PRINCIPLESPRINCIPLESPRINCIPLESPRINCIPLESPRINCIPLES

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COMMUNICATIONCOMMUNICATIONCOMMUNICATIONCOMMUNICATIONCOMMUNICATION

ENGINEERINGENGINEERINGENGINEERINGENGINEERINGENGINEERING

(For B.E./B.Tech. Students)

ANOKH SINGHDepartment of Applied Electronics and

Microwave TechnologyPusa Institute, New Delhi

A.K. CHHABRAB.Tech, MISTE

Department of Electronics EngineeringDirectorate of Training and Technical Education,

New Delhi

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© 1984, Anokh SinghAll rights reserved. No part of this publication may be reproduced, stored in a retrievalsystem or transmitted, in any form or by any means, electronic, mechanical, photocopying,recording or otherwise, without the prior permission of the Publishers.t

First Edition 1984Subsequent Editions and Reprints 1987, 91, 94, 97 (Twice), 99, 2000, 2001, 2002, 20032004, 2006, 2007, 2008, 2009, 2010, 2012Reprint with Corrections 2013

ISBN : 81-219-0476-5 Code : 10A 045PRINTED IN INDIA

By Rajendra Ravindra Printers Pvt. Ltd., 7361, Ram Nagar, New Delhi -110 055and published by S. Chand & Company Ltd., 7361, Ram Nagar, New Delhi -110 055.

PREFACE TO THE REVISED SEVENTH EDITION

The revised edition of this book provides a comprehensive coverage of the latest topics of thefield of electronics communication. Although nothing has been omitted from the previous editionthere are significant addition of the topics such as Cellular Mobile Communication, Digital DataCommunication, Computer Communication, Radio Paging System, DTH, IPTV, Wi-fi, ConsumerElectronics and Advanced Communication Systems.

The revised edition is presented in simple and easy to understand language with more illustrations.This revised edition meet the latest syllabus of different engineering colleges and universities. Thebook is quite useful for students preparing for various courses in communication Engineering,professional like Engineering services etc. The book is equally useful to the students of B.Sc, M.Sc.and M. Tech. (Electronics). A good numbers of valuable suggestions were received from the subjectexperts which has been incorporated in this edition.

I am thankful to Dr. H.S. Shiveram, Head Communication, NIE, Mysore, Prof. D.P. Chakraborthy,MPCT (Gwalior) (M.P). Shri N.L. Narayan, MIT Aurangabad, Shri S.P. Singh, Controller, BTE, Delhi.M.S. Mageshwari, Niketan Engg. College, Thimmarasanaic, Kanpor, Anadipati, Shri DNK Gauri, ShriA.K. Gupta, Shri Dipankar Misra, Shri Mukesh Saxena, M.S. Geeta Bhatia, Lecturers Delhi for theirvaluable suggestions.

The author is thankful to Mrs. Nirmala Gupta, Chairperson & Managing Director, Shri NavinJoshi, Vice President (Publishing) and entire editorial department of S. Chand & Company Ltd. forbringing and this revised edition in an attractive format. While every care has been taken to present anerror-free text, but sometimes errors do creep in unintentionally, for which I have to depend on ouresteemed students, teachers for the feedback. The advice and suggestions to improve the text are alsowelcome and will be highly appreciated.

A.K. CHHABRA

iii

PREFACE TO THE FIRST EDITION

The main objective of the book is to bring out broad outlines of different types of electroniccommunication systems. The book presents to the students of Communication Engineering informa-tion about the basic processes, principles and philosophies of different communication systems. Thebook will be quite useful for students preparing for various courses in Communication engineering,professional like Engineering services etc. It can also prove equally useful to the students of M.Sc.(Electronics).

The first four chapters of the text describe different types of signals, modulation and demodu-lation of these signals, various transmission channels and noise encountered by the signals duringpropagation from sender to receiver end. Apart from this, this part of the book also deals with differentforms of line communication systems. A brief introduction of information theory is also given at theend of the text so that the students become familiar with this aspect of communication systems.

Radio communication systems form the next part of the book and is dealt with in Chapter V andVI under the headings Radio Transmission Systems and Radio Receivers. Different forms of radiocommunication systems such as SSB/ISB, telegraphy/telephony FM/PM and the problems encoun-tered in these systems are discussed and possible solutions are also presented in brief.

Broadband communications and Picture signal transmission/reception forms the last part of thebook. Broadband communications are covered under the topics like FDM/TDM, wire/microwavecircuits. Lastly satellite and optical communication systems are also outlined briefly. In Picture signalsystems are included topics like Facsimile, black and white/colour TV principles. This discussion,however, is limited to systems presently operating in India.

It is hoped that the book will meet the long felt needs of different categories of students.

While every care has been taken to present an error-free text, but some unintentional errorsmight have crept in at various stages and readers are requested to point out these errors. Suggestionsfor improvement of the text of this book will be most welcome.

The author is thankful to friends and colleagues who have helped in preparation of the text andgetting it typed. Finally, thanks are also due to the Publisher M/s. S. CHAND & COMPANY LTD.for bringing out the book within the shortest possible period.

ANOKH SINGH

v

CONTENTS

1. Signal 1–58Types of signals; Analogue and digital signals; Spectrum of signals; Telecommu-nication services; Transmission paths; Signal analysis; Orthogonality; Orthogo-nality in complex functions; Mean square error; Legendre polynomial land; Fou-rier series; Trignometric and Exponential Fourier Series; Complex Fourier spec-trum; Fourier transform; Properties of Fourier transforms; Convolution theorem;Parseval’s theorem.

2. Switched Communication Systems 59–138Introduction; Basic system structure; Telegraphy—telegraph instruments; Singlecurrent and double current circuits; Duplex; Quadruplex and duplex circuits; Tele-printer; Telephony—Telephony instruments; Telephone sets; Electronic Telephone;Transmission bridges; Telephone relay; Local battery exchange; Central batteryexchange; Automatic telephony – Uniselector and two motion switches; Strowgerexchange; Line finders; Trunking Diagrams; Director systems; Cross-bar switchand exchanges; Electronic Telephone exchanges; Subscriber Line interface circuit(SLIC); Stored program control (SPC); Advantages of digital transmission; Trafficand Trunking; Grade of Service; Limited availability

3. Modulation 139–186Introduction; Amplitude modulation; Amplitude modulation circuits; Van Der Bijlmodulator; Collector modulation; Balanced modulator; Ring modulator; Vestigialside-band systems; Frequency modulations; Frequency modulation circuits; Tran-sistor reactance modulation; Phase modulation and modulation circuits; Multi-plexing; Frequency division multiplexing; Time division multiplexing; SamplingTheorem; Pulse modulation; PAM; PWM; PPM

4. Demodulation 187–200AM detectors; Envelope detection; Practical diode detector; VSB demodulators;Synchronous detector; Phase-Locked Loop (PLL); FM discriminators - Fosterseeley discriminators; Ratio detector; PLL frequency discriminator; Demodula-tion of phase modulated waves.

5. Digital Data Communication 201–218Introduction; Digital communication system; ASK; Coherent ASK detector; Non-coherent ASK detector; FSK Demodulation of binary FSK wave; Detection ofFSK using PLL; PSK; Detection of binary PSK waves; Differential PSK (DPSK);Quadrature of Phase shift keeying (QPSK); QPSK demodulator; M-Ary PSK; M-Ary PSK transmitter; M-ary PSK receiver; Elements of Digital CommunicationSystem; Advantages of digital communication; Pulse code modulation; Differen-tial PCM (DPCM); Delta modulation; Adaptive delta modulation.

6. Radio Transmission Systems 219–259Introduction—AM transmitters; Broadcast transmitters; MO circuits; Buffer am-plifier; Harmonic generators; Power amplifiers; Neutralisation; Power supply;Cooling of transmitter tubes; Radio telephony transmitters—Automatic modula-tion control; Volume compressor; Peak clipper; Echo and echo suppressors; Sing-ing and singing suppressors; Terminal equipment; Privacy devices; Quiescent cur-rent working; SSB transmitters—ISB working; Radio telegraphy transmitters; FMtransmitters; FM stereo Transmitter; Pre-emphasis circuit.

vii

7. Radio Receivers 260–297TRF and Superhetrodyne receivers; AM broadcast receivers—RF amplifier; Fre-quency changers; IF amplifier; Detector; AGC Audio amplifier tone control; Com-munication receivers—variable selectivity; Noise limiter; Squelch; AFC; Tuningindicator; Volume expander; SSB receivers; Diversity reception – Space and fre-quency diversity reception; FM receivers; Stereo FM receiver; Measurement ofreceiver performance; Selectivity; Sensitivity Fidelity; Signal to noise ratio; Noisefigure.

8. Noise 298–330Introduction; External noise; Internal noise; Thermal agitation noise; Shot noise;Noise figure; Noise figure measurement; Noise figure in amplifiers; Noise tem-perature; Noise in communication systems; Noise in AM, FM and PM systems;Noise in pulse modulated systems.

9. Transmission Lines 331–390Introduction—Open wire lines; Coaxial cables; Strip and microstrip lines; Waveguides; General line equations; Classification of lines; Loading; Reflection; Standingwaves; Impedance matching in lines; Stubs; Smith chart; E and H fields; Bound-ary conditions; Wave front; Wave guides—Group and phase velocity; Guide wave-length; Wave guide modes; Mode excitation; Circular wave guides.

10. Aerials 391–437Introduction; Radiation from a short dipole and power radiated by it; Radiationfrom a short grounded aerial; Effective height; Ground systems; Antenna excita-tion; Short wave and medium wave aerials; Horizontal dipole; Long wire; Vee andrhombic antenna; Antenna arrays; Broadside and end-fire array; Power gain andbeam width; Parasitic array; Log-periodic array; Turnstile and super-turnstile an-tenna; Discone antenna; Discone Antenna; Microwave aerials—Parabolic and hornantenna; Reciprocity Therorem; Receiving antenna—Loop and ferrite rod antenna.

11. Propagation of Radio Waves 438–469Reflection/refraction of radio waves; Ground waves; Atmospheric absorption—Tropospheric scatter; Ionospheric layers; Sky waves; Virtual height; Regular andirrregular ionospheric variations; Skip distance; Fading and echo-scattering; Cata-strophic disturbances; Primary and secondary service area.

12. Broad-Band Communications 470–490Time division multiplexing; Frequency division multiplexing—3-channel and 12-channel carrier system; Computer communication systems; Microwave links—Line of Sight (LOS) links; Tropospheric links—Quadruple diversity system; Inte-grated service digital network (ISDN); Local Area Network (LAN); Private BranchExchange (PBX);

13. Satellite Communications 491–499Introduction; Satellite communication system; Satellite orbits; Basic componentsof satellite communication; Constructional features; Commonly used frequences;Communication package; Satellite communication in India.

14. Fiber Optic Communications 500–507Optical communication; Basic fiber optic system; Advantages; Optical fiber con-struction; Modes of propagation; Numerical aperture; Losses in optical fiber; Op-tical communication system.

viii Contents

15. Picture-Signal Transmission and Reception 508–529Facsimile-transmission and reception; Index of cooperation; Television-scanningprocess; Interlaced scanning; Composite video signals; CCIR- B standards; TVcamera systems—image orthicon and vidicon-transmission and reception principlefor black and white TV signals; Principle of colour TV—primary colours; Chromi-nance and luminance signals; Colour TV systems—NTSC, SECAM, PAL, trans-mission and reception using PAL system; PIL picture tube; HDTV; LCDTV

16. Radar and Navigation 530–551Introduction; Basic Radar Systems; Radar Systems; Radar range; Pulsed RadarSystem; A-Scope; Plan Position Indicator (PPI); Search Radar; Tracking Radar;Moving Target Indicator (MTI)—Doppler Effect; MTI principle; Digital MTI; Ra-dar Beacons; CW Droppler Radar; Frequency Modulated Radar; Loop Antenna;Errors in Loop Direction Finding; VHF Omni-Directional Range (VOR); LORAN;Distance Measuring Equipment (DME); Instrument Landing System (ILS); GroundControlled Approach System (GCA).

17. Sound and Accoustical Systems 552–582Introduction. Nature of sound; Frequency range and harmonics; Intensity anddynamic range; Sources of sound programme; High fidelity and realism; Stereo-phony; Microphones; Types—Dynamic; Ribon; Crystal; Capacitor; Methods ofdriving the diaphragm; Pressure—Gradient operation; Directivity patterns—omniand bidirectional; Loudspeaker horn type; Loudspeaker enclosures; Sound Re-cording; Magnetic Tape Recording—Tape transport mechanism; Capstan drives;Tape speed; Wow and flutter; Clutch; Friction brakes; Alignment of tape and heads;Magnetic principles; Magnetic heads—Record; Replay and erase heads; Othercomponents—Record amplifier; Replay circuit; Ultrasonic bias; Optical Record-ing—(i) variable density (ii) variable intensity type; Disc Recording; Accoustics ofBuildings—Equation for decay of sound in an enclosure; Equilibrium inensity;Reverberation time; Accoustical designing of buildings.

18. Basic Information Theory 583–593Introduction; The discrete channel; Redundancy channel capacity; Coding Dis-crete noisy channels—Coding in discrete noisy channels; Parity check coding;Algebraic coding; Continuous signal; Bandwidth—Signal to noise ratio trade off.

19. Recording and Digital Processing of Video Signals 594–618Basic Video recording principles; Tape speed; Head gap G and recorded wave-length ; Helical video recording; Frequency response of recording heads; Re-cording of luminance signals; Recording of chrominance signal; High density re-cording system; Azimuth recording; VHS chrominance recording systems; Fre-quency range of the VHS signal; Tape loading; Tape format in VHS systems; Oper-ating modes of a video cassette recorder; E-E mode; Recording mode; Playbackmode; Digital processing of Video signals; How much digital is the digital TV ?Video processor; Deflection processing; Audio processing; Control computer; CDplayers.

20. Latest in Communications 619–627Cellular mobile communication; The concept of cell; Basic cellular mobile radiosystem; The cellphone; Facsimile (FAX); Important features of fax machine; Appli-cation of Facsimile; VSAT; Radio paging system; Advantages of paging; Modem;Video-on Demand (VOD); IPTV Internet Protocol Television; Wi-Fi; What is 3GObjective Type Questions 628–657Appendix. Besel Function of the First Kind 658

Smith Chart [(for solving Transmission Line problems); Ref.Examples 9.8, 9.9, 9.13-9.15; Art. 9.5.5. and Example 9.23]

Index 659–662

Contents ix

1

SIGNALS

Communication means to share one's thoughts with others. It is commonly read in fictionstories about an instrument that reads thoughts of a person and transmits them to a recipientdirectly. Unfortunately, a considerable effort is required to formulate our thoughts into speech ora written text. Speech is considerably easier to accomplish our thoughts than writing. It is for thisreason that most people prefer the use of speech for communication with others.

Communication is a bidirectional process. One must have the feedback from the distant endin order to know what to say next. This is then the telephone system so commonly used by thepeople that communication by telephone with a person sitting thousand of miles away is takenfor granted.

But apart from telephone, there is a Telex/Telegraph system which provides communicationof written messages from one place to another. In addition, there are now in existence telemetrysystems which transmit data from one place to another where this could be stored, processed orretransmitted to other places. This is an attractive development that is leading to decentralizationof organisations. One may have different wings of his organisational set up to be physicallydistant but fully linked through communication channels.

The latest trend for communication channels is the use of digital signals for transmission ofmessages in place of analog signals.

Apart from two-way communications described above, there is another way of sharing ourthoughts with others by way of public address systems, Radio/T.V. broadcast systems. Thesesystems may be thought of as one-way communication systems having no provision for feedbackfrom the distant end.

In practice, telecommunications involve the conversion of messages which may be in theform of words or coded symbols into electrical voltage or current which varies with time and isused to carry information from one point to another. Such electrical quantities are termed assignals. These signals are then transmitted over a communication system to the receiver wherethey are converted back to the original form. Figure 1.1 shows the outlines of a communicationsystem.

The encoder converts the message into electrical signals and feeds them to the transmitter.The signals are processed at the transmitter and transmitted to the receiver. The transmission pathmay be a telephone line or free space. In the first case, the system is commonly termed as LineCommunication, while the latter is termed as Radio Communication.

Fig. 1.1. Outlines of a telecommunication system.

1

2 Principles of Communication Engineering

At the receiver end, the receiver is made to select the desired signal, process it and deliverto the decoder an electrical signal which resembles in all respects to the signal produced by theencoder. The decoder converts the signal in the form of the original message.

1.1.Types of SignalsThe electrical signals produced by encoders are of two types – the analogue signals that

continuously vary with time and the digital signals which are not continuous.The analogue signals are sinusoidal in nature with or without harmonics and represent the

variations of a physical quantity like a sound wave. The digital signals comprise of a series ofpulses that occur at discreet intervals of time.

1.1.1.Analogue Signals. A telephone, radio broadcast or TV signals are very common typesof analogue signals for use of general public. They are represented by voltage wave forms thathave different amplitudes at different instants of time.

Telephone Signals. A telephone message comprises of speech sounds having vowels andconsonants. These sounds produce audio waves which makes the diaphragm of a microphone tovibrate. To this diaphragm is attached a coil surrounded by a static magnetic field on all the sides.The motion of the coil in this field causes e.m.f. to be induced in the coil which is the electricalequivalent of the sound waves. Figure 1.2 represents the electrical signal obtained from themicrophone when the word ‘THREE’ is uttered before a microphone.

These speech signals may be broken upinto sinusoidal wave forms of differentfrequencies. Most of the energy in thesesignals is found to be contained in the rangefrom about 300 Hz to 3400 Hz and thisfrequency range is quite sufficient to recoverintelligible message from telephone signals.An overall bandwidth of 4 KHz is thereforeused for every telephone channel.

TV Picture Signals. A picture is composedof bright and dark spots called picture elementsarranged in a particular sequence. To televisepictures, these images are focused to some kindof a photosensitive screen more commonlyknown as target which is systematically scanned by an electron beam. In this way of scanning, allthe picture elements are scanned and converted into electrical signal in a particular order. At fixedintervals of time synchronising pulses are added to this electrical signal. Figure 1.3 shows theelectrical signal produced by a 625 lines TV camera.

Fig. 1.3. A T.V. signal.

Fig.1.2. Electrical signals for theword THREE.

Signals 3

If the picture width is w and height h, then ratio w/h is termed as Aspect ratio and is fixedas 4/3

4

3

w

hor h = 3w/4Since the complete picture is scanned by 625 horizontal scanning lines, the distance between

the lines or the height of a picture element is equal to 3 1

625 4 625

h w

=3

2500

w

If each picture element is assumed to be of square cross-section, then number of pictureelements per horizontal scanning line is given by

Number of elements per line = w/width of the picture element

3 2500/

2500 3

ww

Since each picture frame has 625 horizontal scanning lines and there are 25 frames scannedevery second. Total number of elements scanned per second is given by

Number of elements scanned per second 625 25 2500

3Considering the case when white and black elements are placed alternately in a picture,

then a pair of such black and white elements would make one cycle and there will be maximumnumber of cycles in this particular case.

Maximum video frequency 625 25 25002

3 = 6.51 MHz

A number of lines are lost during vertical blanking period which occurs twice in a pictureframe. Similarly, a time is lost in horizontal retracing period during which no scanning take place.Lastly such a fine detail is never required in a picture. Considering all these factors, a bandwidthof 5.0 MHz is used as a compromise in India.

Radio Broadcast Signals. Another very important analog signal is the radio broadcastsignal used for education and entertainment of general masses. These signals may be in the formof speech or music. Though the speech signals occupy a bandwidth of 4 KHz only, the musicoccupies a considerably large bandwidth. A high fidelity music programme occupies a frequencyband that extends from 20 Hz to 16 KHz giving a bandwidth of 16 KHz approximately. Thus, ahigh fidelity (Hi–Fi) music programme occupies as much channel band width as is required byfour telephone channels.

For ordinary radio broadcast music and other programmes, a frequency bandwidth of 5 KHzis usually employed.

1.1.2. Digital Signals. Digital signals comprise of pulses occurring at discrete intervals oftime. The pulse may occur singly at a definite period of time or as a coded group. These signalsplay a very important role in the transmission and reception of coded messages. Simplest types ofdigital signals are the Telegraph and Teleprinter signals but sometimes analog messages are alsoconverted into digital form before being transmitted for certain reasons which are discussed in alater section.

Telegraph Signal. A telegraph and teleprinter are the most common instruments that are usedto transmit written texts in the form of coded signals. Codes are allotted to different characters.

4 Principles of Communication Engineering

The simplest form of telegraph circuit consists of a Telegraph Key which switches on thecurrent into the line when it is pressed and stops the current when the key is released. The intervalfor which the current flows is termed as the MARK interval and the state of zero current is termedas SPACE interval. Such a telegraph signal is shown in Fig. 1.4 (a). This system is termed asSINGLE CURRENT working.

Fig. 1.4 (a). Telegraph signal using single current working.Another form of telegraph signal is termed as a DOUBLE CURRENT working and employs

two batteries. This system passes current in one direction during MARK but during SPACE thecurrent is reversed. Such a signal is shown in Fig. 1.4 (b).

Fig. 1.4 (b). Telegraph signal using double current working.As can be seen, the telegraph signals are in the form of pulses. The rate of transmitting these

pulses is termed as the signalling speed and is measured in ‘BAUDS’ which is defined as thenumber of pulses transmitted per second. The most common speed used in machine telegraphy isabout 50 bauds.

The pulses contained in the telegraph or other such signals may be analysed with the aid ofFourier analysis. Such an analysis shows that these pulses consist of a band of frequenciescommonly known as the ‘bandwidth’ of the signal. The bandwidth of a 50 baud telegraph signalis of the order of 120 Hz and is termed as the bandwidth of a telegraph channel. Thus, a telephonechannel with bandwidth of 4 KHz may be used to transmit a number of machine telegraphy(teleprinter) signals simultaneously. Such a system is referred to as multiplexing.

Radar Signal. A radar is a device which is used to find out the location of distant objects interms of range and bearing. This is done by transmitting a short period signal and beaming it tothe target. The reflected signal is picked up by the radar receiver and is used to determine thelocation of the object.

The radar signal shown in Fig. 1.5 is basically a train of rectangular pulses transmitted at a

Fig. 1.5. A radar signal.

Principle Of CommunicationEngineering

Publisher : SChand Publications ISBN : 9788121904766Author : Anokh Singh And AK Chhabra

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