trundle, e. (2001). newnes guide to television and video technology (3rd ed.)

Newnes Guide to Television and Video Technology Newnes Guide to Television and Video Technology Third edition Eugene Trundle, TMIEEIE, MRTS, MISTC OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Newnes An imprint of Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published 1988 Second edition 1996 Third edition 2001 # Eugene Trundle 1988, 1996, 2001 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed to the publishers. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. ISBN 0 7506 48104 Typset by Keyword Typesetting Services Ltd, Wallington, Surrey Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall Contents Preface to third edition vii 1 Basic television 1 2 Light and colour 15 3 Reading and writing in three colours 21 4 The PAL system 43 5 Transmission and reception 51 6 Colour decoding 61 7 TV display systems 78 8 The TV receiver 102 9 Teletext 122 10 PAL-Plus, MAC and enhanced TV 132 11 TV sound systems 144 12 Digital TV 165 13 Satellite TV 194 14 Cable TV 215 15 Development of video tape recording 223 16 Magnetic tape basics and video signals 228 17 Video tape: tracks and transport 239 18 Signal processing: video 263 19 Signal processing: audio 294 20 Servo systems and motor drive 308 21 System control for VCRs 324 22 The complete VCR 337 23 Analogue camcorders and home video 345 24 Digital tape formats and computer editing 359 25 Tape formats compared 382 26 DVD players 391 27 Care, operation and maintenance 399 28 Interconnection and compatibility 406 Index 417 v Preface to third edition The terms of reference for this book are very wide, and increase with each new edition. TV and video take an ever larger part in our leisure, educational and recre- ational activities; here the technology behind them is explored and explained. Much use is made throughout the book of block diagrams. Since integrated circuits ± silicon chips ± have become so widespread, much service data are now presented in block diagram form. To explain principles and techniques I have sometimes used earlier discrete circuits and systems, in which the separate func- tions and circuit elements can be clearly discerned. As this is being written the world of TV and video is in transition from analogue to digital operation in the realms of broadcast/reception, tape recording and disc systems, while a convergence of computer and TV/video technologies is under way. This is reflected in this new edition of the book, which is aimed at interested laypeople, students, technicians and those in allied fields seeking an insight into TV and VCR practice. I have assumed that the reader has a basic knowledge of electronics and mechanics. For further reading I can recommend my Television and Video Engineer's Pocket Book; and for those whose interest lies in fault- diagnosis and repair, my Servicing TV, Satellite and Video Equipment, both published by Newnes. My thanks are due once more to my patient and loving wife Anne, whose moral support, coffee-brewing and keying-in services have kept me going through the three editions of this book. Eugene Trundle vii 1 Basic television For a reasonable understanding of colour television, it is essential that the basic principles of monochrome TV are known. As we shall see, all colour systems are firmly based on the original `electronic-image dissection' idea which goes back to EMI in the 1930s, and is merely an extension (albeit an elaborate one) of that system. Although there are few black and white TVs or systems now left in use, the compatible colour TV system used today by all terrestrial transmitters grew out of the earlier monochrome formats. In the early days it was essential that existing receivers showed a good black and white picture from the new colour transmis- sions, and the scanning standards, luminance signal, and modulation system are the same. What follows is a brief recap of basic television as a building block of the colour TV system to be described in later chapters. Image analysis Because a picture has two dimensions it is only possible to transmit all the infor- mation contained within it in serial form, if we are to use but one wire or RF channel to carry the signal. This implies a dissection process, and requires a timing element to define the rate of analysis; this timing element must be present at both sending and receiving ends so that the analysis of the image at the sending end, and the simultaneous build-up of the picture at the receiver, occur in syn- chronism. Thus a television picture may be dissected in any manner, provided that the receiver assembles its picture in precisely the same way; but the path link between sender and viewer must contain two distinct information streams: video signal, which is an electrical analogy of the light pattern being sent, and timing signals, or synchronisation pulses, to define the steps in the dissection process. The presence of a timing element suggests that each picture will take a certain period to be built up; how long will depend on how quickly we can serialise the picture elements, and this in turn depends on the bandwidth available in the transmission system ± more of this later. 1 Scanning If we focus the image to be televised on a light-sensitive surface we are ready for the next stage in the dissection process ± the division of the pattern into picture elements or pixels. Each pixel is rather like the individual dots that go to make up a newspaper photograph in that each can only convey one level of shading. Thus the detail, or definition, in the reproduced picture is proportional to the number of pixels. In 625-line television we have approximately 450 000 pixels, adequate for a 67 cm-diagonal picture, but barely sufficient for much larger screens. These individual pixels are arranged in horizontal lines; there are 625 lines in the British TV system. Figure 1.1 shows how the image is scanned, line by line, to read out in serial form the pattern of light and shade which forms the picture. When half the lines have been traced out the scanning spot has reached the bottom of the picture and traced one field. It now flies back to the top of the screen to trace out the rest of the 625 lines in the spaces between those of its first descent. This is known as interlacing, and confers the advantages of a 50 Hz (Hz, Hertz, one cycle per second) flicker rate with the lower scanning speed and lesser bandwidth require- ment of a 25 Hz frame rate. All TV systems use this 2:1 interlaced field technique; its success depends only on accurate triggering of the field scan. Image sensor In earlier designs of TV camera the image pick-up device was a thermionic tube whose light-sensitive faceplate was scanned by a sharply focused electron beam. Currently a solid-state device is used, as shown in Figure 1.2. Its faceplate is made up of an array of hundreds of thousands of silicon photodiodes mounted on a chip, typically 7 mm diagonal, arranged in lines and columns. Though a real sensor of this type may contain 750 diodes per line and 575 rows, our diagram shows a 12 Â 9 matrix for simplicity. During the active field period each reversed- biased diode acts as a capacitor, and acquires an electrical charge proportional to the amount of light falling on it: the televised image is sharply focused on the sensor faceplate by an optical lens system. Each diode is addressed in turn by the sensor's drive circuit so that (as viewed from the front) the charges on the top line of photodiodes are read out first, from left to right. Each line is read out in turn, 2 Figure 1.1 The scanning process. Horizontal lines are drawn from left to right of the screen by horizontal direction, and `stacked' vertically by the slower- moving vertical deflection field [...]... of light in the top right-hand corner of the picture, and the monitor's scanning spot is in the middle of the screen when it reproduces the light, the picture is going to be jumbled up! This is prevented by inserting synchronising pulses (sync pulses for short) into the video waveform at regular intervals, and with some distinguishing feature to enable the TV monitor to pick them out To signal the beginning... In monochrome television (now largely confined to industrial surveillance and special-purpose applications) only the luminance signal and the sync and black level are modulated onto the broadcast carrier wave With the need to send a chroma signal in addition to the basic VBS (video, blanking and syncs) signal, coupled with the requirement to keep the combined signal within the channel bandwidth normally... carpet to cat and back again, each of which will give rise to a sudden transient At the other extreme, if the camera is looking at a pattern of fine vertical lines the video signal will be much `busier' and contain a great deal of HF energy In practice the frequencies in the video signal are mostly related to line and field scanning rates, and much of the energy in a video signal is concentrated into `packets'... will eliminate some of the `detail' information and also, perhaps, distort the signal in other ways If, on the other hand, the bandwidth were too great it would allow undue `noise' and other unwanted signals to enter the system and thus detract from the quality of the vision (and sound) In any case the bandwidth spread of any transmission must be limited to the minimum possible spectrum space (rigidly-kept... camera and also provides a blanking signal for use in the video processing amplifier A second pair of outputs from its sync-pulse section is taken to an adder stage for insertion into the video waveform, and the composite video signal is passed into the transmission cable On arrival at the monitor, the signal is first amplified, then passed to the cathode of the picture tube A second path is to the... transmission path is long, and subject to distortion, reflections and similar hazards for the signal It is finding increasing applications in television technology, especially in the areas of studio equipment, video tape recording, broadcasters' inter-location links, fibre-optic transmissions and domestic receiving equipment Sidebands Whatever type of modulation is used, sidebands are produced Treated... separator stage which works on an amplitude-discriminating basis to strip off the sync pulses for application to the timebase generators They work in just the same fashion as those in the camera to generate sawtooth currents in the scanning coils with which to deflect the scanning beam in the display tube Thus we have the two scanning systems ± one at the sender and one at the receiver ± swinging to and. .. transmission) to conserve valuable band space and prevent mutual interference with adjacent channels A descriptive `model' illustrating these points is given in Figure 1.11 13 14 Figure 1.11 Model showing the relationship between the sidebands and the bandwidth 2 Light and colour We know radio and TV broadcasts as electromagnetic waves whose frequency determines their wavelength, and various broadcast bands... we pass through the bands allotted to radio transmissions, then terrestrial TV broadcast and space communications Way beyond these we come into an area where electromagnetic radiation is manifest as heat, and continuing upwards we find infra-red radiation, and then a narrow band (between 380 Â 106 and 790 Â 106 MHz) which represents light energy Beyond the `light band' we pass into a region of ultra-violet... of red and green lights, which would render yellow, as in Figure 2.2 Yellow is a complementary colour It is, in fact, complementary to blue since blue was the additive primary which had to be removed from white light to produce it By similar tokens the complementaries of red and green are cyan and magenta, which means that cyan (akin to turquoise) is produced by the addition of green and blue, and magenta . Newnes Guide to Television and Video Technology Newnes Guide to Television and Video Technology Third edition Eugene Trundle, TMIEEIE, MRTS, MISTC OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE. optical fibre; the distance required to be covered; and to a lesser extent, the nature of the information to be carried. Thus the medium-wave sound broadcast band (MF, medium frequency) is suitable for. When half the lines have been traced out the scanning spot has reached the bottom of the picture and traced one field. It now flies back to the top of the screen to trace out the rest of the