NAB Uplink Operator SeminarR9

5/24/2018 NAB Uplink Operator SeminarR9

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October,2006

By:NormanWeinhouse

and

SidneySkjei,P.E.

Skjei Telecom, Inc.7777 Leesburg Pike, Suite 315N

Falls Church, Virginia 22043

Phone: 703-917-9167Email: [email protected]

www.skjeitelecom.com

NAB SATELLITE UPLINK OPERATORS TRAINING COURSE

TEXT AND CLASSROOM NOTES


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October, 2006

By: Norman Weinhouse

andSidney Skjei, P.E.

Skjei Telecom, Inc.7777 Leesburg Pike, Suite 315N


Phone: 703-917-9167Email: [email protected]

www.skjeitelecom.com

NAB SATELLITE UPLINK OPERATORS TRAININGCOURSE

TEXT AND CLASSROOM NOTES


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COPYRIGHT 2006

Skjei Telecom, Inc.

7777 Leesburg Pike, Suite 315N


703-917-9167

All rights reserved. No part of this text may be reproduced or utilized in any formor by any means, electronic or mechanical, including photocopying, recording, or byinformation storage and retrieval systems, without permission in writing from SkjeiTelecom, Inc.


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Copyright 2006 ii All rights reserved

TABLE OF REVISIONS

RevisionNo.

Purpose/changes Author Date

R0.1 Initial Release Norman

Weinhouseand SidneySkjei

May 5,

2006

R9 Update Sidney Skjei Sept,2006


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Copyright 2006 iii All rights reserved

Table of Contents

CHAPTER 1: INTRODUCTION 1

BRIEFHISTORYOFCOMMUNICATIONSATELLITESINU.S. 2INTERNATIONAL SERVICE 7

CHAPTER 2: BASIC CONCEPTS 9

DECIBEL NOTATION 9DIRECTIONAL ANTENNAS 10

ANTENNA GAIN 10RADIATION PATTERN 11

GEOSTATIONARY ORBIT 12SATELLITE LAUNCH SEQUENCE 13SATELLITE VISIBILITY FROM EARTH 14

SUN OUTAGES 17ANGULAR DISTANCE BETWEEN SATELLITES 19

FREQUENCY/POLARIZATION PLANU.S.DOMESTIC 19TRANSPONDERS AND FREQUENCIES 19POLARIZATION 20CBAND 22KU BAND 23

THE COMMUNICATION SATELLITE 24SPACECRAFT BUS 25

Stabilization and Station Keeping 25Power 27Propulsion 28

Telemetry and Control 30THE COMMUNICATIONS PAYLOAD 30

Wideband Receiver 31Channelization 33Antenna Subsystem 36

SATELLITE CHARACTERISTICS (FOOTPRINTS) 38SATURATION FLUX DENSITY (SFD,AND G/T) 38EFFECTIVE ISOTROPIC RADIATED POWER (EIRP) 42

NOISE 43THERMALNOISE 43ANTENNANOISE 45RECEIVERNOISE TEMPERATURE (CLEAR WEATHER) 46

POWER ADDITION OFNOISE 48SATELLITE ACCESS METHODS 48

LINKS AND NETWORKING 51ONE WAY (BROADCAST)LINKS 51TWO WAY (BIDIRECTIONAL)LINKS 52

Point to Point Links 52Networks 52


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Mesh Networks 53Star Networks 54Factors in Choosing a Network Type 55

THE EARTHSATELLITE LINK 55POWER CONSIDERATIONS IN THE UPLINK 55UPLINK THERMAL CARRIER TONOISE RATIO 56

INTERFERENCE IN THE UPLINK 57Antenna Sidelobe Discrimination 57Uplink Carrier to Interference Ratio 58

THE SATELLITEEARTH LINK (DOWNLINK) 63DOWNLINK THERMAL CARRIER TONOISE RATIO 63DOWNLINK CARRIERTO-INTERFERENCE RATIO 66

CARRIER-TO-INTERMODULATION RATIO 67INTERFERENCE LOCATION SYSTEMS 69AGGREGATION OF INTERFERENCE EFFECTS 71

PROPAGATION ANOMALIES 72WEATHER RELATED FACTORS IN SATELLITE LINKS 72

Effects of Rain 73

Rain Attenuation 73Noise Temperature Effects 73Depolarization 75Uplink and Downlink Effects and Countermeasures 75

Uplink Effects and Countermeasures...................................................................76Downlink Effects and Countermeasures..............................................................76

Scattering 76Effects of Snow 76

OTHER PROPAGATION ANOMALIES 77OVERALL PREDETECTION CARRIER-TO-NOISE RATIO 77CHARACTERISTICS OF C,KU AND KA BAND SATELLITE COMMUNICATIONS 78

C-BAND SATELLITES 78KU-BAND SATELLITES 78KA-BAND SATELLITES 79COMPARISON OF C,KU AND KA BAND SYSTEMS 81

COMMONLY USED MODULATION TECHNIQUES 83FREQUENCY MODULATION 83

TelevisionFM/TV 83Frequency Division Multiplex, FDM/FM 84Single Channel Per CarrierSCPC/FM 84

DIGITAL MODULATION 84SPREAD SPECTRUM 85OVERMODULATION 85

SIGNAL-TO-NOISE RATIO-ANALOG SYSTEMS 86

FMTELEVISION 86Video-Signal-to-Noise Ratio 86Audio-Signal-to-Noise Ratio 89

FM Subcarriers 89Sound in Synch Digital Audio 91

FMSCPC 92FDM/FM FMSUBCARRIERS 92


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FDM/FMSINGLE SIDEBAND SUBCARRIERS 93DIGITAL TECHNOLOGIES 93

SOURCE CODING (BASEBAND PROCESSING) 94Pulse Code Modulation (PCM) 94Predictive Techniques 94Forward Error Correction 95

DIGITAL MODULATION TECHNIQUES 95Amplitude, Phase and Symbols 95Biphase Modulation (BPSK) 97Quaternary Phase Modulation (QPSK) 99

SIGNAL-TO-NOISE RATIO AND EB/NO 1028PSKAND 16QAMMODULATION 104COFDMMODULATION 106FORWARD ERROR CORRECTION CODING 107

Block Coding 107LDPC 108

Convolutional Coding 110System Impairments 113

Eye Patterns 114COMPRESSED DIGITAL TELEVISION AND TRANSMISSION 114

INTRODUCTION-ANALOG TELEVISION 114TYPES OF VIDEO 116INTRODUCTION TO DIGITAL VIDEO 117WHY DIGITAL TELEVISION? 117WHY COMPRESSION? 118DIGITAL TELEVISIONBASICS 118

The A-D ProcessSampling, Quantizing and PCM Coding 119Sampling 119Quantizing 120Encoding 121

Serial or Parallel Transmission 123COMPRESSION 123

Compression Techniques 126Pre-Processing and Redundancy Removal 126Prediction and Motion Compensation 126TransformationFrequency Decomposition 127Quantization 127Entropy Reduction 128

ALGORITHMS 128DECOMPRESSIONDECODING 131COMPLETE SYSTEM EXAMPLE 133STANDARDIZATION 133

CURRENT STANDARDS FOR SATELLITE TRANSMISSION OF DIGITAL TELEVISION 134DIGITAL TELEVISION STANDARD (DVB) 135

DVB-S and DVB-S2 136EMERGING ENCODING METHODS:MPEG4AND JPEG2000 137

MPEG 4 Part 10 and SMPTE VC-9 137JPEG 2000 138

HIGH DEFINITION TELEVISION 140


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ADVANCED TELEVISION STANDARDS COMMITTEE (ATSC) 140SATELLITE TRANSMISSION OF COMPRESSED TELEVISION 142HIGH DEFINITION (HD)TRANSMISSION OVER SATELLITE 145DIRECT BROADCAST SATELLITE SYSTEMS 145

CHAPTER 3: GROUND EQUIPMENT 147

UPLINK GROUND COMMUNICATIONS EQUIPMENT 149Television Exciters/Uplink Video Equipment 149

Analog Exciter 149Baseband Circuits 149Modulation and Upconversion 150Transmitter Identification 151

Digital Exciter 152SCPC Uplinks 152

POWER AMPLIFIERS 154MULTIPLEXERS AND SWITCHES 156

Switches 156Multiplexers 156Satellite SimulatorNon Radiation Tests 159

DOWNLINK EQUIPMENT 160LOWNOISE AMPLIFIERS/CONVERTERS 160POWER DIVIDERS 163DOWNCONVERTER/DEMODULATOR 164INTEGRATED DIGITAL RECEIVER-DECODER 164

ANTENNAS,DUPLEXER AND IFL 164DUPLEXER 165ANTENNASRADIATING ELEMENTS 166

Gain and Sidelobe Performance Verification 166

Antenna GeometryFeed Systems 166Mechanical Features 168

Dimensional Tolerances 169Foundations, Mounts and Motor Drives 169

RECEIVE ONLY EARTH STATION 170INTERFACILITY LINK (IFL) 170

POWER SYSTEMS 171MAINTENANCE PROGRAMS 171EARTH STATION LICENSING 172

FREQUENCY COORDINATION 174

CHAPTER 4: UPLINK OPERATION 175

OPERATING RESPONSIBILITIES 175OPERATOR CONTROLS 176TEST EQUIPMENT AND CALIBRATION 176ACCESS PROCEDURES 177

ESTABLISH CONTACT WITH SATELLITE OPERATORS 177LOCATE AND VERIFY IDENTITY OF PROPER SATELLITE 177


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ANTENNA OPTIMIZATION AND PRE-TRANSMISSION ADJUSTMENTS 178TRANSMISSION 178

SATELLITE NEWS VEHICLES(SNG) 178EVOLUTION OF SNGVEHICLES 179PERTINENT DOTREGULATIONS 180ANALOG OR DIGITAL 180

VOICE COMMUNICATIONS 181SNGPRIORITIES 182

SAFETY 182MICROWAVE RADIATION HAZARDS 182POWER AMPLIFIER AND POWER SUPPLY 183EQUIPMENT LAYOUT AND HOUSEKEEPING 183

INTERFERENCE MANAGEMENT 183REVIEW OF COMMON OPERATOR ERRORS 184REVIEW OF CRITICAL EQUIPMENT ITEMS 184

REFERENCES 185

APPENDICES 186


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Table of FiguresFIGURE 1-1 WORLDWIDE SATELLITE COORDINATION.................................................................... 3FIGURE 1-2: U.S. DOMESTIC SERVICE................................................................................................... 5FIGURE 1-3: FREQUENCY BAND NOMENCLATURE ........................................................................... 6FIGURE 1-4: ATMOSPHERIC ATTENUATION AT DIFFERENT FREQUENCY BANDS.................... 7

FIGURE 2-0 QUICK REFERENCE LIST OF DECIBELS........................................................................... 9FIGURE 2.1 ILLUMINATION OF A PARABOLIC REFLECTOR .......................................................... 12FIGURE 2-2 GEOSTATIONARY SATELLITES....................................................................................... 13FIGURE 2-3: SATELLITE LAUNCH SEQUENCE.................................................................................. 14FIGURE 2-4: NORTH AMERICAN MAGNETIC DECLINATION ......................................................... 15FIGURE 2-5 GROUND ANTENNA ELEVATION AND AZIMUTH FOR STATIONARY SATELLITES

............................................................................................................................................................. 16FIGURE 2-6: GEOMETRY OF SUN OUTAGE......................................................................................... 18FIGURE 2-7: LINEAR POLARIZATION OF RADIATION FROM VERTICALLY AND

HORIZONTALLY POLARIZED FEED HORNS.............................................................................. 20FIGURE 2-8: POLARIZATION AND ELEVATION ANGLE VERSUS LATITUDE AND LONGITUDE

............................................................................................................................................................. 21FIGURE 2-9: C BAND FREQUENCY/POLARIZATION PLAN.............................................................. 22

FIGURE 2-10 -U.S. DOMESTIC C-BAND GEOSYNCHRONOUS SATELLITES ................................. 23FIGURE 2-11: - U.S. DOMESTIC KU BAND SATELLITESAND LOCATION ................................... 24FIGURE 2-12 GENERAL ARRANGEMENT OF THE DUAL SPIN SPACECRAFT.............................. 26FIGURE 2-13 SPACECRAFT ORBITAL ASSIGNMENT BOX ........................................................... 27FIGURE 2-14: THREE AXIS OR BODY STABILIZED SPACECRAFT................................................. 28FIGURE 2-15: GEOMETRY OF ORBITAL INCLINATION.................................................................... 29FIGURE 2-16: REPRESENTATIVE DAILY SATELLITE PATH OF AN INCLINED ORBIT

SATELLITE ........................................................................................................................................ 30FIGURE 2-17: SIMPLIFIED BLOCK DIAGRAM OF COMMUNICATIONS PAYLOAD..................... 31FIGURE 2-18 TYPICAL WIDEBAND SATELLITE COMMUNICATIONS RECEIVER....................... 32FIGURE 2-19 INTERMODULATION EFFECTS. ..................................................................................... 33FIGURE 2-20: INTERMODULATION EFFECTS FROM MULTIPLE CARRIERS................................ 34FIGURE 2-21 TYPICAL INPUT/OUTPUT AMPLIFIER CHARACTERISTIC....................................... 35

FIGURE 2-22 GENERATION OF A SHAPED BEAM ANTENNA PATTERN USING MULTIPLEFEED HORNS AND AN ASSOCIATED FEED NETWORK........................................................... 37FIGURE 2-23 SPACECRAFT ANTENNA BEAM SHAPING COVERAGE OF MEXICO..................... 37FIGURE 2-24 POWER FLUX DENSITY. .................................................................................................. 39FIGURE 2-25 GALAXY IV TRANSPONDER 23 G/T (DBK).................................................................. 40FIGURE 2-26 EIRP FOOTPRINT............................................................................................................... 43FIGURE 2-27 MAJOR CONTRIBUTORS TO ANTENNA NOISE IN THE SATELLITE RECEIVER. . 46FIGURE 2-28: BLOCK DIAGRAM SHOWING SATELLITE RECEIVER NOISE CONTRIBUTIONS.

............................................................................................................................................................. 47FIGURE 2-29: CHARACTERISTICS OF DIFFERENT METHODS OF SATELLITE ACCESS ............ 49FIGURE 2-30: TYPICAL FDM TRANSPONDER ACCESS..................................................................... 49FIGURE 2-31: SPREADING A SIGNAL TO PERMIT CDMA OPERATION ......................................... 50FIGURE 2-32: SPECTRUM OF A SIGNAL BEFORE AND AFTER SPREADING FOR CDMA .......... 51FIGURE 2-33: ONE WAY, POINT TO MULTIPOINT LINKS................................................................. 52FIGURE 2-34: MESH NETWORK ............................................................................................................. 53FIGURE 2-35: STAR NETWORK TOPOLOGY........................................................................................ 54FIGURE 2-36 POWER LEVEL DIAGRAM- UPLINK.............................................................................. 56FIGURE 2-37: ANTENNA SIDELOBE DISCRIMINATION.................................................................... 58FIGURE 2-38 UPLINK INTERFERENCE. ................................................................................................ 59FIGURE 2-41: PATH LOSS BETWEEN SYNCHRONOUS ORBIT AND SUB-SATELLITE POINT . .. 65FIGURE 2-42 FREE SPACE LOSS VERSUS GROUND STATION ELEVATION ANGLE. ................. 66FIGURE 2-43 DOWNLINK INTERFERENCE. ......................................................................................... 67


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FIGURE 2-44 AMPLIFIER INPUT OUTPUT CHARACTERISTIC SHOWING THEORETICAL THIRD

ORDER DISTORTION AND 2 TONES. ........................................................................................... 68FIGURE 2-46: EXAMPLE OF ACCURACY FROM TWO LINES OF POSITION.................................. 70FIGURE 2-47: TYPICAL TDOA MEASUREMENT SETUP.................................................................... 71FIGURE 2-48 CAUSE-EFFECT DIAGRAM SHOWING VARIOUS INTERFERENCE SOURCES...... 72FIGURE 2-49 RAIN ATTENUATION VS. NOISE TEMPERATURE...................................................... 74

FIGURE 2-50: RAIN ZONE MAPS IN THE US (CRANE MODEL)........................................................ 75FIGURE 2-51: SPOT BEAM CONFIGURATIONS................................................................................... 80FIGURE 2-52: TECHNICAL DIFFERENCES BETWEEN C, KU AND KA BAND SATCOM.............. 81FIGURE 2-53 MERITS OF C, KU - AND KA-BAND FOR SATELLITE COMMUNICATIONS........... 82FIGURE 2-54 EFFECT OF MODULATION INDEX ON FREQUENCY MODULATION SPECTRUM88FIGURE 2-55: RELATIONSHIP OF C/N TO SNR IN AN FM CARRIER............................................... 88FIGURE 2-56: NTSC FM MODULATED CARRIER AND SIGNAL TO NOISE RATIO....................... 89FIGURE 2-57: PHASE RELATIONSHIPS IN SIGNALS.......................................................................... 96FIGURE 2-59: SIMPLIFIED BLOCK DIAGRAM, TIME DOMAIN OF BIPHASE MODULATOR. ..... 98FIGURE 2-60 SIMPLIFIED BLOCK DIAGRAM, BIPHASE DEMODULATOR................................... 99FIGURE 2-61 SIMPLIFIED BLOCK DIAGRAM, QPSK MODULATOR SHOWING (GRAY CODED)

PHASE STATES. .............................................................................................................................. 100FIGURE 2-62 MODULATOR DATA STREAMS FOR QPSK AND OKQPSK. .................................... 101FIGURE 2-63 RF ENVELOPE FOR QPSK AND OKQPSK SIGNALS................................................. 102FIGURE 2-64 PLOT OF THEORETICAL EB/NO VS. BER. .................................................................. 104FIGURE 2-65: 8 PSK CHARACTERISTICS............................................................................................ 104FIGURE 2-66: 16-QAM CONSTELLATIONS......................................................................................... 105FIGURE 2-67: ERROR RATES OF PSK MODULATION SYSTEM. .................................................... 106FIGURE 2-68: COHERENT ORTHOGONAL FREQUENCY DIVISION MULTIPLEX MODULATION

........................................................................................................................................................... 107FIGURE 2-69: BLOCK ENCODER.......................................................................................................... 108FIGURE 2-70: BLOCK DECODER.......................................................................................................... 108FIGURE 2-71: LDPC PERFORMANCE COMPARISON........................................................................ 109FIGURE 2-72 COMPUTATIONAL BASIS OF LDPC............................................................................. 109FIGURE 2-73: CONVOLUTIONAL ENCODER ..................................................................................... 110FIGURE 2-74: VITERBI DECODING OF CONVOLUTIONAL CODING............................................ 110FIGURE 2-75: MODEM PERFORMANCE WITH AND WITHOUT FEC............................................. 111

FIGURE 2-76: CONCATENATED CODING........................................................................................... 112FIGURE 2-77: CONCEPT OF INTERLEAVING..................................................................................... 112FIGURE 2-78: DISPERSAL OF ERRORS IN AN INTERLEAVER ....................................................... 113FIGURE 2-79 NTSC COUNTRIES........................................................................................................... 114FIGURE 2-80: SECAM COUNTRIES ...................................................................................................... 115FIGURE 2-81 NTSC SIGNAL................................................................................................................... 115FIGURE 2-82: NTSC WAVEFORM......................................................................................................... 116FIGURE 2-83: TYPES OF VIDEO............................................................................................................ 117FIGURE 2-84 OVERVIEW OF THE A TO D CONVERSION PROCESS ............................................. 119FIGURE 2-85: VIDEO SAMPLING FREQUENCIES AND BIT RATES............................................... 120FIGURE 2-86 SAMPLING POINTS (FS= 4F SC) ..................................................................................... 120FIGURE 2-86: COMPOSITE QUANTIZING LEVELS........................................................................... 121FIGURE 2-87: 8 BIT BINARY CODES.................................................................................................... 122

123FIGURE 2-88 BINARY WORDS FOR BURST SAMPLES .................................................................... 123FIGURE 2-89: UNCOMPRESSED VIDEO DATA RATES .................................................................... 124FIGURE 2-90: MOTION COMPENSATION IN MPEG 2 ....................................................................... 125FIGURE 2-91 ENCODING PROCESS SIMPLIFIED .............................................................................. 126FIGURE 2-92: BASIC ELEMENTS IN MPEG 2 ENCODER.................................................................. 129FIGURE 2-93 MPEG TRANSPORT PACKET STREAM........................................................................ 130FIGURE 2-94 MPEG TRANSPORT STREAM PACKET........................................................................ 130


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FIGURE 2-95 MPEG TRANSPORT STREAM PACKET MULTIPLEXING......................................... 131FIGURE 2-96 PACKET DEMULTIPLEXING......................................................................................... 132FIGURE 2-97 BASIC ELEMENTS OF THE MPEG-2 DECODER......................................................... 132FIGURE 2-98: COMPLETE DIGITAL SYSTEM .................................................................................... 133FIGURE 2-99 MPEG-2 LEVELS AND PROFILES................................................................................. 135FIGURE 2-100 MPEG 4-10 ENCODING PROCESS............................................................................... 138

FIGURE 2-101: JPEG 2000 PROCESS..................................................................................................... 139FIGURE 2-102 HDTV STANDARDS AND IMPLEMENTATION ........................................................ 140FIGURE 2-103 : ATSC DIGITAL TELEVISION LAYERS .................................................................... 141FIGURE 2-104: FOUR CURRENTLY DEFINED ATSC HDTV FORMATS......................................... 142FIGURE 2-105 COMPRESSED VIDEO LINK BUDGET (OUTPUTS IN ITALICS) ............................ 144FIGURE 2-106: DIFFERENCE BETWEEN KU FSS AND BSS ............................................................. 145FIGURE 2-107 COMPARISON OF DBS SYSTEMS............................................................................... 145FIGURE 2-108 REPRESENTATIVE DIRECTV SPOT BEAM COVERAGE........................................ 146

FIGURE 3-1 COMPOSITE SATELLITE EARTH STATION.................................................................. 147FIGURE 3-2 LARGE KU BAND EARTH STATION.............................................................................. 148FIGURE 3-3 BASIC ELEMENTS OF AN ANALOG TV EXCITER...................................................... 150FIGURE 3-4 DUAL CONVERSION PROCESS ................................................................................... 151FIGURE 3-5 SUBCARRIER ATIS-BLOCK DIAGRAM......................................................................... 152FIGURE 3-6 DIGITAL EXCITER ............................................................................................................ 153FIGURE 3-7 SIMPLIFIED BLOCK DIAGRAM OF DIGITAL SCPC UPLINK..................................... 153FIGURE 3-8 TWO OR MORE SCPC CHANNELS FEEDING A COMMON UPCONVERTER .......... 154FIGURE 3-9 CHARACTERISTICS OF DIFFERENT POWER AMPLIFIERS....................................... 155FIGURE 3-10 SHARING AN UPLINK WITH MORE THAN ONE ANTENNA. .................................. 157FIGURE 3-11 SIX CHANNEL FILTER DIPLEXER MULTIPLEXER................................................... 158FIGURE 3-12 SIX CHANNEL HYBRID MULTIPLEXER..................................................................... 158FIGURE 3-13 TWELVE CHANNEL MULTIPLEXER USES FILTERS AND HYBRID ...................... 159FIGURE 3-14 MONITOR AND NON RADIATION TEST APPARATUS............................................ 160FIGURE 3-15 GENERAL CONFIGURATION OF LNAS, LNBS AND LNCS.................................. 161FIGURE 3-16: L BAND TO C AND KU CONVERSION CHART......................................................... 162FIGURE 3-17 EXAMPLE WHERE POST AMPLIFIER IS REQUIRED TO BOOST LEVELS AND

DECREASE NOISE.......................................................................................................................... 163FIGURE 3-18: INTEGRATED RECEIVER-DECODER.......................................................................... 164FIGURE 3-19 PRIME FOCUS AND DUAL REFLECTOR GEOMETRY.............................................. 147FIGURE 3-20 OFFSET FED ANTENNA GEOMETRY .......................................................................... 167FIGURE 3-21: VIDEO RECEIVE ONLY EARTH STATION................................................................. 170

FIGURE 4.1 CAUSES OF INTERFERENCE (SOURCE: SUIRG).......................................................... 175


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CHAPTER 1: INTRODUCTION

This document is intended primarily as a textbook for the training of earth station

operators who have responsibility for accessing satellites (uplinks). The primary thrustis directed toward operations with U.S. Domestic satellites. However, the operator mustbe constantly aware of the fact that he (or she) is a part of a worldwidetelecommunications infrastructure. Improper operation of an uplink earth station canadversely affect: 1) the network of which the earth station is a part, 2) other networks inthe same satellite, 3) other U.S. domestic satellites, 4) other foreign or regional satellitesand 5) international telecommunications traffic.

There can be severe economic consequences due to improper earth station operations.The importance to the network in which the earth station is a part will vary with thecircumstances. Each operator should be aware of this and act in accordance with the

interests of his (or her) employer or client. Furthermore, interference to other systemscan result in criminal prosecution with both fines and/or jail sentences depending onthe circumstances. Repeated cases of unintentional or negligent interference can resultin fines and/or loss of the FCC license for the earth station.

This text includes a short history of communication satellites in the U.S. and a discussionof the regulatory aspects of U.S. domestic and other satellite systems in this section.Section 2 deals with BASIC CONCEPTS including: a) satellite specifics (orbit/orbitcontrol, communication subsystem, frequency/polarization plans and importantparameters), b) directional antennas, c) noise and d) link budgets for various commonlyused modulation techniques. Section 3 deals with GROUND EQUIPMENT, and section

4 covers UPLINK OPERATIONS.


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BRIEF HISTORY OF COMMUNICATION SATELLITES IN U.S.

The U.S. department of Defense and NASA initiated a number of projects in the late1950s and early 1960s directed toward satellite communications. The first operational

commercial communications satellite was Early Bird launched in 1965 for Intelsatfollowed by Intelsat II in 1966. In 1970, the U.S. government announced an open skiespolicy whereby an entity with the legal, technical and financial capabilities could launchand operate satellites serving the U.S. domestically. The first U.S. domestic satellite tobe launched was Westar I (1974).The orbital arc is administered on a global basis by the InternationalTelecommunications Union (ITU), which is an agency of the United Nations (UN). TheFCC administers and regulates the Geostationary Orbit for commercial use in the U.S.Domestic Satellite Service. The FCC has authorized satellites to operate in theGeostationary Orbital Arc between 62west longitude to 146west longitude for U.S.Domestic Service.


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Copyright 2006 3 A

Figure 1-1 Worldwide Satellite Coordination

UNITED NATIONSINTERNATIONAL

TELECOMMUNICATIONS UNION

REGION 1EASTERNEUROPE

REGION 1WESTERNEUROPE

REGION 1AFRICA

REGION 2THE AMERICAS

NORTH/CENTRALAMERICA

SOAME

UNITEDSTATES

CANADAMEXICO

UNITEDSTATES

143 121 105


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As shown in Figure 1-1, Coordination of all satellites is done by a branch of theInternational Telecommunications Union (ITU), which in turn is a part of the UnitedNations (UN). The U.S. Department of State is the official U.S. member of ITU, and theFCC provides support. An application for a space station must be submitted to the FCC

in accordance with the FCC rules. The FCC then forwards the pertinent information tothe ITU, which then coordinates with other entities for any potential conflict orinterference potential.Three classes of satellite services have been established in the U.S. They are: a) FixedSatellite Service (FSS), b) Broadcast Satellite Service (BSS) and c) Mobile Satellite Service(MSS). All three classes are administered by the International Bureau of the FCC, asshown in Figure 1-2. In South and Central America rules are established by CITEL, theInter-American Telecommunications Commission.

This course of study will emphasize the FSS. The rules dealing with the FSS are given inthe "Code of Federal Regulations 47 Part 25". An uplink operator should be familiar withthese rules and maintain the latest published version at the earth station. For uplinkstations that operate in the Broadcast Satellite Service (BSS), the rules are given in Codeof Federal Regulations 47, Part 100.


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Figure 1-2: U.S. Domestic Service

FCC

INTERNATIONAL

BUREAU

MOBILESATELLITE

SERVICE

FIXEDSATELLITE

SERVICE

-2 degree spacing-linearpolarization,-C, Ku, Ka Band-assignments byorbital arc location

-9- cpo---ach

fr

-4 degree spacing- circular polarization--L, S, C and Ku Band-assignments bychannel or frequency


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There are three frequency bands currently used in the FSS in the United States. They areC Band (5925 to 6425 MHz up, 3700 to 4200 MHz downcommonly called 6/4 GHz), Kuband (14000 to 14500 MHz up, 11700 to 12200 MHz downcommonly called 14/12 GHzand Ka Band, (28,350 to 28600 and 29,250 to 30,000 uplink and 18300 to 18,800 and 19,700to 20.200 downlink) commonly called 20/30 GHz. Full details are given later in this text.A chart of all frequency bands is given in Figure 1-3.

During classroom sessions, the various characteristics, advantages and disadvantages ofthe various frequency bands will be discussed. Differentiators include beam sizesavailable, sharing of the band with other services, and antenna sizes required, as well asthe relative amount of atmospheric attenuation that affects the signal as it passesthrough the earths atmosphere. As shown in Figure 1-4, this attenuation differssignificantly for the three FSS frequency bands of interest.

FREQUENCY (MHz)DESIGNATION Ref. Data for RadioEngineers

US Navy RSGB

I 100 - 150

G 150 - 225

P 225 - 390 225 - 390

L 390 - 1,550 390 - 1,550 1,000 - 2,000

S 1,550 - 5,200 1,550 - 3,900 2,000 - 4,000

C 3,900 - 6,200 3,900 - 6,200 4,000 - 8,000

X 5,200 - 10,900 6,200 - 10,900 8,000 - 12,000

Ku15,350 -17,250

15,250 -17,250

12,000 -18,000

K

Ka

10,900 -36,000

33,000 -36,000

10,900 -36,000

33,000 -36,000

18,000 -26,500

26,500 -40,000

Q 36,000 - 46,000 36,000 - 46,000 33,000 - 50,000

U 40,000 - 60,000

V 46,000 - 56,000 46,000 - 56,000

W 56,000 - 100,000 56,000 - 100,000

Figure 1-3: Frequency Band Nomenclature


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Different authors use different nomenclature for frequency bands. The chart aboveshows three- a standard engineering text, the US Navy and the Radio Society of GreatBritain.

International ServiceThere are satellites other than U.S. domestic ones within the field of view of earthstations located in the U.S. These include satellites serving other countries in North andSouth America, as well as international satellites located above the Atlantic and PacificOceans. Of particular concern are satellites serving the northern hemisphere. They arementioned here because faulty operation of earth stations in the U.S. domestic servicecan cause interference to these satellites.

The U.S. has formal arrangements with Canada and Mexico regarding assignments ofsatellites. South American satellites will be interspersed with North American satellites.Future discussion in this text dealing with the geostationary orbital arc and directional

antennas will indicate why reasonably large antennas are required in uplinking. TheSouth American Satellites are, or will be, located as little as one degree or less from U.S.Domestic satellites.

Figure 1-4: Atmospheric Attenuation at Different Frequency Bands

0.004

0.01

0.1

1

3 10 60

ATTENUATIO

N

(dB/km)

H2O

O2

0.02

0.05

0.2

0.5

C-BAND

Ku-BAND Ka-BAND

FREQUENCY (GHz)

3020


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CHAPTER 2: BASIC CONCEPTS

In order to properly operate a satellite uplink earth station, an understanding of theoverall infrastructure in which the station is a part is necessary. There are no mysteries

here. A satellite is sometimes referred to as a bent pipe in space, and the popularpress almost always refers to a satellite transmission as a signal bounced off of asatellite 22,300 miles away. In fact, most, but not all present day satellites can be calledMicrowave Heterodyne Repeaters and a satellite link can usually be characterized as atwo-hop microwave system. Of course, the paths are rather long as compared toterrestrial links and the repeater tower is rather tall.

Decibel Notation

Decibel notation is used extensively in this course and in satellite communications,

normally when dealing with power and bandwidth. Decibels were invented byengineers as a tool to easily multiply large and small numbers without the need forcalculators, computers and slide rules. A tutorial on decibels is given in Appendix B ofthis text. However, decibels are easy to use when certain principals are understood anda few reference numbers are able to be referred to. Figure 2-0 provides a quick referencelist of decibels and their corresponding linear (normal) power or bandwidth values.

Linear- (Multiply) dB- (Add)

1 0 dB

1.26 1 dB

2 3.0 dB

3 4.8 dB

4 6.0 dB

5 7.0 dB

7 8.5 dB

10 10 dB

20 13 dB

30 14.8 dB

40 16 dB

50 17 dB

70 18.5 dB100 20 dB

200 23 dB

1000 30 dB

10,000 40 dB

Figure 2-0 Quick Reference list of Decibels


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Copyright 2006 10 All rights reservedSkjei Telecom, Inc.

Directional Antennas

Before proceeding with specifics of satellites and satellite links, an initial discussion ofdirectional antennas is warranted, since orderly use of satellites is dependent on antenna

characteristics. Antennas will discussed further in other sections of the text, but at thispoint a few basics should be understood.

Antenna Gain

The question most frequently asked about antennas is, How can a passive device, likean antenna, have gain? The answer is that antenna gain is a measure of how well theantenna concentrates its radiated power in a given direction. Gain is the ratio of thepower radiated in a given direction to the power radiated in the same direction by astandard antenna (usually an isotropic radiator). An isotropic radiator is one where theradiated power is the same in all directions (point source).

The gain of an antenna can be related to the effective area (Ar) of its aperture by theformula:

G= 24

rA

Where: is wavelength, and

Ar =

Where: is the efficiency, and

A is the actual area of the aperture.

In most satellite earth station applications, a paraboloidal surface is used as the mainreflecting surface. Typical values of efficiency in the direction of maximum radiation are50 to 70 percent, depending on design.

It is instantly obvious that the larger the antenna the higher the (on-axis) gain, assumingthat the efficiency is the same. Antenna gain specifications from manufacturers implymaximum (on-axis) radiation relative to an isotropic radiator.


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Problem: What is the on-axis gain of a 10 meter diameter antenna operating at6.0 GHz, whose efficiency is 65%?

Solution: metersx

x05.0

100.6

1039

8

==

4

22 Dr

==

G =( )

( )5

2

2

2

10.5661.205.4

1065.04=

x

xx

Gain (in decibels) = 54.1 dB

Radiation Pattern

In a practical antenna, not all of the available power is radiated in (or received) from justone direction. Energy is lost in: 1) feed losses, 2) spillover from feed to reflector(s), 3)forming the main beam, and 4) sidelobes. A typical radiation pattern is shown in Figure2-1. The shape of the main beam and sidelobe levels is a function of the intrinsic designand mechanical imperfections in the reflecting surface(s).

Figure 2-1 shows what is commonly called the co-pol or co-polarization pattern. Thecross polarization pattern is also important and will be discussed later.

Further discussion on antennas is contained in Chapter 3. In that section, practicalconsideration of antenna performance and maintenance are considered.


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Figure 2.1 Illumination of a Parabolic Reflector

Geostationary Orbit

The earth rotates about its N-S axis at the rate of one revolution per day (24 hours). Themoon, which is an earth satellite, rotates about that axis at a rate of about one revolutionper month. Low altitude earth satellites such as an orbiting space shuttle operating at analtitude of 150 miles, has a rotational rate of about 90 minutes. An object placed on aline 22,300 statute miles above the earths equator will have a rotational rate that isexactly the same as the earths rotational rate. This is the well known GeostationaryOrbit, and has the unique property of being fixed in space relative to all points on theearth. Figure 2-2 shows this unique orbit.


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Figure 2-2 Geostationary Satellites

The advantage of this orbit is obvious. Expensive earth station antenna tracking is notrequired as long as the satellite is kept within the beam of the earth station antenna.Domestic satellites are required to maintain their assigned orbital position within 0.05 .This puts a practical limit at C Band of about 35 feet diameter (for 0.5 dB loss) on earthstation dish size for no tracking function.

Satellite Launch Sequence

As shown in Figure 2-3 below, a satellite launched into geosynchronous orbit is firstlaunched into a circular orbit (a) which circles the earth. It then is placed into anelliptical transfer orbit (b) by firing a rocket or expending fuel at the transfer orbitsperigee.After several rotations of the earth in the transfer orbit, an apogee kick motor or otherpropellant is fired at the apogee, and the satellite is placed into geosynchronous orbit.


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Figure 2-3: Satellite Launch Sequence

Satellite Visibility from Earth

As indicated above, the FCC has authorized U.S. Domestic satellites in the orbital arcfrom 62to 146west longitude. Assuming there are no local obstacles (buildings,mountains, etc.) line of sight can be maintained from all points in the contiguous 48states, continental U.S. (CONUS), with greater than 5elevation angle of the earthstation antenna. Less than 5is generally undesirable at C Band and less than 10elevation angle is not desirable at KuBand.

Formulas for calculating the pointing angles of earth station antennas in the northernhemisphere to satellites in the geostationary arc are as follows:


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True Azimuth, AZ = 180+ arc tan

sin

tan

Where: is the earth station latitude, andis the relative longitude of theearth station with respect to the satellite longitude. (Satellite longitude minus the

earth station longitude).

True Elevation (with respect to earth),

EL = - arc tan

AZ

DR

sin/sin

/coscos

where: R is radius of earth (3,957 miles), and

D is radius of the satellite orbit (26,244 miles).

It should be noted that when attempting to point the antenna, if a compass is used

for azimuth, magnetic declination must be taken into account. Figure 2-4 refers.

Figure 2-4: North American Magnetic Declination


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Figure 2-5 is a plot of the azimuth and elevation formulas on the previous page.

Figure 2-5 Ground Antenna Elevation and Azimuth for Stationary Satellites

Example: Earth Station location: Los Angeles

34 0330 N. Latitude

118 0740 W. Longitude

Satellite: SPACENET II @ 69 W. Longitude


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Solution: Station Latitude = a = 34.06

Station Longitude = 118.13

= 69 118.13 = -49.13

tan = - 1.155

sin a = 0.560

cos = 0.654

sin = -0.756

cos a = 0.828

R/D = 0.15077

13.64180560.0

155.1tan180 =

+= arcAZ

AZ= 115.86

sinAZ= 0.8998

8998.0/756.0

15077.828.0654.0arctan

=

xEL

EL= - arc tan (-.465)

EL= 24.94

Sun Outages

As indicated above, geostationary satellites are in an orbital arc above the equator,which means they are in the equatorial plane. During the spring (vernal) and fall


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(autumnal) Equinox, the sun also passes through the equatorial plane (definition ofEquinox).

As seen from the ground, the sun seems to pass behind a satellite once a day. Duringthe time when both the satellite and sun are in the earth station antenna field of view,

the RF energy from the sun can overpower the signal from the satellite. It is this loss ordegradation of signal that is referred to as Sun Outage.

Figure 2-6: Geometry of Sun Outage.

The severity and duration of a sun outage depends on many factors, and will not bedealt with here. However, the date and time of maximum effect is predictable. Forpractical antennas and for practical satellite signal strengths, an outage will usuallyoccur for 3 or 4 days in each Equinox for a period of 1 to 5 minutes. Satellite operatorscan assist any user with specific information.

There are commercially available programs that can also provide predictions.

A simplified formula for the outage angle shown in Figure 2-6 is:

Outage angle = 3 dB Beamwidth + apparent radius of sun = 11/F/D + 2.5

Where: F is downlink frequency in GHz

D is diameter of antenna in meters.

For a 5 meter antenna at 4 GHz, the outage angle is approximately 3.


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Angular Distance Between Satellites

It should be noted that in the FSS service, orbital slots whether assigned or not call for auniform 2 spacing between Kuband satellites (12/14 GHz), and C Band satellites (4/6

GHz). This 2 spacing policy has been in effect since 1983.

From an uplink standpoint, it is obvious that to preclude interference to adjacentsatellites, a large antenna (narrow beam) and low sidelobes are required.

In future sections of this text, interference considerations are quantified. However,paramount to an uplink operator should be the understanding that his (or her)antenna should be pointed accurately and should meet the FCC standard forsidelobes.

Frequency/Polarization Plan

U.S. DomesticDetails of the satellite communications subsystem (payload) are given in section 2.4below. However, before describing the spacecraft subsystems, it is worthwhile todiscuss the channels of communications of which the satellites are a part.

Transponders and Frequencies

In the context of this section, a channel of communication and the term, transponderare used interchangeably. In spacecraft terms, as we shall see later, a transponder is achannel of communication. A transponder is characterized as having: 1) a centerfrequency, 2) a usable bandwidth, 3) certain uplink sensitivity and saturationcharacteristics, 4) certain power output characteristics and 5) coverage (footprint) for

characteristics 3 and 4. We will also see in later sections, that a transponder can supportmore than one channel of communication because of its relatively wide bandwidth. Insome cases, multiple channels are modulated on a single carrier. In other cases, a singlechannel is modulated on a carrier, and a multiplicity of carriers is transmitted through atransponder.

The FCC has set aside 500 MHz of bandwidth for uplinking and downlinking to boththe C band and Kuband for the U.S. Domestic FSS Service. The rules do not dictate howthis bandwidth is to be utilized. The uplink frequency range at C Band is 5,925 to 6,425MHz, and the C Band downlink is 3,700 to 4,200 MHz. Elsewhere in the world,extended C Band is starting to be used, but it has not been assigned in the US at this

time. At KuBand, the uplink frequency range is 14,000 to 14,500 MHz, and the downlinkis 11,700 to 12, 200 MHz. Similarly, elsewhere in the world, extended Ku band has beenassigned but it has not been assigned by the FCC for US use.The FCC has also set aside assignments for Ka band as discussed in section 1 and thesesatellites are just now starting to be placed into service.


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Polarization

Electromagnetic waves and antennas are alwayspolarizedin some manner. Thepolarization may be linear or (approximately) circular. Linear polarizations and circularpolarizations are aligned in space as shown in Figure 2-7. Most domestic FSS satellites

are linearly polarized. A linearly polarized antenna receives maximum power from anincident linearly polarized wave if the tilt anglesof the wave and the antennapolarizations are aligned similarly in space). The wave is then said to be co-polarized. Asthe tilt angle of the wave or antenna rotates from co-polarization, the received powerdecreases. When the tilt angles are 90apart as shown in Figure 2-7, the antenna is crosspolarizedto the wave and receives no power from it. The antenna and the wave thenhave orthogonalpolarizations. A given satellite can employ two orthogonal polarizationsthat exist simultaneously and carry different information without interference. Thisprinciple,frequency reuse, is used to increase the information capacity of satellites andof the geosynchronous orbit.Early satellites (Westar 1, 2, 3, and SBS 1, 2, 3, 4) utilized a single polarization for

transmission. Modern satellites utilize orthogonal linear polarization, and therefore arecapable of more channels of communication through frequency reuse. One of the mostcommon errors made in uplink transmission is to transmit on the wrong polarization.Even more common is to have a slightly misadjusted antenna polarization or a defectiveantenna with poor polarization isolation. Erroneous polarization or poor polarizationisolation in the uplink antenna can cause harmful interference to adjacent channels onopposite polarization, or to adjacent satellites on the same channel but oppositepolarization.

Figure 2-7: Linear Polarization of Radiation from Vertically and HorizontallyPolarized Feed Horns


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The terms vertical and horizontal polarizations apply to linear orthogonal polarizationsof the satellite antenna at the sub-satellite longitude. The polarization angle of anantenna transmitting to or receiving from a satellite will depend on the earth stationlocation. Figure 2-8 shows polarization angle and elevation angle for latitude andlongitude of the earth station. This figure should be used as an approximation only.

Final adjustment should be made by coordination with the satellite operator.

Figure 2-8: Polarization and Elevation angle Versus Latitude and Longitude


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For completeness, some satellites not in the domestic FSS arc also used a type ofpolarization known as circular polarization. Intelsat uses this at C band for historicalreasons and MSS and BSS (Broadcast Satellites) use this at Ku band to simplify antennainstallation for DBS dishes. In circular polarization, the antenna polarity does not needto be specifically aligned relative to the satellite.

C Band

A de-facto standard frequency plan has evolved at C band. The FCC places U.S.domestic satellites so that adjacent satellites are of opposite polarization. Figure 2-9below is a frequency polarization plan that reflects the current situation at C band.

CENTERFREQUENCY

POLARIZATION

PLAN A

POLARIZATION

PLAN B

UPLINK DOWNLINK NO. UP DN NO. UP DN5945 3720 1 H V 1 V H

5965 3740 2 V H 2 H V5985 3760 3 H V 3 V H6005 3780 4 V H 4 H V6025 3800 5 H V 5 V H6045 3820 6 V H 6 H V6065 3840 7 H V 7 V H6085 3860 8 V H 8 H V6105 3880 9 H V 9 V H6125 3900 10 V H 10 H V6145 3920 11 H V 11 V H6165 3940 12 V H 12 H V6185 3960 13 H V 13 V H6205 3980 14 V H 14 H V6225 4000 15 H V 15 V H6245 4020 16 V H 16 H V6265 4040 17 H V 17 V H6285 4060 18 V H 18 H V6305 4080 19 H V 19 V H6325 4100 20 V H 20 H V6345 4120 21 H V 21 V H6365 4140 22 V H 22 H V6385 4160 23 H V 23 V H

6405 4180 24 V H 24 H VFigure 2-9: C Band Frequency/Polarization Plan

Figure 2-10 below shows current active C band satellites, their orbital location and thetransponder/polarization plan.


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Satellite West Longitude Polarization Plan

AMC 8 139 A

AMC 7 137 B

AMC 10 135 A

GALAXY 1R 133 B

AMC 11 131 A

INTELSAT AMERICA 7 129 B

GALAXY 13/HORIZONS1 127 A

GALAXY 12 125 B

GALAXY 10R 123 A

INTELSAT AMERICA 13 121 B

ANIK E2 119 A

SATMEX 5 117 B

SOLIDARIDAD 2 113

ANIK F1 107 B

AMC-2 105 A

AMC 1 103 B

AMC 4 101 A

GALAXY 4R 99 B

INTELSAT AMERICA 5 97 A

GALAXY 3C 95 B

INTELSAT AMERICA 6 93 A

GALAXY 11 91 B

AMC 3 87 B

AMC 9 85 A

AMC 6 72 A

Figure 2-10 -U.S. Domestic C-Band Geosynchronous Satellites

Ku Band

At Ku Band there is no current standard (de-facto or mandated) for the operationalsatellites frequency and polarization plans. A trend appears to be forming similar to theDe-Facto C Band plan whereby most modern satellites have 24, 36 MHz transponderswith 40 MHz spacing of center frequency on each polarization. The net effect of this


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non-standardization is that unless careful coordination is done, polarization isolationcannot be counted on in any link involving interference to or from other satellites in theorbital arc. The co-polarized sidelobe response of the ground antenna is the only toolavailable to the transmitting or receiving earth station to avoid interference.

Satellite West Longitude

INTELSAT AMERICA 7 129

GALAXY 13/HORIZONS I 127

GALAXY 10R 123


ANIK E2 118

SATMEX 5 117

SOLIDARIDAD 2 113

ANIK F2 111

ANIK F1 107

AMC 2 105

AMC 1 103

AMC 4 101

GALAXY 4R 99


GALAXY 3C 95

INTELSAT AMERICA 6 93GALAXY 11 91

AMC 3 87

AMC 9 85

AMC 5 79

SBS 6 74

AMC 6 72

ESTRELA DO SUL 63

Figure 2-11: - U.S. Domestic Ku Band Satellitesand Location

The Communication Satellite

There are two main hardware sections that comprise a communications satellite. Theyare the communications payload containing the actual radio communications equipment


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for receiving and transmitting signals, and the spacecraft bus which provides thesupporting vehicle to house and operate the payload. Each major section consists ofsubsystems, which contribute to the efficient functioning of the satellite. Only thefundamentals are given here and mainly as they apply to the necessary skill andknowledge of an uplink operator. For a more complete description, the interested

student is urged to read references 1 and 2. Reference 1 is an excellent treatmentwithout mathematical encumbrance. Reference 2 delves more deeply into themathematics and physics involved in orbital dynamics, and is directed to theengineering professional in the field.

Spacecraft Bus

A satellite has a directive antenna on board as part of the communications payload. Thesatellite antenna pointing and/or attitude control systems affect earth stations accessingit. It is worthwhile therefore, to know and understand some of the imperfections in thatorbit.

The treatment here is general in nature; therefore, the operator is urged to obtain specificinformation on the satellite he (or she) is working with. This information can generallybe obtained from the satellite operator/owner.

Stabilization and Station Keeping

There are two types of stabilization in present day satellites. They are: 1) spinstabilization and 2) body (three axis) stabilization. Modern satellites are body stabilizedto support a more powerful satellite.

Figure 2-12 depicts the elements of a simple spinner. The simple spinner produces avery stable and reliable design. However, it has limited communications capability.The spinner is unconditionally stable, meaning that the spacecraft will stay erect andeven correct itself if disturbed by an external force. In the design and construction of thesimple spinner, the body and major components are arranged to provide maximumrotational inertia about the spin axis. This produces a drum shape more akin to that of atuna can than to that of a pencil.

Geosynchronous satellites are assigned specific longitudinal positions above theequator. To reduce adjacent satellite interference, satellite stations or "boxes" are definedat these positions in the east-west and north-south directions, as shown in Figure 2-13.

A satellites box size is assigned based upon its operational frequency band and isdefined as assigned longitude +0.05 and 0 latitude + 0.05 (box size of 0.10 in the E-W/N-S directions); approximately 45 miles on a side.


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Figure 2-12 General Arrangement of the Dual Spin Spacecraft.

It is normal for satellites to move within their box due to gravitational and other effectsassociated with the Earth, sun, and moon. Normally, the satellite operator will allow thespacecraft to drift from one end of the box to the far end before utilizing thespacecrafts onboard stationkeeping (normally hydrazine) fuel to position it at theopposite end of the box. For this reason, it is important that ground station antennas bealigned when the satellite is passing through box center for peak performance,particularly for large, non-tracking antennas. This information can usually be obtainedfrom the spacecraft operator, normally on his web site.

It should be noted that the entire communications payload is despun. This allows greatflexibility in the antenna beam forming through a multiplicity of antenna feeds. It alsoallows a larger payload. Dynamic stability is much more complex in the dual spinnerand the interested student can gain insight in references 1 and 2. Antenna pointing inspinning satellites is usually provided by use of a ground beacon and tracking system.

Earth and sun sensors can augment the ground beacon.


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Figure 2-13 Spacecraft Orbital Assignment Box

Body stabilized satellites utilize high speed gyroscopes or momentum wheels to providestiffness in three directions and act as an inertial reference. Figure 2-14 shows thegeneral arrangement. Antennas are usually mounted on the earth facing side, and

antenna pointing is augmented by sun and earth sensors.

Power

Power to operate a communications satellite is derived from solar cells and a storagebattery, which is necessary during periods when the satellite is in eclipse (the period inwhich the solar cells are not able to provide power because the satellite is in the earthsshadow). Modern satellites have sufficient battery capacity to withstand these eclipsesand provide full time power to all on-board electronics. The battery is an importantfactor in the life of a satellite and careful conditioning must be exercised by groundcontrol to ensure that the batteries

.10Box

(Nominal AssignedOrbital Position)

.10 Box


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Figure 2-14: Three Axis or Body Stabilized Spacecraft

Propulsion

The process by which a satellite is launched and placed in orbit is beyond the scope ofthis training course. However, the uplink operator should be aware that a satellite has apropulsion system. An Apogee Kick Motor (AKM) is on board and is used as a retro-rocket to slow the satellite at its proper apogee (22,300 miles above earth) as it crossesthe equatorial plane (see Figure 2-15). That is the only function of the AKM.

A system of small thrusters with a supply of hydrazine fuel is also on board. Thesethrusters can be used to make corrections to a slight error of the main booster system orAKM firing. Should such a need exist for these thrusters, valuable fuel would beconsumed and detract from the available fuel for its main function of station keepingand attitude control.


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There are several factors in space to force a satellite out of a geostationary orbit. Themost important ones are: 1) gravity from objects other than earth in our solar system, 2)solar winds, and 3) thermal gradient in the satellite. Imperfections in the stabilitysystem necessitate occasional correction in attitude control.

As indicated earlier the FCC mandates a maximum excursion of a satellite to 0.05

inboth north-south and east-west station keeping (the box). To maintain the satellite inthe box, fuel is used. A great deal more fuel is used to maintain the vertical (north-south) position in the box than is used to maintain the horizontal position (east-west),

Sometimes, when a satellite runs low on fuel, the satellite operator will cease north-south stationkeeping. The satellite will gradually trace what appears from earth to be afigure 8 trajectory within the assigned box. This figure 8 will increase by 0.9 degreeper year. Satellites in such an orbit are called inclined orbit satellites. Figure 2-15depicts the geometry of orbital inclination and Figure 2-16 shows the daily track of sucha satellite as seen from one earth location.

Figure 2-15: Geometry of Orbital inclination


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Figure 2-16: Representative daily satellite path of an inclined orbit satellite

Telemetry and Control

A telemetry system of sensors and a transmitter monitors the health and conditions ofvarious elements in the spacecraft. A command receiver and the actuators to controlvarious elements in the spacecraft are also included. The telemetry transmitters andcommand receiver are connected to an omnidirectional antenna so that communicationwith the TT and C ground station can be maintained during launch and in emergencies.It is worthwhile to note that several commands can affect an uplink station. In mostsatellites, ground controlled attenuators can affect the amount of power required fromthe uplink station. In extreme circumstances, if an uplink station is causing harmfulinterference, transponders can be turned off thereby cutting the desired channel ofcommunication.

The Communications Payload

The term bent pipe, used in the introduction of this chapter, was a greatly exaggeratedsimplification of a communication satellite. It is analogous to a microwave repeater of

the heterodyne type, in which, the microwave carrier is merely displaced in frequencyand retransmitted without demodulation or further processing. Most current satellitesare of this type, although some specialized satellites have been implemented in Europewhere on-board processing can increase the communications capacity, by utilizing themaximum available power.


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Figure 2-17 is a greatly simplified block diagram of a satellite repeater. It should benoted that there are three main subsystems. They are: 1) wideband receiver that iscommon to all channels, 2) antenna subsystem also common to all channels, and 3) ameans for channelization of the signals. For frequency reuse, by polarization isolation,items 1 and 3 are replicated. The antenna is common to both polarizations. The term

transponder is a contraction of the words transmitter and responder. The owner orlessee of a transponder of a 24 channel satellite is therefore an owner or lessee of 1/24 ofthe common equipment, and one of the active transmitters.

Figure 2-17: Simplified Block Diagram of Communications Payload

Wideband Receiver

The concept of using a single wideband receiver to accommodate the full frequencyrange of input signals of a communications system is unique to satellite design.Figure 2-18 depicts the elements contained in this subsystem. Usually, this

subsystem is redundant on a 1:1 basis, which means that a frequency reuse systemcontains four such subsystems.


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Figure 2-18 Typical Wideband Satellite Communications Receiver.

A highly stable oscillator consisting of a quartz crystal oscillator and multiplier producea (low side) local oscillator where:

FLO= FUP FDOWN

This maintains an upright downlink signal. The stability is such that the most critical ofnarrowband transmissions and transmissions with critical phase noise requirements arenot materially affected. Sufficient gain elements are included to drive the channelizedtransmitters to saturation.

The uplink operator should be aware of the fact that the design is such that tolerableintermodulation is maintained with the nominal levels to obtain saturation of thechannelized transmitters. It is therefore important that the uplink station operate atnominal power dictated by the satellite operator. Too much power could cause harmfulinterference to other users on the same polarization through intermodulation distortionin this wideband portion of the satellite. Figure 2-19 shows how two signals create an


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interference signal due to intermodulation, and how the intermodulation componentsare affected if one of the signals level increases. Figure 2-20 shows the effects frommore than two signals.

Figure 2-19 Intermodulation Effects.

Channelization

The concept of channelization was introduced earlier in this chapter (2.3). Reference tofigure 2-17, will show in a general way how channelization is accomplished in a satellite.The series of circulators and filters to the left of the amplifier constitutes what is knownas an input multiplexer. The function of the input multiplexer is to: 1) efficiently

transfer all signals to the separate amplifiers (circulator function), and 2) pass thedesired signal and reject the unwanted signals to the separate amplifiers (filter function).The uplink operator at this point must realize the importance of the fact that the outputof his (or her) station should be contained in the channel which has been assigned to thatstation. The uplink signal should be at the proper frequency, and be relatively freefrom spurious outputs or overmodulation (splatter), which can get into other satellitechannels.

(a)

f4 f1 f2 f3f3and f4are intermodulation products produced by third order distortion due to equal level

input signals f1and f2

(b)

f4 f1 f2 f3

If one of the input signals of condition (a) above is increased by X dB, the intermodulation

products are affected as shown.

f3=2f2-f1f4=2f1-f2

X dB increase

X dB increase

2 X dB increase


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Figure 2-20: Intermodulation Effects from Multiple Carriers

The amplifier in the block diagram constitutes the active transmitter in therepeater chain. It is usually a traveling wave tube amplifier (TWTA), although insome satellites, solid-state power amplifiers (SSPA) are used. The need forreliability in this transmitter is obvious. Redundancy is included in modern

satellites. Normal protection is 5:4 or 3:2 meaning that one spare is available for4 or 2 operating amplifiers, respectively. Ground controlled attenuators areincluded in the channels.

Transponder Amplifiers typically consist of two amplifier stages and a commonelectric power conditioner (EPC):

1 The first stage is the Driver Amplifier (DA)


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Typically, the DA is a high gain, low power, broadband, solidstate amplifier

The DA provides the commandable gain control for thetransponder

Some DA units also have an automatic level control circuit that

maintains the output signal level constant as the input signal levelvaries over a large range2. The second stage is the Power Amplifier (PA)

Typically, the PA is a high gain, high power, broadband amplifier The PA provides the RF power required for the downlink EIRP Some PA units also have a linearizer that functions to optimize the

phase & amplitude and which permit the transponder to operateat reduced backoff for the same level of intermodulation products.

The amplifiers have an input/output characteristic generally common to all amplifiers.A typical input/output curve is shown in figure 2-21. Of special interest to uplinkoperators is the fact that SSPAs will have a slightly different saturation characteristic.The TWTA type has a soft saturation whereas the SSPA has a harder saturation. The neteffect is that the SSPA will have a slightly greater linear range than the TWTA, and theoutput will droop less with input drive beyond saturation. From the uplink operationstandpoint, he (or she) should realize:

Figure 2-21 Typical Input/Output Amplifier Characteristic.


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1. For a single carrier in the amplifier, increasing the uplink power will not increasethe output power beyond saturation. Beyond saturation, the output power willprobably decrease.

2. For multiple carriers in the amplifier, the satellite operator will operate the

amplifier with less than maximum total output power (back off) in order to controlintermodulation in the amplifier. The actual back off power is at the discretion of thesatellite operator and normally varies from 2.5 to 4 dB. The satellite operator in this casewill normally assign the amount of power taken from the satellite by each carrier. Thisis controlled by the users uplink power.

In any case, the uplink station should operate with the assigned power output and notexceed assigned levels, because to do so would drive the amplifier into saturation, andintermodulation interference would be generated which would degrade or disruptservice to all users in the transponders.

Again referring to figure 2-17, the filters on the output of the amplifier are used toefficiently transfer energy from the amplifiers to the antenna. This complement of partsis known as the output multiplexer.

Antenna Subsystem

From synchronous altitude, the earth subtends a solid angle of about 19. To transmitand receive signals to and from earth would require an antenna with this beamwidth.This could be accomplished with a simple flared waveguide horn. Indeed this kind ofsimple horn antenna is used in international satellites for global coverage. For domestic(U.S. or foreign) systems, such an antenna would not only be wasteful of power, it

would seriously hamper the number of satellites which can be used for domestic service,or place an unreasonable burden on earth stations accessing those satellites. In the caseof the Continental United States (CONUS), a beam with about 3(North-South) and 8(East-West) is required.

Figure 2-22 shows in a general way how shaped beams can be formed using a singleparabolic reflector and a multiplicity of feed horns. Figures 2-23 shows how adomestic land mass (Mexico) can be efficiently covered by use of beam shaping anddemonstrating that a Shaped Beam is More Efficient than an Elliptical Beam.

.


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Figure 2-22 Generation of a Shaped Beam Antenna Pattern Using MultipleFeed Horns and an Associated Feed Network.

Figure 2-23 Spacecraft Antenna Beam Shaping Coverage of Mexico


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In the case of U.S. domestic satellites, some satellites have antennas that have coveragethat is more favorable to densely populated areas. Other satellites have east and westspot beams. Still other proposed satellites have time zone beams. Almost all have verynarrow spot beams covering Hawaii or Puerto Rico. Some proposed systems utilizingtime zone beams, can use the spatial or geographic isolation in the beams to re-use the

same frequencies in addition to re-use though polarization isolation.

It should be apparent that as the beamwidth of a satellite antenna system is narrowed bybeam shaping or by use of large antennas, there is a concomitant requirement forstability in antenna pointing and/or attitude control. A shaped beam antenna will havea steep drop off at edges of coverage as compared to a simple beam. The operator of afixed earth station should be in contact with the satellite operator to know what thevariation in coverage might be. For satellites with ground beacon pointing, thevariations will be minimal. For satellites with earth and sun sensors, the variationscould be substantial at the edge of coverage.

Satellite Characteristics (Footprints)

So far in our study of the basic concepts, we have generalized about directionalantennas, and satellite specific items such as orbit and orbital control, and the variousspacecraft subsystems as to how they relate to the uplink operator. In this section, wewill be more specific about the important satellite characteristics that are sometimescalled footprints. These characteristics are important in determining the ultimateperformance of a satellite link. For the uplink, the important characteristics are the Gainto Temperature Ratio (G/T) and the Saturation Flux Density (SFD). The two are related,and a single footprint can characterize both. On the downlink, the single importantcharacteristic is Effective Isotropic Radiated Power (EIRP).

Saturation Flux Density (SFD, and G/T)

In any radio link, the amount of transmitted power required for a certain desiredperformance, is dependent on the losses in the link and the sensitivity of the receiver(absent external interference). In a satellite uplink, the amount of power required isdependent on the location of the station relative to the satellite because: 1) the slantrange to the satellite is different (although slight) and, 2) there is a directive antenna onthe satellite, whose gain will vary depending on the direction of the earth station withrespect to the direction of maximum gain.

The concept of flux density can be explained by reference to figure 2-24. From the

satellite, the earth station antenna, for all practical purposes, looks like a point sourcewith an effective isotropic radiated power in the direction of the satellite. This powermust traverse a distance d. From the inverse square law, the power at the satellite is

reduced by, 1/ ( )24 d . The power flux density at the satellite is therefore:


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EIRP

Point Source p (Power flux density)Radiator

( )lawsquareinversefromdEIRP

p 24 =

Figure 2-24 Power Flux Density.

( )[ ]

=

2

2

24log10

m

dBWddBWEIRP

m

dBWp

where: dis synchronous altitude in meters = 3.59 x 10

7

meters

p= ( )[ ]2

09.162m

dBWdBWEIRP

The term 1/ ( )24 d represents isotropic loss in the link and is independent of frequency.It is a convenient number, as we shall see in the link analysis that follows.

Fortunately, satellite operators simplify the problem by publishing footprints of the SFDand/or the G/T. Figure 2-25 is a footprint of G/T for transponder 23, a 36 MHz C bandtransponder on Galaxy 4 (no longer in operation).

NOTE: A user of a satellite transponder (owner or lessee) or an entity in seriousnegotiation for purchase or lease is entitled to obtain Transponder Specific Footprints.

Distance d


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Figure 2-25 Galaxy IV Transponder 23 G/T (dBK).

As examples of how a G/T footprint can be used by an uplink operation consider:

1. An earth station in Seattle wishes to access Galaxy IVtransponder 23 totransmit a wideband television transmission (saturated carrier). It has anantenna with a 10 meter diameter whose gain is 53 dB, and there is a 3 dBloss between the HPA and the antenna. What HPA power output isrequired? The spacecraft has a 6 dB attenuator in the transponder used.

Solution:

From figure 2-25;

(a) The G/T in Seattle is:

+2 dB/K

(b) Therefore,

SFD = - (+2 + 89) + 6 (Pad) = - 85 dBW/m2


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(c) Now:

SFD = (EIRP 162.1) dBWm2

and

EIRP = (PA+ GA) dBW

PA = (PT 3) dBW

(d) Therefore PT= (SFD + 162.1 GA+ 3) dBW

= - 85 + 162.1 53 + 3= 27.1 dBW= 513 watts

2. An earth station in Honolulu is accessing Galaxy 4 transponder 23, 36 MHz

transponder with a radio (audio) signal utilizing 5% of the available power inthe satellite. In this (partial transponder) service, Galaxy 4 operates thistransponder with a total output power back off of 5 dB which corresponds toan input power back off of 9 dB. The earth station antenna gain is 53 dB andthe transmission line loss is 3 dB. What transmitter power is required? Thespacecraft has a 3 dB attenuator installed in this channel.

Solution:

From Figure 2-25

(a) The G/T in Honolulu is 5 dB/K

(b) Therefore,

SFD = - (-5 + 89) + 3= - 81 dBW/m2

(c) But, input signal is reduced by the input back off (from saturation), plus thepower division loss.

FD = SFD BOI PD

(d) Since the carrier takes only 5% of the total available power,

PD = 10 log .05 = -13dB

(e) Flux density at the satellite is:

FD = 81 13 9= 103 dBW/m2


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(f) The power from the transmitter is:

PT= 103 + 162.1 53 + 3= 9.1 dBW= 8.1 Watts

It should be noted that the G/T footprint of Figure 2-25 represents a specific transponderon Galaxy 4. Most operators have in their data bank actual footprints for a particulartransponder. In some cases, data resides in computer memory and specific SFD or G/Tinformation can be obtained based on the geographic coordinates of the uplink station.

Another factor that should be noted is that in the calculation of isotropic loss,

24

1log10

d

The distance used was the synchronous altitude of a satellite, not the slant range fromearth station to satellite.

Effective Isotropic Radiated Power (EIRP)

By definition, EIRP is the product of power into an antenna and the gain of the antennareferenced to an isotropic radiator. Up to now in this course of study, we have used theterm EIRP, but we have only considered the maximum or on-axis gain of directionalantennas. We have also discussed the nature of directional antennas where a beam isformed along with unavoidable sidelobes. In the section on satellite antennas, wediscussed beam shaping techniques. In an ideal situation, the spacecraft antennadesigned would like to shape the beam for uniform gain over the coverage area withlow loss. We live in an imperfect world and coverage is not uniform. EIRP shouldproperly be expressed as:

EIRP = PAGA ( ) Where is the angle off boresight and GA () is antenna gain at angle .

This concept is important in the future discussion on earth station antennas and theirpotential for interference to other systems.

Satellite operators publish EIRP footprints. Figure 2-26 is such a footprint fortransponder 23 on Galaxy 4. EIRP footprints apply to the saturated EIRP from thesatellite. If an uplink station does not drive the transponder to saturation, or if itoverdrives the transponder, the EIRP will be reduced in accordance with Figure 2-21.

Satellite EIRP applies to the downlink signal, and therefore represents an importantparameter in the design of a receiving earth station.


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Figure 2-26 EIRP Footprint.

Noise

Noise in the context of this course of training is defined as any undesired signal in acommunication circuit. The discussion deals with two basic categories of undesiredsignals. They are: 1) thermal noise, and 2) interference noise. In our treatment ofthermal noise, we will include a category called antenna noise because in satellite

technology it is intrinsic and has the same characteristics as thermal noise. Interferencewill be treated in more detail in later sections dealing with the overall satellite link.

Thermal Noise

Thermal noise is a result of random electron motion. It is characterized by a uniformenergy distribution over a given frequency bandwidth, and a normal or Gaussiandistribution of levels. In our treatment of thermal noise, we will use the temperaturescale normally used in scientific work dealing with the MKS system of measures. This isknown as the absolute or Kelvin scale. There is a one-for-one correspondence with theCelsius scale. The relation is:

Kelvins = C + 273.18

At absolute zero degrees (0K or 273.18C), there is no molecular motion. Nomolecular motion means no thermal noise.


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Thermal noise power is proportional to bandwidth and absolute temperature. Theconnecting relationship is Boltzmanns constant and is mathematically expressed as:

N (noise power) = kTB

where: k is Boltzmanns constant 1.38 x 10 23Joules/K, T is temperature inKelvins, and B is effective noise bandwidth in Hz.

Noise factor is a measure of the noise produced by a practical network compared to anideal network (i.e. one that is noiseless). Another way of defining the term is the amountof excess noise on the output of a device over the amount of noise that would be presentif the device were ideal.

Expressing this in a formula

Noise Factor = NF =

ideal

practical

N

N

An ideal (noiseless) receiver would have on its output a noise power of:

N ideal= GkT0B

Where T0is ambient temperature, G is gain of the receiver, kis Boltzmanns constant,and B is the effective noise bandwidth in Hz.

A practical receiver would have an equivalent input noise temperature Teand theoutput noise due to its internal noise would be:

N int= GkTeB

The output of the practical receiver therefore is:

N pract= N ideal+ N int= Gk (T0+ Te) B

Noise Factor =BGkT

BTTGk e

0

0 +

=0

0

T

TT e+

=0

1T

Te+

or alternatively, the equivalent noise temperature:


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Te= T0(NF 1)

Noise figure is the noise factor expressed in decibels:

F dB= 10 log 10NF

Example: A receiver has a noise figure of 1.5 dB. What is its equivalent noisetemperature?

NF = alog 4125.11010

5.1 15. ==

Te = 290 ( ) K= 12014125.1

Antenna Noise

One of the least understood aspects of satellite technology by practitioners is the conceptof antenna noise. The question arising most frequently is, How can a passive devicecreate noise? The answer lies in the fact that the environment in which the antenna isplaced is not free from noise and therefore in addition to picking up the desired signal,the antenna also picks up this noise. In most terrestrial microwave applications thisnoise is small compared to the receiver noise and for all practical purposes, it can beignored. However, in a satellite application it represents a substantial part of the totalsystem noise.

As indicated above, the environment is polluted by a variety of radio frequency energy.Most of these pollutants meet the test of the definition for thermal noise given above.That is, it has a uniform frequency spectrum and has a Gaussian level distribution.Some noise is man-made as a result of electric motors, neon signs, power lines, ignitionsystems and a plethora of industrial, scientific and medical instrumentation.Fortunately, virtually all of this type of pollution is at low frequency and is not a factorin satellite communication. Broadcast applications and HF communications (2 to 30MHz) are plagued with man-made noise and it is even extended into the VHF and UHFfrequencies in some urban areas. In satellite microwave systems however, the noise inthe environment comes from natural sources.

Under normal conditions, there are three major contributors to antenna noise in asatellite receiving system. They are: 1) galactic noise, 2) reflections from a hot earth and3) moisture absorption in the atmosphere.

In an earlier section, we discussed the abnormal situation called sun outage,where theradiation from the sun can completely overwhelm the satellite signal.

Galactic noise arises from a universe that has an almost infinite number of stars invarious stages. At 4 GHz the range of galactic noise is 8 to 12K for practical antennas.


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The earth temperature varies by a small amount around 17C (290K). This energyarrives at the antenna output terminals through the sidelobes of the antenna and isreduced by the sidelobes. The amount depends on sidelobe levels and the elevationangle. It may be of some interest to note that the antenna on board a domestic satellitehas a minimum noise temperature of 290K since it points at the earth.

Moisture in the atmosphere contributes a significant amount of noise, particularly atcertain frequency bands, as discussed previously. The amount of noise contributed alsodepends on elevation angle in that the length of the path through the moisture ladenatmosphere decreases as elevation angle increases. Figure 2-27 graphically shows hemajor contributors to antenna noise in the satellite receiver. For high elevation angles(more than 20 degrees), noise is fairly constant between 20 and 30 degrees Kelvin.

Figure 2-27 Major Contributors To Antenna Noise In The Satellite Receiver.

Receiver Noise Temperature (Clear Weather)

The block diagram of Figure 2-28 shows a receiver consisting of: 1) antenna andfeed, 2) losses (L1) between antenna and LNA, 3) LNA 4) losses (L2) between LNAand receiver/demodulator and 5) receiver/demodulator. Loss factor L1consists ofresistive feed and waveguide loss and mismatch loss that arises from imperfect

impedance match between antenna and LNA.


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Figure 2-28: Block Diagram Showing Satellite Receiver Noise Contributions.

Loss factor L2 consists of cable and/or power divider losses between LNA and thereceiver/demodulator.

Referenced to the input of the LNA, the effective noise temperature of the system iscalculated as follows, using the equation in figure 2-28.

Where To is ambient temperature in Kelvins (290 K)L1is loss (power ratio)Tais antenna noise temperatureTpis LNA noise temperatureL2is loss (power ratio)

Gpis gain of LNATris receiver noise temperature

Practical values for these factors are:

Ta= 30 K (elevation angle greater than 20)L1= 0.2 dB = 1.047L2= 10 dB = 10Tp= 120 KGp= 50 dB = 100,000Tr= (noise figure of 15 dB = 290 (31.6 1) = 8880

( ) ( ) ( )( )

000,100

888010

000,100

290110120

047.1

2901047.1

047.1

39+

++

+=effT

Teff= 28.6 + 13 + 120 + 0.026 + 0.888

= 162.5k

If the losses L1 and L2 are 0 dB (1.0), the expression reduces to:


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R

Rpaeff

G

TTTT ++=

= 30 + 120 + 0.09 = 150.09K

Power Addition of Noise

Since noise is random in nature, addition of two or more noise signals is done on apower (incoherent) basis. Thus,

Nt= N1+ N2- - - - +Nn

Example: N1= -30 dBmN2= -40 dBm

( )43 1010log10 +=GN

= 0011.log10

= -29.586 dBm

Satellite Access Methods

The term satellite access is used to describe the method employed to permit multipleusers to utilize a satellite transponder. In general, three different methods of satelliteaccess are in use today: Frequency Division Multiple Access, or FDMA, Time DivisionMultiple Access,

Documents

NAB Uplink Operator SeminarR9