HF communications sóng ngắn

HF Communications: A Systems Approach Nicholas M Maslin MA, PhD, CEng, MIERE Principal Consultant, Software Sciences Ltd Pitman PITMAN PUBLISHING 128 Long Acre, London WC2E 9AN © N M Maslin 1987 First published in Great Britain 1987 This edition published in the Taylor & Francis e-Library, 2005 “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” British Library Cataloguing in Publication Data Maslin, N.M HF communications: a systems approach Telecommunication systems I Title 621.38 TK5101 ISBN 0-273-02675-5 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, photocopying, recording and/or otherwise without the prior written permission of the publishers This book may not be lent, resold, hired out or otherwise disposed of by way of trade in any form of binding, or cover other than that in which it is published, without the prior consent of the publishers ISBN 0-203-16889-5 Master e-book ISBN ISBN 0-203-26418-5 (Adobe eReader Format) ISBN 273 02675 (Print Edition) Contents Preface 1.1 HF Radio: Past and Present Early Developments 1.1.1 Origins of long-range communications 1.1.2 Experiments with the short waveband 1.1.3 HF gains the upper hand 1.2 Changes in Fortune 1.2.1 The reliance upon the operator 1.2.2 The fall from favour 1.2.3 A resurgence of interest 1.3 Present Usage 1.3.1 HF spectrum allocation 1.3.2 Non-military users 1.3.3 Military users 1.3.4 Evolving technology System Considerations Concepts 2.1 2.1.1 The systems approach 2.1.2 System characteristics 2.1.3 Design considerations 10 2.2 Radio Communications Systems 11 2.2.1 System definition 11 2.2.2 System decomposition 12 2.2.3 Open systems interconnection 13 2.2.4 Transmitting sub-system 13 2.2.5 Channel sub-system 14 2.2.6 Receiving sub-system 15 2.2.7 Design considerations 16 2.3 HF Communications Systems 17 2.3.1 Propagation characteristics 17 2.3.2 A unique role for HF 18 iv 2.3.3 System design overview 20 2.3.4 The power level diagram 21 Ground Wave Propagation 23 Propagation over a Plane Earth 23 3.1 3.1.1 Free space propagation 23 3.1.2 Electrical characteristics of the ground 23 3.1.3 Ground wave components 24 3.2 The Surface Wave 24 3.2.1 General principles 24 3.2.2 Zonal relationships 25 3.2.3 Effect of antenna height 26 3.3 The Space Wave 26 3.3.1 Zonal relationships 26 3.3.2 Effect of antenna height 29 3.4 Deviations from Simplified Model 29 3.4.1 General considerations 29 3.4.2 Ground conductivity 30 3.4.3 Terrain irregularities 31 3.4.4 Shadowing 31 3.4.5 Mountainous terrain 32 3.4.6 Vegetation 32 3.5 Field Strength Computation 33 3.5.1 The prediction problem 33 3.5.2 Field strength values 33 3.5.3 Variability of ground conditions 33 3.5.4 Mixed propagation paths 35 3.5.5 Sea state 35 3.5.6 Obstacles 36 3.5.7 Vegetation 37 4.1 Sky Wave Propagation 41 The Ionosphere 41 4.1.1 Structure 41 4.1.2 Ionisation 42 4.1.3 D-region 42 4.1.4 E-region 42 4.1.5 F-region 43 4.1.6 Ionospheric disturbances 43 v 4.2 Wave Propagation in the Ionosphere 44 4.2.1 Physical processes 44 4.2.2 Reflection at oblique incidence 45 4.2.3 Ray paths 46 4.2.4 Virtual height 46 4.2.5 Maximum usable frequency 47 4.2.6 Lowest usable frequency 48 4.2.7 Effect of the Earth’s magnetic field 49 4.3 Variation of the Critical Frequency 49 4.3.1 Typical values 49 4.3.2 Solar cycle dependence 50 4.3.3 Annual, seasonal and diurnal variations 50 4.4 Characteristics of the Received Signal 52 4.4.1 Components 52 4.4.2 Multipath propagation and time dispersion 55 4.4.3 Fading 57 4.4.4 Frequency dispersion 58 4.4.5 Delay distortion 59 4.5 Nearly Vertically Incident Sky Waves 60 4.5.1 The need for short-range sky wave links 60 4.5.2 Selecting the frequency 60 4.5.3 Signal strength 61 4.5.4 Dependence upon range 61 4.5.5 Mode structure and multipath 61 4.5.6 Wave polarisation 62 4.5.7 Summary of attributes 63 Noise and Interference 65 Noise 65 5.1 5.1.1 Sources 65 5.1.2 Noise power 65 5.1.3 Atmospheric noise 66 5.1.4 Man-made noise 67 5.1.5 Galactic noise 67 5.1.6 Statistical variations 67 5.1.7 Condition for external noise limitation 68 5.2 5.2.1 Interference 68 Sources 68 vi 5.2.2 Magnitude of effects 69 5.2.3 Variation with time and frequency 69 5.2.4 Variation with bandwidth 70 5.3 Local Noise and Interference Effects 71 5.3.1 Sources 71 5.3.2 Precipitation static 73 5.3.3 Local electromagnetic interference 73 5.3.4 Electromagnetic compatibility 74 5.3.5 Magnitude of effects 74 5.4 Audio Noise 75 5.4.1 Sources 75 5.4.2 Effects upon speech transmission 75 5.4.3 Effects upon speech reception 75 6.1 System Performance Assessment 76 Antenna Considerations 76 6.1.1 Matching 76 6.1.2 Gain and directivity 76 6.1.3 Polarisation 77 6.1.4 Arrival angles 77 6.1.5 Transmitting antennas 78 6.1.6 Receiving antennas 79 6.1.7 Diversity operation 80 Signal-to-Noise Ratios 81 6.2 6.2.1 The received signal-to-noise ratio 81 6.2.2 The required signal-to-noise ratio 81 6.2.3 The median signal-to-noise ratio 81 6.2.4 Variability of signal-to-noise ratio 82 6.3 Circuit Performance Criteria 83 6.3.1 Ground wave variability 83 6.3.2 Sky wave variability 84 6.3.3 Sky wave availability 84 6.3.4 Circuit reliability factor 85 6.3.5 Effect of signal-to-noise on reliability 85 6.4 Ground Wave Performance 86 6.4.1 Field strength and received power 86 6.4.2 Baseline assessment 87 6.4.3 The range factor 88 vii 6.4.4 6.5 Effect of short antennas Sky Wave Performance 89 91 6.5.1 Representative example 91 6.5.2 Monthly signal-to-noise ratios 92 6.5.3 Frequency dependence 92 6.5.4 Assessment of reliability improvement 93 7.1 Air-Ground Communications 96 The Mobile User 96 7.1.1 Comparison with point-to-point circuits 96 7.1.2 Parameters critical to the mobile user 96 Characteristics of the Airborne Terminal 97 7.2 7.2.1 Antenna radiation efficiency 97 7.2.2 Antenna radiation patterns 98 7.2.3 Aircraft generated noise 99 7.2.4 Flight paths and frequency selection 99 7.3 Impact upon System Performance 100 7.3.1 Effect of antenna efficiency 100 7.3.2 Effect of aircraft noise 100 7.3.3 Effect of frequency choice 101 7.3.4 Effect of flight path 102 7.4 Communications with Small Aircraft 103 7.4.1 Summary of system problems 103 7.4.2 Performance predictions 103 7.4.3 Air-to-ground links 103 7.4.4 Advantage of multi-ground station usage 105 7.4.5 Ground-to-air links 105 7.5 Guidance for the System Designer 107 7.5.1 Criteria 107 7.5.2 Frequency management 109 7.5.3 Antennas 109 7.5.4 Aircraft noise 109 Frequency Management 110 8.1 Techniques 110 8.2 Ionospheric Predictions 110 8.2.1 Predicting the frequency window 110 8.2.2 MUF prediction 111 8.2.3 LUF prediction 112 viii 8.2.4 Example format of long-term predictions 112 8.2.5 Limitations of long-term predictions 113 8.2.6 Short-term predictions 114 8.3 Sounding 114 8.3.1 Types of technique 114 8.3.2 Pulse sounding and ionograms 115 8.3.3 Comparison of sounding techniques 116 8.3.4 Linear sweep sounding (chirpsounding) 118 8.3.5 Channel sounding 119 8.4 Real Time Channel Evaluation (RTCE) 119 8.4.1 The need for RTCE 119 8.4.2 The nature of RTCE 121 8.4.3 Automation of system control 121 8.4.4 Matching the channel to the medium 122 8.4.5 An air-ground link example 122 8.4.6 Potential advantages of RTCE 124 Data Communications 125 9.1 General Considerations 125 9.2 Digital Modulation Techniques 126 9.2.1 Terminology 126 9.2.2 Phase discontinuous schemes 126 9.2.3 Phase continuous schemes 130 9.2.4 Primary modulation schemes for HF systems 131 9.3 Error Rate Performance 132 9.3.1 Error probability 132 9.3.2 Non-fading signals 132 9.3.3 Fading signals 133 9.3.4 Use of diversity reception 134 9.3.5 Non-ideal receivers 135 9.3.6 Effect of non-Gaussian noise 135 9.3.7 Multipath and interference considerations 136 9.4 High Data Rate Transmissions 137 9.4.1 Types of technique 137 9.4.2 Parallel data modulation methods 138 9.4.3 Equalisation techniques 139 9.4.4 Comparison of techniques 140 Wide Bandwidth Techniques 141 9.5 ix 9.5.1 General limitations 141 9.5.2 Channel dispersion effects 142 9.5.3 Matched filter/wideband correlation 142 9.5.4 Matched filter/signal gating 143 9.5.5 Direct sequence spread spectrum 144 9.5.6 Narrowband interference 144 9.6 Principles of Error Control Coding 145 9.6.1 Causes of data errors 145 9.6.2 Types of coding 145 9.6.3 Block coding, with hard decision 146 9.6.4 Convolutional coding, with hard decision 146 9.6.5 Detection and correction of error bursts 147 9.6.6 Soft decision decoding 148 9.7 Performance of Error Control Coding 149 9.7.1 Effect of error probability 149 9.7.2 Coding gain 149 9.7.3 Analysis of examples 149 9.7.4 Some practical considerations 150 9.7.5 Time delays 151 9.7.6 Interleaving 152 9.7.7 Erasure decoding and soft decision decoding 153 10 Impact of Modern Technology 154 10.1 Overview 154 10.2 Hardware Evolution 155 10.2.1 Receivers 155 10.2.2 Transceivers 155 10.2.3 Power amplifiers 156 10.2.4 Synthesisers 156 10.2.5 Transmitting antennas 156 10.2.6 Receiving antennas 157 10.3 Signal Processing 157 10.3.1 Lincompex 157 10.3.2 Digital receive modules 157 10.3.3 Signal detection 158 10.3.4 Signal identification 158 10.3.5 Transmit processing 159 Interference Reduction 159 10.4 REFERENCES [2] [3] [4] [5] [6] 175 R W J Awcock, The lincompex system, Point to Point Communications, pp 130– 142, July 1968 CCIR, Recommendation 455–1, ITU Geneva, 1974 J A Betts, Signal Processing, Modulation and Noise, Hodder and Stoughton, London,1970 M Darnell, Real time channel evaluation, AGARD LS-127: Modern HF Communications, NATO, 1983 D D Falconer and L Ljung, Application of fast Kalman estimation to adaptive equalisation, IEEE Trans Com COM-26, pp 1439–1446, 1978 [7] W Hodgkiss and L F Turner, Practical equalisation and synchronisation strategies for use in serial data transmission over HF links, Radio and Electronic Engineer 53, pp 141–146, 1983 [8] A P Clark and H Y Najdi, Detection process of a 9600 bps serial modem for HF radio links, Proc IEE 130, pp 368–376, 1983 [9] D Chase, A combined coding and modulation approach for communication over dispersive channels, IEEE Trans Com COM-21, pp 159–175, 1973 [10] M Darnell, HF system design principles, AGARD LS-127: Modern HF Communications, NATO, 1983 [11] PAT Hellen, Military secure speech using HF, Electronics and Power, pp 232– 238, IEE, March 1985 Index Page numbers in bold type refer to definitions or section subject headings Absorption 25, 44, 66, 138, 152 atmospheric 90 D-region 57, 59, 82, 114 fading 78 ionospheric 90, 93, 114, 116, 144, 150 polar cap (PCA) 58–60 Acoustic noise 101, 102, 129, 139 Active antenna 110, 214, 215 Adapticom 190–192 Adaptive algorithms 192, 219 arrays 218, 226 beamforming 227 channel evaluation 224 control 168 detection processes 225 equalisation 191, 217, 229 equaliser 225, 226 matched filter 191 modem 174 modulation and coding 227 receive array processing 226 serial techniques 190 system 165, 210, 214 techniques 211, 224 weight calculation 227 ADC, analog-to-digital conversion 211, 215 Aerial-see Antenna Aeronautical mobile 7, AEROSAT AGC, automatic gain control 197, 215 Airborne communications 5, 7, 8, 11, 134 Aircraft antenna 99, 129±132, 137, 147 civil 9, 11, 134 electrical system 98 environment 98, 133 flight path 133, 137, 138 fuselage 99, 101 hull attenuation 101 military 11, 134 noise 101, 133, 136, 144, 147, 148 propeller-driven 99 skin 99, 101 small 131, 139 Aircrew workload 144, 145 Air force 11 Airframe 98, 100, 131 Air-ground communications 2, 5, 129, 130, 138 link 33, 137, 140, 166 Airlines Air traffic control 5, Algorithms, adaptive 192, 219 Aliasing 215 Allocation, spectrum 7, AM, amplitude modulation 11, 171, 172 Amateurs 2, Amplifier 214 Amplitude modulated FM 178 modulation (AM) 11, 171, 172 shift keying (ASK) 171, 174, 180–183, 185 Analog signal 170 Analog-to-digital conversion (ADC) 211, 215 Analytic mode 13 Andeft 189, 191, 192 Angle arrival 105 azimuthal 105, 106 critical 62 diversity 110, 183 elevation 62, 64, 106, 139, 153 grazing 41, 44, 45 incidence 157 phase 79 pseudo-Brewster 105 radiation 105 reflection 42 solar zenith angle 57, 58, 68, 150 Annual variation 69–71 Anomaly, winter 68 Antenna 18, 21, 27, 29, 103 active 110, 214, 215 aircraft 99, 129±132, 137, 147 arrays 211, 218, 226 beamforming 227 Beverage 108 broadband 107, 159, 214 buried 108 characteristics 103 coupler 214, 218, 221 coupling mechanisms 99, 100, 133 directivity 103, 104, 107, 110, 130, 148 diversity 109, 183 effective area 104 176 INDEX effective gain 23 efficiency 22, 28, 29, 92, 103, 104, 108, 110, 116, 119, 129– 131, 135–139, 145, 147, 152, 194 end fed whip 107 feeder 21, 99, 131 gain 22, 23, 41, 103, 104, 107, 110, 127 half wave dipole 107 height 38, 42 horizontal dipole 108, 129 horizontally polarised 109 impedance 103, 106, 214 interference nulling 197, 218, 226 isotropic 104 log periodic 129 loop 110, 133 matching 21, 103, 107, 214 mis-match 22 mobile 119, 214 monopole 107 narrowband 29 noise figure 87–89, 92, 96, 110, 119 notch 133 nulls 211, 218 omni-directional 218 polar diagram 130 polarisation 81, 85, 86, 105 radiation angle 105 radiation patterns 103, 129, 132, 133, 218 radiation resistance 103, 119 reactance 103 receiving 107, 118, 130, 212, 214 resonated 107 rhombic 107, 129 selection 218 self-resonant 107 short 119, 122, 214 siting 130, 131 size 145 spacing 78, 109 steering 145, 226 transmitting 106, 107, 212, 214 transportable 214 travelling wave 107 tuning unit 103, 131, 214 vertically polarised 27, 105, 109 vertical mast 120 whip 107, 122 Appleton, E.V ARQ, automatic repeat request 199, 228 Array—see Antenna array Arrival angle 105 Artificial intelligence 211 ASK, amplitude shift keying 171, 174, 180– 183, 185 Assessor 172, 176 Atmospheric absorption 90 Atmospheric noise 9, 28, 29, 87±91, 139 Attenuation factor 35, 36 hull 101 signal 26, 54, 60, 74 Audio noise 101, 102, 232 Auroral disturbances 59, 152 effects 60, 105 regions 145 zones 59 Automatic gain control (AGC) 197, 215 Automatic repeat request (ARQ) 199, 228 Automatic system control 164, 225 Availability sky wave 115, 138 voice band 94 Avionic installation 99, 148 Azimuthal angle 105, 106 Backscatter 160 Bandwidth 31, 110, 170, 188 correlation 78 limitations 193 maximum 193, 194 receiver 110 reduction 232 signal 219 system 211 transmission 131 wide 170, 193 Barnett, M.A.F Baseline assessment 119 conditions 122 deviation 122 BCH code 204–209 Beamforming 227 Beam system Bearing, great circle 105 BER, bit error rate 179, 189 Binary FM 177 Binary phase shift keying (BPSK) 172, 174, 181–183, 185–187 BIST, built-in self-test 212 BITE, built-in test equipment 211 Bit error rate (BER) 179, 189 Black box 14, 16, 17, 21 Blackout 60 Blanking noise 224 Block 199, 200 codes 199–202 length 202, 206 Blocking 212 Boltzmann constant 87 Boundary height 39 Boundary land-sea 50 sea-land 50, 53 system 14 zone 38 BPSK, binary phase shift keying 172, 174, 181–183, 185–187 Breit, G.2, 63 Brewster angle 105 Broadcasting 9, 129 Built-in self-test (BIST) 211 Built-in test equipment (BITE) 211 Burst errors 198, 201, 203 177 178 HF COMMUNICATIONS: A SYSTEMS APPROACH Business noise 88, 89, 91 Carbon fibre composite 100 CB (citizens band) 10 CCIR 34, 215 atlas 47 noise maps 89 numerical maps 151 predictions 84, 85 Central limit theorem, 112 Channel decoder 23, 24 dispersion 194 encoder 20 evaluation 149, 155, 162, 166 evaluation, air-ground 166 evaluation, real-time 156, 162, 164, 168, 224, 225 sounding 156, 161 sub-system 18–22 transfer function 191 vocoder 230 voice 6, Chip width 196, 197, 222 Chirp 194, 195, 198 Chirpsounding 155, 160, 161 Circuit mobile 10 performance 33, 113 point-to-point 10 reliability 115, 116, 117, 126 transportable 10 Citizens band (CB) 10 Civilian users 6, 9, 11, 134 Clerk Maxwell, J Clipping 192 Closed system 13 Code BCH 204–209 block 199–202 convolutional 199–202 gain 204 Golay 204–209 Hamming 204–209 linear predictive 230 majority vote 204–207 minimum distance 200, 203 Morse 1, 4, 8, 11 Murray 176 rate 200, 204 Reed-Soloman 202, 228 systematic 200 time delay effects 206 Codem 207 Coding error control 166, 169, 198, 199, 203, 206 gain 204 types 198 Coherent detection 171, 180–182, 185, 187 Collisions, electron 25, 57, 60 Command, control, communications (C3) 7, 25 Communications airborne 5, 7, 8, 11, 134 air-ground 2, 5, 129, 130, 138 beyond line of sight 5, 7, 28 data 20, 169, 170 embassy line of sight 5, 28 long range, 1, 27, 141 maritime 2, 4, 7, medium range 141 meteor burst 155, 164, 165 military 6, 10, 11, 134 mobile 119, 129, 193 point-to-point 8, 127, 129, 146, 193 radio 7, 8, 16, 17 reliability 31, 115, 140, 146, 150 satellite 6, 30 ship-shore 1, 4, 10, 11 short range 140 short wave 4–10 strategic 10 success criteria 111 systems 16, 25 tactical 10 wideband 194 Commutator 201 Composite materials 99 Concentration, electron 56±58, 61–63, 67, 79, 82, 114, 115, 149, 152 Conduction current 35 Conductivity, ground 34, 43, 48, 49 Congestion 92, 94, 96, 97 Constraint environmental 130 length 201, 202, 206 mobility 130 physical 130 Continuous phase frequency shift keying (CPFSK) 177, 187 Continuous wave (CW) 8, 11 Convolutional coding 199–202 Correlation bandwidth 78 coefficient 109 distance 78 Cosmic rays 57, 59 Coupling mechanisms 99, 100, 133 CPFSK, continuous phase frequency shift keying 177, 187 Critical angle 62 Critical frequency 58, 62, 66–69, 149, 150 Crystals 5, 212 Curvature of Earth 1, 37, 83 CW, continuous wave 8, 11 Data communication equipment (DCE) 19, 20 communications 20, 169, 170 error rate 77, 109, 155, 179, 198 link 19, 20, 169 link layer 19 modulation 12, 170 INDEX rate 76, 192 shift keying 171 terminal equipment (DTE) 19, 20 transmission 80, 187 Day-to-day variation 69, 114, 115, 151 DCE, data communication equipment 19, 20 Decile values of noise 90, 91, 113 Decision tree 217 Decoder channel 23, 24 medium 23 source 23 24 Decoding erasure 203, 209 hard decision 200 soft decision 203, 209 time delays 206 Defocusing 66, 152 Delay 26, 74 differential 169 distortion 26, 73–76, 80, 194 group 76, 80 line 190, 191, 220 Delta modulation 229 Demodulation coherent 171, 180–182, 185, 187 differentially coherent 187 factor 184, 206 non-coherent 171, 180, 181, 183, 204–207 process 178 Depression, electron density 82 Depth of interleaving 208 of penetration 42, 43 skin 100 Design parameters 24 Detection coherent 171, 180–182, 185, 187 non-coherent 171, 180–185, 204–207 signal 175, 216 Deviation baseline 122 ratio 177, 178 Dielectric constant 34, 48 Differentially coherent demodulation 187 Differential phase shift keying (DPSK) 173, 178–182, 185–189, 192, 195 Diffraction 1, 36, 43, 46 fading 78 knife-edge 43, 46 zone 37–41 Diffuse scattering 45 Digital control 212 filter 190, 210 modulation 170, 173 receive module 215, 216 signal processing (DSP) 189, 210, 212, 227, 229 techniques 217 voice 169, 225, 229 Diplomatic users 179 Dipole electric 34, 48, 118 Hertzian 48, 118 horizontal 108, 129 magnetic 133 moment 48, 118 Direct conversion 215 Directivity of antenna 103, 104, 107, 110, 130, 148 Direct radiation zone 37, 38, 121 Direct sequence spread spectrum 196 Direct voice input 234 Direct wave 35, 40 Dispersion channel 194 frequency 76, 79 spatial 25, 152 time 26, 73±77, 198 Displacement current 35 Distortion delay 26, 73–76, 80, 194 frequency 28 Distribution cumulative 69, 71 normal 90, 111, 112 probability 112 Rayleigh 181 Disturbance auroral 59, 152 ionospheric 58±60 warning 154 Diurnal variation 57, 69, 73, 83 Divergence coefficient 41 Diversity 108, 178, 204, 206, 207 angle 110, 183 antenna 109, 183 combining 225 frequency 183 path 183 polarisation 109, 183 post detection 169 reception 182 space 78, 109, 183 systems 109, 116, 203 time 183, 198, 203 D layer 56, 57, 59, 66, 67, 82, 114 Doppler shift 26, 73, 74, 79, 80, 129, 176, 178, 192 spread 26, 73, 74, 80, 191 DPSK, differential phase shift keying 173, 178–182, 185–189, 192, 195 D-region 56, 57, 59, 66, 67, 82, 114 DSP, digital signal processing 189, 210, 212, 227, 229 DTE, data terminal equipment 19, 20 Dynamic range 212 Earth curvature 1, 37, 83 magnetic field 60, 66 EDC, error detection and correction 199, 225, 228, 230 Effective antenna gain 23 Effective antenna noise factor 87–89, 92, 96, 110, 119 180 HF COMMUNICATIONS: A SYSTEMS APPROACH Effective area of antenna 104 Effective radiated power 111, 119, 123, 146, 168 Efficiency of antenna 28, 29, 92, 103, 104, 108, 110, 116, 119, 129– 131, 135–139, 145, 147, 152, 194 E layer 56, 57, 64, 66, 67, 84, 114, 150 Electrical resonance 131 Electric dipole 34, 48, 118 Electromagnetic compatibility (EMC) 100 emission standards 100 environment 100 interference (EMI) 99 noise 17, 87 pulse (EMP) Electron 56, 57, 87 collision frequency 57 collisions 25, 57, 60 concentration 56±58, 61–63, 67, 79, 82, 114, 115, 149, 152 Electrostatic charging 98 dischargers 101 discharging 98, 148 Element error 179 length 176, 188 Elevation angle 62, 64, 106, 139, 153 ELF, extremely low frequency 28, 56 Embassy communications Embedded data encoding 228 EMC, electromagnetic compatibility 100 EMI, electromagnetic interference 99 E mode 85 EMP, electromagnetic pulse Encoder channel 20 medium 20 source 20 Encryption 228, 233 Entities 19 Envelope detection 171, 183 Environment 14 aircraft 98, 133 electromagnetic 100 noise 130 Equalisation 187, 190, 191 adaptive 191, 217, 229 networks 190 Equaliser 221, 225, 226 Equivalent path 63 vertically incident frequency 157 vertical wave 63 Erasure 209 decoding 203, 209 E-region 56, 57, 64, 66, 84, 114, 150 Error bursts 198, 201, 203 control coding 166, 169, 198, 199, 203, 206 correction 20, 199, 200, 222, 227 detection 20, 199, 200, 222 element 179 function curve 180 probability 179–185, 201, 203–207 random 198 rate 77, 109, 155, 179, 198 Escape ray 62 Ether Evaluation of the channel 149, 155, 162, 166 Exciter 221 Extraordinary wave 66, 74–76, 85 Factor demodulation 184, 206 range 121, 122 shadow 45, 46 Fading 26, 73±77, 116, 209, 227, 229 absorption 78 diffraction 78 effects 109 fast 108, 178, 179 flutter 78, 181 focusing 78 interference 74 pattern 198 polarisation 78 rates 77, 79 Rayleigh 181, 198, 204–207 selective 78, 109, 169, 172, 176, 183, 192, 193, 227 short term 105, 181, 183 signal 180, 205–207 skip 78 Fast Fourier transform (FFT) 216, 217 Fast frequency shift keying (FFSK) 178 FDPSK, frequency differential phase shift keying 189 FEC, forward error correction 199 Feeder lines 21, 99, 131 FFSK, fast frequency shift keying 178 FFT, fast Fourier transform 216, 217 Field strength 34, 40, 43, 47±51, 82–86, 93, 95, 118 Filter adaptive 191 bank 219, 220, 230 crystal 212 digital 190, 210, 217 Kalman 225, 228 matched 190, 191, 194–198 notch 221 pre-modulation 177 simulated 178 F layer 56, 58, 65, 66, 114, 150 F1 layer 56, 58, 64 F2 layer 56, 58, 65–68, 84, 86, 151, 154 Fleming, A Flight paths 133, 137, 138 Flutter fading 78, 181 FM amplitude modulated 178 binary 177 F mode 85 Focusing 66, 114, 152 f0 E 67–70, 150 INDEX f0 F2 67–73, 151, 159 FOR, frequency of optimum reliability 116, 117, 138 Forecast 110, 147, 154, 163 Foreign Office Forest 54 Formant 230 Forward error correction (FEC) 199 FOT, optimum working frequency, 66, 94, 129, 137, 139, 140, 142, 148, 150, 162, 193 Free space propagation 34 F-region 56, 58, 65, 66, 114, 150 Frequency aeromobile 7, aeronautical mobile 7, agility 165, 221 allocation 7, amateur band 27 block 166 broadcasting changing 5, 145 critical 58, 62, 66–69, 149, 150 dependence 125 differential phase shift keying (FDPSK) 189 dispersion 76, 79 distortion 28 diversity 183 electron collision 57 equivalent vertically incident 157 fixed 7, flat fading 169 hopping 170, 194, 210, 213, 221 land mobile lowest usable (LUF) 66, 140, 163, 193 management 144, 147, 149, 168, 217 maritime mobile 7, maximum usable (MUF) 64, 77, 82–86, 93–95, 115, 124, 128, 137, 147, 149–151, 163, 169, 193 mobile modulation (FM) 171, 178 optimum reliability (FOR) 116, 117, 138 optimum working (FOT) 66, 94, 129, 137, 139, 140, 142, 147, 150, 162, 193 planning 134, 149 plasma 61, 67 predictions 30, 147, 149–151 selection 130, 133, 136 selective fading 78, 109, 169, 172, 176, 183, 192, 193, 227 shifting 26, 73, 74, 79, 80, 129, 176, 178, 192 shift keying (FSK) 8, 11, 156, 168, 175– 183, 185–187, 204– 207, 216, 217 spreading 26, 73, 74, 80, 191 standard swept 194, 220 synthesisers 5, 11, 215 tone 175 vertically incident 61 wave 61 window 82, 92, 94, 118, 135, 149, 152, 154, 165 Frequency (cont.) Fresnel zone 42, 45 FSK, frequency shift keying 8, 11, 156, 168, 175–183, 185–187, 204–207, 216, 217 Fuselage 99, 101 Gain antenna 22, 23, 41, 103, 104, 107, 110, 127 code 204 obstacle 46, 52 processing 197, 198 Galactic noise 87±90 Gating 195–197 Gaussian noise 173, 180, 184, 186, 198, 205, 206, 226 ridges 54, 55 Geological structure 44 Geophysical alerts 155 Golay code 204–209 Grazing angle 41, 44, 45 Great circle bearing 105 path 3, 46 Ground-air link 144±146, 167 Ground conductivity 34, 43, 48, 49 electrical characteristics 34 irregularities 157 loss 119 medium dry 48, 49 moisture content 43 reflection loss 105 station 140±145, 148, 166, 168, 194, 226 Ground wave 9–11, 26, 33, 73–76, 81, 85, 89, 105, 132, 146 components 35 performance 118 propagation 34±55, 105 range 114, 123 variability 113 Ground, wet 48–50 Group delay 76, 80 velocity 63 GRWAVE 47, 48 Guard band 186, 188 interval 77 Hamming code 204–209 Handshake message 166, 168 Hard decision decoding 200 Hardware 211 evolution 12, 212 Heaviside.O 1, Height antenna 38, 42 boundary 39 gain factor 38, 39 true 62 virtual 62, 63, 157 Helicopters 11, 99, 101, 102, 148 Hertz, H 181 182 HF COMMUNICATIONS: A SYSTEMS APPROACH Hertzian dipole 48, 118 HF broadcast 11 circuit performance 33 communications systems 25 link performance 103 radio waves 1, 28, 66 signal spectrum 7, 28, 87 High angle ray 62, 76 sky wave 10, 81, 133, 139, 146 High data rate transmission 187 High latitude paths 154 Hopping frequency 170, 194, 210, 213, 221 non-orthogonal 222 orthogonal 222 Horizontal dipole 108, 129 polarisation 26, 39, 42, 85 Hull attenuation 101 Hybrid couplers 213 Identification of signal 216, 217 Impedance antenna 103, 106, 214 free space 118 Imperial wireless chain Impulse response 155, 157, 190, 191, 226 Impulsive noise 87, 169, 184, 198, 205, 209 Incidence angle 157 Incoherent demodulation 171, 180–183, 185, 204–207 Index modulation 116 refractive 47, 60, 61, 79 Induction field 35 Information source 20 transfer 17 Input/output devices 211 Interference 28, 87, 92±101, 109, 136, 139, 145, 161, 164, 167, 169, 184, 209, 218, 226, 232 aeromobile 96 bandwidth dependence 96 baseband 102 blanking 223 broadband 100, 101, 179, 222, 223 burst 228 cancellation 222 congestion 92, 94, 96, 97 directionality 94 discrimination 85 electromagnetic 99 fading 74 frequency dependence 94 impulsive 100 intersymbol 76, 176, 186, 187, 197, 212, 229 local 98, 130 mode 85 models 96, 97 narrowband 96, 97, 101, 102, 192, 197, 220–223 notching 221 nulling at antenna 197, 218, 226 nulling at receiver 197, 219, 226 reduction 211, 218 RF link 92, 102 sources 92 sub-channel 96 time dependence 94 voice band 94 zone 26, 39, 40, 41 Interleaving 202, 208–210, 222, 229 depth 208 matrix 208 Intermodulation 102, 212, 215 products 213, 215 Internal properties 14 Internal receiver noise 87, 90 International Telecommunications Union, ITU Interpolated phase shift keying 189 Intersymbol interference 76, 176, 186, 187, 197, 212, 229 Inverse square law 34 Ionisation 57 Ionograms oblique 80, 157±160 vertical 151, 155±160 Ionosonde 159, 194 Ionosphere 2, 25, 56, 129, 193, 194 Ionospheric absorption 90, 93, 114, 116, 144, 150 characteristics 56–60 disturbances 58–60 forecasting 154 irregularities 25 predictions 149 propagation 60±66 pulse sounding 155 reflection 116 soundings 147, 155 storms 28, 58, 59, 69, 82, 86, 154 tilts 65 wave 26 Irregularities ground 157 ionospheric 25 terrain 44, 121 ISO 7-layer model 19 Isotropic antenna 104 ITU, International Telecommunications Union Jamming 7, 219, 226, 232 Jasik, H 122 Jitter 172 Jungle 81 Kalman filtering 225, 228 Kathryn 190–192 Kennelly, A 1, Keying INDEX amplitude shift (ASK) 171, 174, 180–183, 185 binary phase shift (BPSK) 172, 174, 181– 183, 185–187 coherently detected BPSK (CBPSK) 172, 173 continuous phase frequency shift (CPFSK) 177, 187 data shift 171 differentially encoded BPSK (DEBPSK) 173 differential phase shift (DPSK) 173, 178– 182, 185–189, 192, 195 differential quadrature phase shift (DQPSK) 174, 181, 182, 185, 187 fast frequency shift (FFSK) 178 frequency differential phase shift (FDFSK) 189 frequency shift (FSK) 8, 11, 156, 168, 175± 183, 185–187, 204– 207, 216, 217 interpolated phase shift (IPSK) 189 minimum shift (MSK) 178, 187 multi-amplitude and phase shift (MAPSK) 174, 175 multi-frequency shift (MFSK) 176, 178, 179, 186, 216, 217 multi-phase shift (MPSK) 173, 174, 186, 187 on-off (OOK) 171, 183, 187 phase shift (PSK) 172±176, 180, 191, 192, 198, 217 quadrature amplitude shift (QASK) 174, 175 quadrature phase shift (QPSK) 174, 175, 181, 182, 185–189 time differential phase shift (TDPSK) 188 Kineplex 184, 188, 189, 191, 192 Knife-edge diffraction 43, 46 Knowledge-based systems 234 Land mobile frequency Land-sea boundary 50 Lateral wave 47 Law assessor 172, 176 Layer D 56, 57, 59, 66, 67, 82, 114 data link 19 E 56, 57, 64, 66, 67, 84, 114, 150 F 56, 58, 65, 66, 114, 150 F1 56, 58, 64 F2 56, 58, 65–68, 84, 86, 151, 154 physical 19 Lightning discharges 88 Limited vocabulary speech 210 Lincompex 215 Linear predictive coding (LPC) 230 Linear sweep sounding 155, 160, 195 Link air-ground 33, 137, 140, 166 data 19, 20, 169 ground-air 144±146, 167 point-to-point 8, 119, 127, 129, 146, 193 reliability 137, 139 Long-range communications 1, 27, 141 Long-term forecasts 163 Long wave Loss ohmic 21–23, 104 polarisation 114 power 21, 22 transmission 34, 114 Low angle wave 75, 76 Lowest usable frequency (LUF) 66, 140, 163, 193 183 LPC10 230 LPC, linear predictive coding 230 LUF, lowest usable frequency 66, 140, 163, 193 prediction 151 Magnetic dipole 133 field 60, 66 storms 59, 60, 82 Magneto-ionic components 74–76, 109 Majority vote code 204–207 Man-made noise 28, 87±91, 109 Maps 151, 154 MAPSK, multi-amplitude phase shift keying 174, 175 Marconi, G 1–4 Maritime mobile frequency 7, Martyn, D.F 63 Matched filter 190, 191, 194±198 Matching antenna 21, 103, 107, 214 Maximum bandwidth 193, 194 Maximum usable frequency (MUF) 64, 77, 82–86, 93–95, 115, 124, 128, 137, 147, 149–151, 163, 169, 193 Median MUF 124 Medium decoder 23 Medium dry ground 48, 49 Medium encoder 20 Medium wave 2, 28 Message 17 compression 232 handshake 166, 168 sounding 166 Meteor burst communications 155, 164, 165 reflections 28 MFSK, multi-frequency shift keying 176, 178, 179, 186, 216, 217 Microphone noise cancelling 222 pickup 102 Microprocessor technology 11, 12, 210 Military users 6, 10, 11, 134 Millington, G 50 Minimum distance of code 200, 203 Minimum shift keying (MSK) 178, 187 Mixed propagation paths 50, 121 Mobile communications 119, 129, 193 users 119, 129, 130 Mode analytic 13 arrival angle 110 propagation 74±76, 129, 153, 169 separation 110 sky wave 73±76, 106, 129, 139, 153, 183 structure 85 synthetic 13 Modem 170, 194 adaptive 174 multi-tone 5, 183, 190 parallel data 190, 191 serial data 192 Modulating signal 21, 172–175 184 HF COMMUNICATIONS: A SYSTEMS APPROACH Modulation adaptive 227 amplitude 11, 171, 172 data 12, 170 delta 229 digital 170, 173 frequency 171, 178 index 116 phase 171 pulse code (PCM) 229 scheme 31 spectrum 177 spread spectrum 170, 196, 222, 223, 228 technique 169, 179 wideband 170, 193, 210, 221 Modulo-2 adder 201 Moisture content 43 Morse code 1, 4, 8, 11 Mountainous terrain 46 MPSK, multi-phase shift keying 173, 174, 184, 187 MSK, minimum shift keying 178, 187 MUF, maximum usable frequency 64, 77, 82–86, 93–95, 115, 124, 128, 137, 147, 149–151, 163, 169, 193 factor 64, 65 prediction 150 Multi-amplitude phase shift keying (MAPSK) 174, 175 Multi-frequency shift keying (MFSK) 176, 178, 179, 186, 216, 217 Multi-ground stations 142 Multi-hop paths 74, 75 Multipath 75±77, 85, 86, 109, 114, 129, 178, 179, 184, 186–198, 226 Multi-phase shift keying (MPSK) 173, 174, 186, 187 Multiplexing 187 Multi-tone modems 5, 183, 190 Multi-tone systems 77, 172, 179, 188, 191 Murray code 176 Narrowband interference 96, 97, 101, 102, 192, 197, 220–223 Navy 10 Nearly vertically incident skywave (NVIS) 27, 81±86 Network sounding 159 Noise 30, 87, 103, 109, 110 acoustic 101, 102, 129, 139 aircraft generated 101, 133, 136, 144, 147, 148 atmospheric 9, 28, 29, 87±91, 139 audio 101, 102, 232 blanking 224 broadband 102 bursts 206 business 88, 89, 91 cancelling microphone 222 day-to-day variability 90 decile values 90, 91, 113 discrimination 130 effective antenna 87±89, 92, 96, 110, 119 electrical 129, 139 electromagnetic 17, 87 environment 130 external 92 field strength 88 figure 87±89, 92, 96, 110, 119 frequency dependence 89 galactic 87–90 Gaussian 173, 180, 184, 186, 198, 205, 206, 226 impulsive 87, 169, 184, 198, 205, 209 local 98 long-term characteristics 87 man-made 28, 87±91, 109 maps 89 non-Gaussian 87, 184, 198 performance 213 power 87, 88, 92, 111, 119, 125, 130 power distribution 90 quiet rural 88, 89, 91 receiver 87, 90 residential 88–91 rural 88–91, 119 short-term characteristics 87 sources 87 thermal 17, 23, 87 variability 114 Noise (cont.) Nomogram 53 Non-coherent detection 171, 180–185, 204– 207 Non-fading signals 180, 181, 205 Non-Gaussian noise 87, 184, 198 Non-ideal receivers 184 Non-military users Normal distribution 90, 111, 112 Notch antenna 133 filter 221 Null antenna 211, 218 Numerical mapping 151, 154 NVIS, nearly vertically incident sky wave 27, 81±86 Nyquist rate 188 Oblique chirpsounder record 161 incidence backscatter 156–160 incidence sounding 156, 157, 159, 194 incident wave 60, 62 ionogram 80, 157±160 path 62 reflection 60–62 Obstacle gain 46, 52 Obstacles 44, 52, 81, 121 Occupancy of spectrum 96, 178 Off-line analysis 163 Ohmic losses 21–23, 104 On-off keying (OOK) 171, 183, 187 Open system 13, 14 Open systems interconnection (OSI) 18, 19 Operator experience 5, skill 6, 11, 158 Optimum working frequency (FOT) 66, 94, 129, 137, 139, 140, 142, 147, 150, 162, 193 Ordinary wave 66, 74, 85 OSI, open systems interconnection 18, 19 Ott, R.H, 47, 53 Outputs 14 Over-the-horizon radar 79, 194 INDEX Parallel data modems 190, 191 data transmission 187, 188, 192 Parity bits 200 Path equivalent 63 great circle 3, 46 loss 22, 52, 110, 130 oblique 62 propagation 30, 76, 118 ray 61±63, 76, 79, 80, 114, 158 virtual 63 PCA, polar cap absorption 58–60 PCM, pulse code modulation 229 Peak power limitation 188, 192 Peak-to-mean ratio 188, 192 Penetration depth 42, 43 Phase angle 79 continuous modulation 177 difference 35, 40, 44 discontinuous modulation 171 jitter 172 lock loop 213 modulation 171, 177 shift keying (PSK) 172–176, 180, 191, 192, 198, 217 Phased antenna arrays 211, 218, 226 Physical constraints 130 Physical layer 19 Piccolo 176 Plasma frequency 61, 67 Point-to-point link 8, 119, 127, 129, 146, 193 Polar cap absorption (PCA) 58–60 Polar diagram 130 Polarisation 27, 60, 105 antenna 81, 85, 86, 105 coupling loss 85 diversity 109, 183 fading 78 horizontal 26, 39, 42, 85 loss 114 mis-match 22, 25, 104 vertical 26, 27, 39, 42, 48, 85, 133 wave 23, 85, 105 Post detection diversity 169 Power amplifier 131, 213, 218 gain 103 level 165 level diagram 31–33 loss 21, 22 noise 87, 88, 92, 111, 119, 125, 130 radiated 111, 119, 123, 146, 165, 168 received 22, 118 spectrum 77 Precipitation static 99 Prediction accuracy 154, 163 errors 154 field strength 47 frequency 30, 147, 149–151 185 ionospheric 149 limitations 153 long-term 149, 152, 153, 154 LUF 151 MUF 150 off-line 162 propagation 5, 151 short-term 149, 154 PRN, pseudo-random noise 195 Probability distribution 112 of errors 179–185, 201, 203–207 Processing gain 197, 198 Propagation 25±27, 34–55, 56–86 anomalous 155 forecasts 110, 147, 154 free space 34 ground wave 34±55, 105 ionospheric wave 60±66 medium 18, 21 mixed path 50 mode 74±76, 129, 153, 169 multipath 75±77, 85, 86, 109, 114, 129, 178, 179, 184, 186–198, 226 off-line analysis 162 path 30, 76, 118 path loss 33 prediction 5, 124, 162 sky wave 3, 56, 105, 115, 124, 193 Propeller effects 99 Pseudo-Brewster angle 105 Pseudo-random noise (PRN) 195 Pseudo-random sequence 222, 223 PSK, phase shift keying 172–176, 180, 191, 192, 198, 217 Pulse code modulation (PCM) 229 compression coding 159 sounding 155, 156, 159 QAM, quadrature amplitude modulation 174 QASK, quadrature amplitude shift keying 174, 175 QPSK, quadrature phase shift keying 174, 175, 181, 182, 185–189 Quadrature amplitude modulation (QAM) 174 amplitude shift keying (QASK) 174, 175 phase shift keying (QPSK) 174, 175, 181, 182, 185–189 Quiet rural noise 88, 89, 91 Radiated field 36 Radiated power 111, 119, 123, 146, 165, 168 Radiation angle 105 efficiency 22, 28, 29, 92, 103, 104, 108, 110, 116, 119, 129– 131, 135–139, 145, 147, 152, 194 patterns 103, 129, 132, 133, 218 resistance 103, 119 solar 57 Radio amateurs 2, communication 7, 8, 16, 17 186 HF COMMUNICATIONS: A SYSTEMS APPROACH control 233 horizon 42 horizon zone 39–41 regulations spectrum 24 telegraphy 4, telephony 4, waves 1, 21, 25, 34–42, 57–66 Ralphs, J.D 179 Random errors 198 Range dependence 64, 65, 84 factor 121, 122 reduction coefficient 52, 53 Rank 19 Ray cosmic 57, 59 escape 62 high angle 62, 76 path 61±63, 76, 79, 80, 114, 158 skip 62, 64 theory 41, 61 ultra violet 57, 59 X 57, 59 Rayleigh criterion 45 distribution 181 fading 181, 198, 204–207 Real time channel evaluation (RTCE) 156, 162, 164, 168, 224, 225 Receive modules, digital 215, 216 Receiver 18, 23, 211, 212, 224 bandwidth 110 dynamic range 212 frequency-agile 212 front-end 212 ideal 180 interference nulling 197, 219, 226 noise figure 90, 92 non-ideal 184 response sensitivity 23, 66 Receiving antenna 107, 108, 130, 212, 214 antenna array 211, 218, 226 sub-system 18, 19, 23 Reciprocal mixing 24, 212, 213 Recognition speech 210, 231–234 voice 210, 231–234 word 231 Recovery effect 50, 53 Reed-Soloman coding 202, 228 Reference atmosphere 47 curves 48 radiator 48 Reflected wave 35, 40 Reflection angle 42 coefficient 35, 41, 42, 45 oblique 60–62 specular 45 Refraction 61 tropospheric 41, 47 Refractive index 47, 60, 61, 79 Regulations Relative permeability 34 Reliability 31, 115, 116, 117, 126, 135, 140, 146, 147, 150, 226 improvement 127, 128, 136 Residential noise 88–91 Resonance 131 RF interference 92, 102 Ridges 46 Ringing 212 Rotor blade effects 99 Rough sea 52 surface 45 RTCE, real time channel evaluation 156, 162, 164, 168, 224, 225 Rural noise 88–91, 119 Rutherford-Appleton laboratory 67 Satellite communications 6, 30 links 30 vulnerability 6, Scatter process 66 tropospheric 29, 46 Scattering, diffuse 45 Scrambler 233 Screening 29 Sea-land boundary 50, 53 Seasonal variation 57, 69, 72 Sea state 52 water 48–52 Secant law 64 Secure digital voice 169, 225, 229 Secure speech 233 Selective fading 78, 109, 169, 172, 176, 183, 192, 193, 227 Selective nulling 220 Sensitivity 23, 66 Serial data modem 192 Settling time 213 Shadow factor 45, 46 Shannon, C.E 170, 229 Shift keying, see Keying Ship-shore communications 1, 4, 10, 11 Short antennas 119, 122, 214 Short-term fading 105, 181, 183 Short-term forecasting 154, 163 Short-term prediction 149, 154 Short wave broadcasting 4, communications 4–10 SID, sudden ionospheric disturbance 58, 59, 162 Signal analog 170 attenuation 26, 54, 60, 74 bandwidth 219 broadband 217, 224 INDEX detection 175, 216 fading 180, 205–207 gating 195–197 identification 216, 217 modulated 172–175 modulating 21, 172–175 non-fading 180, 181, 205 processing 210, 211, 215 processing algorithms 168 received 73 strength 82 wideband 194 Signal-to-noise criterion 111 density 120, 140–143 instantaneous 111 median 111, 116, 125, 139, 140, 141, 152 predicted 125 ratio 30, 31, 85, 92, 104, 107, 110, 122, 127, 150, 152, 153, 161, 165, 170, 179.184, 194, 198, 226 received 110, 128, 129 required 111, 126 standard deviation 112 variability 111 Silent zone 26 Simulated filtering 178 Simultaneous operation 212 Single sideband (SSB) 5, 8, 11, 212 Skin depth 100 Skip distance 26, 27, 62 ray 62, 64 Sky wave 2, 10, 26, 31, 33, 56, 73±76, 82, 85, 89, 92, 105, 132, 229 availability 115, 138 high angle 10, 81, 133, 139, 146 mode 73±76, 106, 129, 139, 153, 183 nearly vertically incident 27, 81±86 performance 124 propagation 3, 56, 105, 115, 124, 193 variability 114 Slough measurements 67 Smooth surface 45 Snell’s law 61 Soft decision decoding 203, 209 Solar cycle 57, 67, 69, 149 flare 58, 59, 80 flux forecasts 155 proton events 60 radiation 57 X ray flare 59 zenith angle 57, 58, 68, 150 Solid state components 212 Sommerfeld theory 37, 47 zone 37, 38, 121 Sounding 149, 150, 155, 166 channel 156, 161 chirp 155, 160, 161 cycle 167 frequency 167 ionospheric pulse 155 linear sweep 155, 160, 195 message 166 network 159 oblique incidence 156, 157, 159, 194 oblique incidence backscattrer 156–160 pulse 155, 156, 159 transmission 167 vertical incidence 155–161 Source decoder 23, 24 encoder 20 Space diversity 78, 109, 183 wave 35, 38, 39 Spectral analysis 220 occupancy 96, 178 pollution 168 purity 211, 213 Spectrum allocation 7, efficiency HF 7, 28, 87 modulation 177 monitor 160 occupancy 96, 178 power 77 radio 24 spread 170, 196, 222, 223, 228 Specular reflection 45 Speech connected 231 degradation 102 intelligibility 102, 155, 219 limited vocabulary 210 processing 211, 229, 232 reception, noise effects 102 recogniser 229, 230, 234 recognition 210, 231–234 scrambler 233 secure 233 synthesis 169, 230, 232, 234 transmission, noise effects 102 waveform 230 Sporadic E 57, 58, 69, 81, 86, 114, 115, 154, 161, 162, 164 Spread F 77, 80 Spread spectrum 170, 196, 222, 223, 228 SSB, single sideband 5, 8, 11, 212 Standard deviation 90, 112 Standard frequency Standing wave ratio 106, 107, 131 Storms ionospheric 28, 58, 59, 69, 82 magnetic 59, 60, 82 Sub-system 15, 16 channel 18–22 entities 19 optimisation 16 performance 16 187 188 HF COMMUNICATIONS: A SYSTEMS APPROACH receiving 18, 19, 23 transmitting 18–20 Sub-system (cont.) Sudden ionospheric disturbance (SID) 58, 59, 162 Sunrise 79 Sunset 79 Sunspot activity 67, 69, 82, 95, 137 cycle 67, 149, 153 maximum minimum number 57, 67, 68 Surface objects 44 rough 45 smooth 45 wave 10, 35, 36, 38 Swept frequency signal 194, 220 Symbol 170, 171, 176, 179, 202, 226 boundary 171 period 186 synchronisation 159, 173, 176, 189, 194– 197, 222, 230 Synthesised speech 169, 230, 232, 234 Synthesiser 213 digitally controlled 210, 212, 221 direct 213 frequency 5, 11, 215 indirect 213 Synthetic mode 13 System 13 adaptive 165, 210, 214 approach 13 bandwidth 211 boundary 14 characteristics 13 closed 13 control automation 164, 225 decomposition 18 design 15, 16, 30 engineering 15 environment of 14 HF communication 25 inputs 14 knowledge-based 234 multi-tone 77, 172, 179, 188, 191 open 13, 14 optimisation 16 outputs 14 performance 15, 103, 111, 135 power loss 21 problems 139 radio communications 16–18 trade-off 15 viewpoint 24 Systematic code 200 effects 43 Temporal variation 115, 149, 151 Terrain 26, 43–17 features 43 independent coverage 81 irregularities 44, 121 mountainous 46 roughness 45 wooded 44, 46 Theoretical models 30 Thermal noise 17, 23, 87 Thermionic valve Threshold detector 171 Time compression 194 delays in coding 206 differential phase shift keying (TDPSK) 188 dispersion 26, 73±77, 198 diversity 183, 198, 203 gating 195–197 Tone frequencies 175 separation 189 Trade-off analysis 15 Training sequence 190 Transceiver 211, 212 Transmission line 18, 21 loss 34, 114 parallel data 187, 188, 192 Transmit processing 218 Transmitter 18, 20 power 129, 225 Transmitting antennas 106, 107, 212, 214 Transmitting sub-system 18–20 Tropospheric refraction 41, 47 scatter 29, 46 True height 62 Tuned circuit 131 Tuning automatic 11 speed 211, 213, 221 unit 103, 131, 214 Tuve, M.A 2, 63 Tamed frequency modulation 178 Tapped delay line 190 Technology 11, 210 Telemetry 199 Temperature coefficient 43 Vacuum tubes 5, 213 Variation annual 69–71 day-to-day 69, 90, 114, 115, 151 diurnal 57, 69, 73, 83 UHF, ultra high frequency 5, 10, 184 Ultra violet 57, 59 Users civilian 6, 9, 11, 134 diplomatic military 6, 10, 11, 134 mobile 119, 129, 193 non-military INDEX night-time 151 seasonal 57, 69, 72 temporal 115, 149, 151 Vegetation 46, 54, 121 Velocity, group 63 Vertical incidence sounding 155–161 incident frequency 61 ionogram 151, 155±160 polarisation 26, 27, 39, 42, 48, 85, 133 sounding 155–161 steerable array 110 wave 63 Very high speed integrated circuitry (VHSIC) 211 Very large scale integration (VLSI) 11, 210, 215, 226, 232 VHF, very high frequency 5, 10, 28, 87, 184 VHSIC, very high speed integrated circuitry 211 Vietnam 10 Virtual height 62, 63, 157 Virtual path 63 Viterbi algorithm 226 VLF, very low frequency 56 VLSI, very large scale integration 11, 210, 215, 226, 232 Vocabulary, word 229 Vocoders 229–234 channel 230 Voice band availability 94 channels 6, digitisation 229 input 234 intelligibility 116 processing 210 recognition 210, 231–234 templates 232 Voltage standing wave ratio (VSWR) 106, 107, 131 Wave direct 35, 40 equivalent vertical 63 Extraordinary 66, 74–76, 85 frequency 61 front 36 ground 9–11, 26, 33, 73–76, 81, 85, 89, 105, 132, 146 high angle 10, 62, 76, 81, 133, 139, 146 ionospheric 26 lateral 47 long low angle 75, 76 medium 2, 28 obliquely incident 60, 62 Ordinary 66, 74, 85 polarisation 23, 85, 105 propagation 25–27, 34–55, 56–86 radio 1, 21, 25, 34–42, 57–6 reflected 35–40 short 4–10 sky 2, 10, 26, 31, 33, 56, 73±76, 82, 85, 89, 92, 105, 132, 229 space 35, 38, 39 surface 10, 35, 36, 38 Waveband medium 2, 28 short 2, 4–10 Wet ground 48–50 Wideband correlation 194 signal 194 Wide bandwidths 170, 193 Window, frequency 82, 92, 94, 118, 135, 149, 152, 154, 165 Winter anomaly 68 Wireless telegraphy Wooded terrain 44, 46 Word recognition 231 vocabulary 229 Workload 144, 145 Worldwide noise maps 89 WWV, Fort Collins 154 X ray 57, 59 Zenith angle, solar 57, 58, 68, 150 Zero IF 215 Zonal relationships 36, 39 Zone auroral 59 boundary 38 diffraction 37–41 direct radiation 37, 38, 121 Fresnel 42, 45 interference 26, 39, 40, 41 radio horizon 39–41 silent 26 Sommerfeld 37, 38, 121 Zurich sunspot number 152 189 [...]... World War communications with aircraft were almost entirely by HF, and commonly employed handoperated Morse, although the first trials of air-ground voice communications had been made in the US as early as 1928 The Second World War saw the development and introduction of VHF and UHF for airborne communications However, since these frequency bands were constrained by line-of-sight propagation, any communications. .. continued to require the use of frequencies in the HF band Just after the end of the War, before VHF air traffic control communications were fully implemented, air-to-ground communications were conducted using frequencies between 3 and 6 MHz and ground-to-air communications at about 300 kHz Where air-to-ground communications ranges of about 50 km were desired, communications were often found to be very poor,... normal VHF nets Satellite communications are still too expensive to contemplate for general widespread use on the battlefield; their vulnerability is also a cause for concern The traditional VHF/UHF links are unable to cope with beyond-line-of-sight communications requirements For all practical purposes UHF is limited to line-of-sight and can be successfully operated only when there is visual contact VHF,... better than UHF in this respect, also suffers from screening difficulties The only reliable means of communications must make use of surface waves or short-range sky waves Such communications can best be accomplished by use of the low frequency end of the HF band For example man-portable HF- SSB transceivers are sometimes more useful than VHF sets, particularly in thick jungle or rough terrain HF was extensively... circumstances VHF meteor reflections are reliable for low rate data but have approximately the same 1800 km range limitation Frequencies in the VHF band and above are primarily limited to line-of-sight communications For all practical purposes UHF can only be operated successfully when there is visual contact VHF, though better than UHF in this respect, also suffers from screening difficulties HF signals... overcome many of the traditional problems that have plagued the HF communications system designer The aim of this book is to provide a firm foundation for the design, evaluation and operational use of HF communications The subject is approached from the systems viewpoint; it is the systems issues relating to communications within the HF band that are primarily of concern It is intended that the book... problems, typical of airborne HF communications, are examined later in Chapter 7 The HF band was now firmly established as the primary means of beyond line-of-sight communications Pioneers of radio concentrated their long-range experiments in the HF band This effort brought about a continuing stream of refinements in technology that, in turn, improved the level of attainable HF performance Some of the... have much shorter communications range requirements to their bases but are nonetheless beyond-line-of-sight Support helicopters pose still shorter communications requirements of tens of kilometres to the supported ground troops The rugged nature of the terrain again necessitates the use of the HF band to effect contact with the tactical ground communications nets in these regions 8 HF COMMUNICATIONS: ... marriage of computer technology with HF communications systems offers tremendous promise to improve performance and reliability The quantum leap in microprocessor technology has coincided with the resurgence of interest in the HF band, promising to revolutionise the HF world The focus has been on using the best new technologies to overcome the traditional weaknesses of HF communications In particular, the... exclusive domain of communications engineers Today the systems analyst and designer of computer-based systems must have a considerable appreciation of the technical principles of the wide range of communications techniques The resurgence of interest in the HF band has meant that many new systems being proposed are incorporating HF links HF is a vital ingredient in the strategic mix of communications media ... with HF make it essential that today’s systems designer has a fundamental appreciation of HF communications 2.3 HF Communications Systems 2.3.1 Propagation Characteristics Propagation in the HF. .. development and introduction of VHF and UHF for airborne communications However, since these frequency bands were constrained by line-of-sight propagation, any communications link to the aircraft... require the use of frequencies in the HF band Just after the end of the War, before VHF air traffic control communications were fully implemented, air-to-ground communications were conducted using