Reed Educational and Professional Publishing Ltd
member of the Rccd Elsevier pic group
OXFORD BOSTON JOHANNESBURG
MELBOURNE NEW DELHI SINGAPORE
First published 1994
Reprinted 1998
© John Davies 1994
All rights reserved. No part of this publication
may be reproduced in any material form (including
photocopying or storing in any medium by electronic
means and whether or not transiently or incidentally
to some other use of this publication) without the
written permission of the copyright holder except
in accordance with the provisions of the Copyright,
Designs and Patents Act 1988 or under the terms of a
licence issued by the Copyright Licensing Agency Ltd.
90 Tottenham Court Road, London. England WIP 9HE.
Applications for the copyright holder's written permission
to reproduce any part of this publication should be addressed
to the publishers
British Library Cataloguing in Publication Data
Davies, John
Newnes Radio Engineer's Pocket Booli
I. Title
621.384
ISBN 0 7506 1738 I
Library of Congress Cataloguing in Publication Data
Davies, John
Newnes radio engineer's pocket book/John Davies.
p. cm.
Includes bibliographical references and index.
ISBN 0 7506 1738 1
1. Radio - Handbooks, manuals, etc. 2. Mobile communication
systems - Handbooks, manuals, etc. I. Title. II. Title: Radio engineer's
pocket book.
TK6550.D243 94-12414
62l.384-dc20 CIP
Typeset by TecSet Ltd. Wallington, Surrey
Printed and bound in India at Indira Printers'. New Delhi-110 020
PLANTA
FOB BVHIY Tnve THAT WE MUSH. BunewoeTHHi
WUXrATPOKBTCVTOrLAKTAWCAKEPOKATl
Preface
While this book is intended for reference I have attempted to make it
useful to anyone with a radio interest by including descriptions of
the various processes incurred in radio engineering. If, perhaps,
there is an emphasis on mobile radio, my justification for this is
that it is now probably the fastest growing sector of the industry.
Acknowledgements
I gratefully acknowledge the ready assistance offered by the follow
ing organizations: Andrew Ltd, Aspen Electronics Ltd, BBC, British
Teleconununications pic, FarneQ Instruments Ltd, Independent
Television Authority, International Quartz Devices Ltd, Jaybeam
Ltd, MACOM Greenpar Ltd, Marconi Instruments Ltd,
Panorama Antennas Ltd, Radioconununications Agency, the
Radio Authority, RTT Systems Ltd. A special thanks goes to my
wife Dorothy for once again putting up with my months of seclusion
during the lx)ok*s preparation.
Preface
While this book is intended for reference I have attempted to make it
useful to anyone with a radio interest by including descriptions of
the various processes incurred in radio engineering. If, perhaps,
there is an emphasis on mobile radio, my justification for this is
that it is now probably the fastest growing sector of the industry.
Acknowledgements
I gratefully acknowledge the ready assistance offered by the follow
ing organizations: Andrew Ltd, Aspen Electronics Ltd, BBC, British
Teleconununications pic, FarneQ Instruments Ltd, Independent
Television Authority, International Quartz Devices Ltd, Jaybeam
Ltd, MACOM Greenpar Ltd, Marconi Instruments Ltd,
Panorama Antennas Ltd, Radioconununications Agency, the
Radio Authority, RTT Systems Ltd. A special thanks goes to my
wife Dorothy for once again putting up with my months of seclusion
during the lx)ok*s preparation.
1 Propagation of radio waves
1.1 Frequency and wavelength
Thereisa fixed relationship betweenthefrequency and thewave
length, whichisthedistancebetweenidenticalpointsontwoadja
cent waves (Figure \.I), ofany type of wave: sound (pressure),
electromagnetic(radio)andlight. The typeofwaveand the speed
atwhichthewavefronttravelsthroughthemediumdeterminesthe
relationship. Thespeedofpropagation isslower inhigherdensity
media.
Wavelength ().)
I· (metres) ·1
Time
(seconds)-
figure1.1 Frequencyandwavelength
Soundwavestravelmoreslowlythanradioandlightwaveswhich,
infreespace,travelatthesamespeed,approximately3x loametres
persecond, and the relationshipbetweenthefrequency and wave
lengthofaradiowaveisgivenby:
3x loa
1=-f--metres
whereIisthewavelengthandf isthefrequencyinhertz(Hz).
1.2 The radio frequency spectrum
TheelectromagneticwavespectrumisshowninFigure 1.2:thepart
usablefor radiocommunicationrangesfrom below 10kHztoover
IOOGHz.
Theradiospectrumisdividedintobandsandthedesignationof
thebands,theirprincipaluscandmethodofpropagationisshownin
Table1.1.Wavesofdifferentfrequenciesbehavedifferentlyandthis,
along with the amount of spectrum available in terms of radio
communicationchannelsineachband,governstheirusc.
2
Visiblespectrum
•II Cotn'!ie"'f$
tnt,.-.ed Uh...·
'.-,so. ""~I
.";..-thell
~io t.eouef1Ctt15 G'If'"I'''"Wl
~freql,lenc;"
H.t kHJ hlHI 'er 'rr MHI
10 100 1 ',0.100 ~ 11~ 10''':10' ltr10'10" ,~" 10"10"10"10"10'"10'" Frequ.ncy
10' 10"1cr10"100010010 1 10 1\0'10110'10"0"0"10"0"0'10"'0"10'IW.ve!engtn
m m
Rgure1.2 Theelectromagneticwavespectrum
u..
Tmie1.1 ofredlofrequencies
FrequtlllCyband Designation,USBandpropagatk1n
~kHz Verylowfrequency(VlF).Worldwideandlong
distancecorrvnunication.Surfacewave.
30-300kHz lowfrequency(IF).longdistance
communication,long-wavebroadcasting.
Groundwave.
300-3000kHZ Mediumfrequency(MF).Medium-wave
broadcasting.Groundwave.
3-30MHz Highfrequency(HF).longdistance
communication,short-wBvebroadcasting.Sky
WBve.
30-300MHz Veryhighfrequency(VHF).Shortrangeand
mobilecommunication,soundbroadcasting.
Spacewave.
300-3000MHz Ultrahighfrequency(UHF).Shortrangeand
mobilecommunication,televisionbroadcasting,
point-to-pointlinks.Spacewave.
3-30GHZ Superhighfrequency(SHF).Point-to-point
links,radar,satatlhecommunication.Space
wave.
Above30GHz Extrahighfrequency(EHF).Inter-satatlheand
micro-<:ellularradio-telephone.Spacewave.
1.3 The isotropic radiator
Astartingpointforconsideringthepropagationofradio-orIight
wavesistheisotropicradiator,animaginarypointsourceradiating
equallyinalldirectionsinfreespace.Sucharadiatorplacedatthe
centreofa sphereilluminatesequally the completesurfaceofthe
sphere.Asthesurfaceareaofasphereisgivenby4".,2where,isthe
radiusofthesphere,thebrillanceofilluminationatanypointonthe
surfacevariesinverselywiththedistancefromtheradiator.Inradio
tenns,thepowerdensityatdistancefromthesourceisgivenby:
=..!l
Pd
4".,.2
whereP,= transmittedpower.
3
1.4 Formation ofradio "aves
Radio waves are elcctromagnetic. They contain both electric and
magneticfieldsatrightanglestoeachotherandalsoatrightangles
tothedirectionofpropagation.Analternatingcurrentflowingina
conductorproducesanalternatingmagneticfieldsurroundingitand
analternatingvoltagegradient- anelectricfield- alongthelength
oftheconductor.Thefieldscombinetoradiatefromtheconductor
asinFigure1.3.
Eplane
Hplane
Hfield
FIgure1.3 Formationofelectromagneticwave
TheplaneoftheelectricfieldisreferredtoastheEplaneandthat
ofthemagneticfieldastheHplane.Thetwofieldsareequivalentto
the voltage and current in a wired circuit. They are measured in
similarterms,voltspermetreandamperespermetre,andthemed
iumthroughwhich theypropagatepossessesanimpedance.Where
E= ZIinawiredcircuit,foranelectromagneticwave:
E=ZH
where
E= theRMSvalueoftheelectricfieldstrength,V/metre
H= theRMSvalueofthemagneticfieldstrength,A/metre
Z=characteristicimpedanceofthemedium,ohms
The voltage is that which the wave, passingat the speed oflight,
wouldinduceinaconductoronemetrelong.
Thecharacteristicimpedanceofthemediumdependsonitsper
meability(equivalentofinductance)andpermittivity(equivalentof
capacitance).Takingtheacceptedfiguresforfreespaceas:
I'=411'X 10-7henrys(H)permetre(permeability)and
<= 1/361rX 109farads(F)permetre(permittivity)
thentheimpedanceoffreespace,Z,isgivenby:
{§
= 1201l'= 3770hms
Therelationshipbetweenpower,voltageandimpedanceisalsothe
sameforelectromagneticwavesasforelectricalcircuits,W= E2/Z.
Thesimplestpracticalradiatoristheelementarydoubletformedby
openingouttheendsofapairofwires. Fortheoreticalconsidera
tionsthelengthoftheradiatingportionsofthewiresismadevery
shortinrelationtothewavelengthoftheappliedcurrenttoensure
4
unifonncurrentdistributionthroughouttheirlength. Forpractical
applicationsthelengthoftheradiatingelementsisonehalf-wave
length(>./2)andthedoubletthenbecomesadipoleantenna(Figure
1.4).
A
2
---- Voltagedistribution
--- Currentdistribution
Figure1.4 Doublet(dipole)antenna
Whenradiationoccursfromadoubletthewaveispolarized.The
electricfield liesalongthelengthoftheradiator(theEplane)and
themagueticfield(theHplane)atrightanglestoit.IftheEplaneis
vertical,theradiatedfieldissaidtoverticallypolarized.Referenceto
theEandHplanesavoidsconfusionwhendiscussingthepolariza
tionofanantenna.
Unlike the isotropic radiator, the dipole possesses directivity,
concentrating the energy in the H plane at the expense ofthe E
plane. Iteffectively provides a power gain in the direction ofthe
Hplanecomparedwithanisotropicradiator.Thisgainis1.6times
or2.15dBi(dBimeansdBrelativetoanisotropicradiator).
Foradirectraythepowertransferbetweentransmittingandreceiv
ing isotropic radiators is inversely proportional to the distance
betweentheminwavelengths.Thefreespacepowerlossisgivenby:
(4'11'd)2
Freespaceloss,dB= 1010gl0---:\2
wheredand>.areinmetres,or:
Freespaceloss(dB)= 32.4+20xloglod+20x10glO!
whered= distanceinkmand!= frequencyinMHz.
Thefreespacepowerloss,therefore,increasesasthesquareofthe
distanceandthefrequency. ExamplesareshowninFigure 1.5.
Withpracticalantennas,thepowergainsofthetransmittingand
receivingantennas, indBi,must besubtractedfrom thefreespace
losscalculatedasabove.Alternatively,thelossmaybecalculatedby:
180
170 7000MHz
3500MHz
160 2000MHz
1000MHz
150
iii
~ 400MHz
::: 140
.2 200MHz
100MHz
110
100
90 1...-...-l__L-.....I.......1.---.L_.....I....-'-_.L..-.L..-...J
10 20 30 50 70 100 200300 500700 1000
Distance(km)
Figure1.5 Freespacelossvs.distanceandfrequency
<411"d)2 I]
Freespaceloss(dB)= 1010gl0[~ XG, xG
r
whereG, andG arethe respectiveactualgains, notindB,ofthe
r
transmittingandreceivingantennas.
1.5 Behaviour ofradio waves
1.5.1 P1IYl1ka1effects
Thephysicalpropertiesofthe medium throughwhich awave tra
vels, and objectsinorclose toits path,affect thewavein various
ways.
A.bsorption
Intheatmosphereabsorptionoccursandenergyislostinheatingthe
airmolecules. Absorptioncaused bythisisminimalat frequencies
belowabout 10GHz butabsorption by foliage, particularly when
wet,issevereatVHFandabove.
Waves travellingalongtheearth'ssurfacecreatecurrentsin the
earthcausinggroundabsorptionwhichincreaseswithfrequency.A
horizontallypolarizedsurfacewavesuffersmoregroundabsorption
thanaverticaUypolarizedwavebecauseofthe'short-circuiting'by
thegroundoftheelectricfield. Attenuationatagivenfrequencyis
leastforpropagationoverwaterandgreatestoverdrygroundfora
verticallypolarizedwave.
6
Refractionanditseffectontheradiohorizon
Asradiowavestravelmoreslowlyindensemediaandthedensest
partoftheatmosphereisnormallythelowest,theupperpartsofa
waveusuallytravelfasterthanthelower.Thisrefraction(Figure1.6)
has theeffectofbending the wave to follow the curvature ofthe
earth and progressively tilting the wavefront until eventually the
wave becomes horizontally polarized and short·circuited by the
earth'sconductivity.
Progressivelytilting
wavefront
Pathof
refractedwave
Figure1.6 Effectsofrefraction
Waves travelling above the earth's surface (space waves) are
usually refracted downwards,effectivelyincreasing the radio hori·
zontogreaterthanthevisual.
The refractive index ofthe atmosphere is referred to as the K
factor; aK factor of Iindicateszero refraction. Mostofthe time
K is positive at 1.33 and the wave is bent to follow the earth's
curvature. The radio horizon is then 4/3 times the visual.
However, the density ofthe atmosphere varies from time to time
andindifferentpartsoftheworld.Densityinversionswherehigher
densityairisabovearegionoflowdensitymayalsooccur. Under
theseconditions the K factorisnegativeandradiowaves arebent
awayfromtheearth'ssurfaceandareeitherlostorductingoccurs.
AKfactorof0.7istheworstexpectedcase.
Ductingoccurswhenawavebecomestrappedbetweenlayersof
differing density only to be returned at a great distance from its
source,possiblycreatinginterference.
Agoodapproximationoftheradiohorizonisgivenby:
d,= 4,fh.
where
d,=distancefrom transmittingantenna,km
h,= heightoftransmittingantennaaboveground,m
Repeating thecalculation for the receivingstationand adding the
resultsgivesthetotalpathlength.
Diffraction
When a wave passes overon the edgeofan obstacle some ofits
energyisbentinthedirectionoftheobstacletoprovideasignalin
whatwouldotherwisebeashadow.Thebendingismostseverewhen
thewavepassesoverasharpedge(Figure 1.7).
Aswithlightwaves,thesubsequentwavefrontconsistsofwavelets
producedfromaninfinitenumberofpointsonthewavefront,raysa
andbinFigure1.7(Huygens'principle).Thisproducesapatternof
interferingwavesofalternateadditionandsubtraction.
