Practical communication theory

176 Pages·2014·8.67 MB·English

by  David Adamy

Practical
Communication
Theory

Practical
Communication
Theory
2nd Edition
Dave Adamy
Edison, NJ scitechpub.com
PublishedbySciTechPublishing,animprintoftheIET.
www.scitechpub.com
www.theiet.org
Copyright†1994byLYNXPublishing
Copyright†2014bySciTechPublishing,Edison,NJ.Allrightsreserved.
Firstedition1994
Secondedition2014
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Whiletheauthorandpublisherbelievethattheinformationandguidancegiveninthisworkare
correct,allpartiesmustrelyupontheirownskillandjudgementwhenmakinguseofthem.
Neithertheauthornorpublisherassumesanyliabilitytoanyoneforanylossordamagecaused
by any error or omission in the work, whether such an error or omission is the result of
negligenceoranyothercause.Anyandallsuchliabilityisdisclaimed.
Editor:DudleyR.Kay
10987654321
ISBN978-1-61353-186-0(hardback)
ISBN978-1-61353-187-7(PDF)
TypesetinIndiabyMPSLimited
PrintedintheUSbyIntegratedBooksInternational
PrintedintheUKbyCPIGroup(UK)Ltd,Croydon
Contents
AbouttheAuthor ix
Preface xi
Preface totheFirstEdition xii
Acknowledgements xiv
1 Introduction 1
1.1 The Communication Link 1
1.2 AFewImportant Definitions 3
1.3 Assumptions 4
1.4 Scope of the Book 4
Appendixes 4
2 AboutdB 7
2.1 Conversion todB Form 8
2.2 Absolute Values in dB Form 9
2.3 dB Formsof Equations 9
2.4 Quick Conversions to dBValues 10
2.5 dB Bookkeeping Diagrams 12
3 Signal-to-Noise Ratio 15
3.1 Noise 15
3.2 Signal-to-Noise Ratio 16
3.3 Other Related Ratios 18
3.3.1 RFSNR 18
3.3.2 Signal-to-Quantization Ratio 18
3.4 Background Noise 19
4 The CommunicationLink 23
4.1 Information Signals 23
4.1.1 Audio Signals 23
4.1.2 Digital Data 24
4.1.3 Video Signals 25
4.2 Transmitters 27
4.2.1 Modulator 28
4.2.2 PowerAmplifier 35
vi Practical CommunicationTheory
4.3 Receivers 36
4.3.1 Fixed Tuned Receiver 37
4.3.2 Channelized Receiver 37
4.3.3 Superheterodyne Receiver 38
4.3.4 Crystal Video Receiver 40
4.3.5 IFMReceiver 41
4.3.6 Compressive Receiver 41
4.3.7 Digital Receiver 42
4.3.8 Receiving Systems 43
4.4 Antennas 44
4.4.1 Antenna Gain Pattern 44
4.4.2 Polarization 47
4.4.3 Types of Antennas 49
4.5 Antenna Slide Rule 55
4.5.1 Antenna Scales 56
4.5.2 Finding Gain and Beamwidth 56
4.6 The Ether Waves 60
5 The LinkEquation 61
5.1 Link Losses 63
5.1.1 Free Space 63
5.1.2 Two-Ray Loss 67
5.1.3 Fresnel Zone 70
5.1.4 Knife-Edge Diffraction 73
5.1.5 Atmospheric Loss 75
5.2 Signal Strength at VariousPointsin the Communication Link 76
5.2.1 Effective Radiated Power 77
5.2.2 Signal Arriving at Antenna 79
5.2.3 Received Power 80
5.3 Link Design Parameters 81
5.3.1 Required Margin 81
5.3.2 Required Sensitivity 82
5.3.3 Effective Range 83
5.3.4 Required Transmitter Poweror Antenna Gain 86
5.4 Interfering Signals 88
5.5 Dynamic Range 91
6 Receiver Sensitivity andDynamic Range 93
6.1 Sensitivity 93
6.1.1 Thermal Noise Level 94
6.1.2 Noise Figure 95
6.1.3 Required SNR 98
6.2 Digitized Analog Signals 99
6.2.1 Sampling Rate 100
6.2.2 Quantizing Levels 100
6.2.3 RFSNR 101
Contents vii
6.3 Dynamic Range 102
6.3.1 Analog versusDigital Dynamic Range 103
6.3.2 Analog Receiver Dynamic Range 104
6.3.3 Determining Dynamic Range 106
6.4 Digital Dynamic Range 107
7 Challenging Conditions 109
7.1 Rain and FogAttenuation 109
7.2 Non–Line of Sight Transmission 111
7.2.1 Knife Edge Diffraction 111
7.2.2 Diffraction Lossover a Smooth Sphere 112
7.3 Doppler Effect 113
7.4 Antenna Misalignment 114
AppendixA Derivation of EquationsandCharts 117
AppendixB Signal Strengthin the Ether Waves 123
AppendixC Quick Formulas for Antennas 127
AppendixD Quick Formulas for Receiver Sensitivity and
Dynamic Range 133
AppendixE Quick Formulas for Propagation 137
AppendixF Quick FormulasFor Doppler Shift 149
AppendixG AntennaandPropagationSlide Rule 151
Index 157

About the Author
You know perfectly well that authors write these ‘‘about the author’’ sections
themselves, but write inthe third personto somehow imply that an impartial third
partyisheapingonallthatpraise.Asyouwillseewhilereadingthisbookandthen
using it in your work, I have a great deal more respect for your intelligence and
yourvaluable time than that.
The most important thing you should know about me is that I have actually
usedalloftheworkingtoolspresentedinthisbook,outinthe ‘‘hardcruel world’’
where making a large mistake usually costs your boss or your customer a lot of
troubleand/ormoney.Inafewcases,ithasliterallybeenamatteroflifeanddeath.
Ihavealsospentyearsasatechnicalmanagerofyoung,eagerengineerswhowere
(andare)alotsmarterthanI,butsomeofwhomoccasionallytriedtodefythelaws
of physics in paper designs that were not always corrected before we built some-
thingthatdidn’tdowhatourcustomershadarighttoexpect(andwhichIenjoyed
helping repair during many long nights).
With over 50 years in the business, I have participated in the design, manu-
facture,testingandfieldsupportofawiderangeofsystemsandsubsystemswhich
eithertransmitorreceiveradiosignalsinenvironments,fromsubmarinestospace,
and over frequency ranges from just above DCto just above light.
IholdaBSEEfromArizonaStateUniversityandanMSEEfromtheUniversity
of Santa Clara, both with majors in communication theory. I have published
15technicalbooksandmorethan200articlesoncommunicationsrelatedtopicsina
variety of technical magazines and journals, including extensive tutorial sections
in various handbooks. I have never published an integral sign (except once in a
cartoon), all of these books, articles and tutorial sections have explained commu-
nications phenomena using the same practical, application oriented approach used
throughoutthisbook.
For the last 30 years, I have made my living as owner of a small company
that performs communications related design studies for large companies and the
government.Ialsoteachshortcoursesallovertheworldonavarietyofsubjectsfor
which a practical understanding of radio propagation is essential. In fact, the real
reason for this book is that so many people in those classes found the techniques
presented uniquely useful to them.
Ifyouhaveatechnicalquestion,needareferraltoanexpertinarelatedfield,or
justwanttobragaboutaclevercalculationtechniquetoanappreciativecolleague,