' -..•■• « > Y - ; iBISIOftllllllfl.J. y B ■ '■ ■ '"•: ■'■■ • - ^": gill !■ ’ - -< Y “ A-. ::5 ' ? ££ „■ £ ■ . ■.■ ...S: .. ;Si®gKS|^^<YSaa ■..::,-:-;.:-.-:r. .. •• . ^•••■ yY^- Y?- - J ■ |.YY3ttgBS i® S«<1Y£y:<:Y’ -v;. :YJn:C;Y£ M... .;■ Y' Ay'y ' Y Y- .. -< Yd'' Y- •■ Y • Y/<YSYS:aag-Y<><YYJ:Y<YYY' Y< &YY ■ Y'< -W®==E4gES&YY®:fe;Y;: igffip£ YyY£Y;;sH^®JY;Y3yY?E::Y: ®s £77 ■■\<Y'<;;Y,Y^aY:£Y.ly YfYY- Syy'y.y ffi|iE?i|ridfflSKSYWSlY77- ■ c j ? <^iYyii®-Y, <> ■;'YYd./”-:Y'''--<®:®' / 1 "•■■■■■■ Y?Y-; - ||BS( ■• - 77/ PM 5-l:z. ’- ': -- ? # S g ffiferd dd ' ■ ■I:rdddd liil SI ■/-®®-YYYy:-''y\yy.';.' .77 : 7/ ■ BY7-Y777 t'd -Yd<Y/>d:rd;Y<'dY ' Y-;®d.......... — . 7 Y'■ ' Y-'y^ . ‘'vd dp.ifciiiii Y - ' sHidHiliBliir..i 1............... H Frontispiece: The Aerial Tower of the B.B.C. Television Transmitter at Alexandra Palace, North London {Courtesy of the B.B.C.) THE PRINCIPLES OF TELEVISION RECEPTION BY A. W. KEEN M.I.R.E.. M.BRIT.I.R.E., A.M.I.E.E. Fellow of the Television Society Formerly Jiesearch Engineer, R.F. Equipment, Ltd. Sometime Chief Instructor, No. 8 Radio School, R.A.F. LONDON SIR ISAAC PITMAN & SONS, LTD. First published 1949 Reprinted 1951 SIR ISAAC PITMAN & SONS, Ltd. PITMAN HOUSE, PARKER STREET, KINOSWAY, LONDON, W.C.2 THE PITMAN PRESS, BATH PITMAN HOUSE, LITTLE COLLINS STREET, MELBOURNE 27 BECKETTS BUILDINGS, PRESIDENT STREET, JOHANNESBURG ASSOCIATED COMPANIES PITMAN PUBLISHING CORPORATION 2 WEST 45TH STREET, NEW YORK SIR ISAAC PITMAN & SONS (CANADA), Ltd. (INCORPORATING THE COMMERCIAL TEXT BOOK COMPANY) PITMAN HOUSE, 381-383 CHURCH STREET, TORONTO MADE IN GREAT BRITAIN AT THE PITMAN PRESS, BATH El—(T.575) To all those ivho have contributed to the art of Television and in so doing have made possible the uniting of this book PREFACE Several years have passed since standards for high-definition cathode-ray television transmission were set up in this country and in the U.S.A., and although the war years have retarded progress, at least in a direct sense, the soundness of these standards has been proved by the satisfactory performance of normal commercial receivers. In view of the decision taken in both countries to resume transmissions on the pre-war standards, and of the prevailing economic situation, it seems unlikely that radical changes will be made in the transmission standards for some considerable time. It is felt, therefore, that television technique may be regarded as stabilized to an extent that justifies a systematic treatment of its basic principles, particularly in regard to reception, since receiving equipment is more likely to conform to a general pattern than transmitting equipment. The urgent demand, by the engineers of a receiver manufac­ turer’s servicing organization, for a lucid, descriptive treatment of reception principles (as distinct from the existing literature, which deals with television from a more specialized, advanced, or comprehensive point of view) was responsible for the produc­ tion of this book in its original form—as a short correspondence course. With the present increase of interest in, and production of, television equipment, it is felt that the book may be of service to a wider field. Accordingly, an attempt has been made to describe in clear, direct, and accurate terms, the principles underlying the technique of television reception. The treatment is qualitative and entirely non-mathematical, such mathematical aspects as are of fundamental importance being relegated to an appendix ; it is, however, largely theoretical in that it does not deal primarily with practical details of design or servicing. Since interest is centred on principles it is logical to have dealt to some extent with American technique, and it is hoped that vii viii PREFACE the selection of examples of circuit design for both standards will provide a better understanding of the art generally without leading to confusion. The book may be divided into four parts, as follows— (i) A general outline of the complete television process (Chapter I) as standardized here and in the U.S.A., for mono­ chromatic reproduction ; this brings out the more advanced nature of television technique by comparison with ordinary sound broadcasting and justifies the reinterpretation and exten­ sion of basic signal and circuit theory given in Chapter II. (ii) Stage-by-stage examination of the complete receiver working in conformity with established design and servicing pro­ cedure, from the picture tube and its auxiliaries (Chapter III) through the scanning (Chapter IV), synchronizing (Chapter V), and signal (Chapter VI) circuits to the vision receiver input. These chapters are followed by a review of methods of receiving the sound signal (Chapter VII) and in the succeeding chapter (VIII) several complete circuit schematics of com­ mercial receivers in current use are described in order to coordinate details given in the preceding chapters. (iii) A description of the receiver accessories, namely the aerial system (Chapter IX) and test equipment (Chapter X). (iv) A review of the problem of television transmission in natural colour, followed by an account of the two basic methods demonstrated to date. Each chapter includes a selection of suitable references which, together with the general guidance presented in Ap­ pendix II, introduce the reader to the general literature and facilitate further study. Particular care has been taken with terminology; the British usage has been preferred where variation exists and a list of equivalent terms has been provided for the benefit of American readers. (See p. xv.) In view of the modern preference for the terms “resistor” and “capacitor” I have felt it desirable to adopt “inductor” and reserve “coil” for actual windings only. Since a practical “coil” may in fact consist of several windings on a built-up PREFACE ix magnetic core and enclosed in a screen such a distinction would appear to be justified, and while this decision may be question­ able in the case of scanning and focusing “coils.” it has the merit of allowing consistent use of resistor, capacitor, and inductor, which practice is becoming more general both here and in the U.S.A. The book is published by kind permission of my former employers, R.F. Equipment, Ltd., of Langley Park, Bucks. 1 am fortunate in having worked under such pioneers as Messrs. O. S. Puckle and W. H. Stevens and am deeply grateful to the many members of the television and service departments of Sobell Industries, Ltd., who co-operated in producing the original MS. In rewriting and expanding the latter I have been fortunate in obtaining a great deal of information from commercial firms in this country and in the U.S.A.; these organizations are listed on p. x. I am grateful to Mr. D. Clatworthy for assistance with the drawings. I would be glad to receive (through the publishers) notice of errors and suggestions for improving the text. In conclusion I would like to acknowledge the tremendous amount of help and encouragement from my wife Barbara, but for whom the book could not have been written. A. W. KEEN Harrow December, 1947 A C K N O W LEDGM E N T S The following organizations have supplied information, as acknowledged in the text, and the author is grateful for the co-operation extended by their representatives— Belling & Lee, Ltd. British Broadcasting Corporation Cathodeon, Ltd. Cossor, Ltd. Edison Swan Electric Co., Ltd. E. K. Cole, Ltd. (“Ekco”) Electrical and Musical Industries (E.M.T.), Ltd. Electrical and Radio Trading Electronic Engineering Endeavour (I.C.I., Ltd.) General Electric Co., (U.S.A.) Haynes Radio, Ltd. Institute of Radio Engineers (U.S.A.) Marconi Instruments, Ltd. Murphy Radio, Ltd. Pliilco Corporation (U.S.A.) Pye, Ltd. Radio Corporation of America R.F. Equipment, Ltd. Sobell Industries, Ltd. The Gramophone Co. (H.M.V.) Westinghouse Electric Corp. (U.S.A.) Wireless and Electrical Trader Wireless World X C O N T E N T S PAGE Preface ........ Vii Table of Equivalent British and American Terms. XV CHAPTER I An Outline of the Television Process 1.1 The present position of television 1 1.2 The problem of picture transmission 2 1.3 The action of the electronic camera 3 I I The scanning process .... 9 1.5 The video-frequency signal . 12 1.6 Reconstruction of the picture at the receiver I I 1.7 Synchronizing the transmitter and receiver 16 1.8 The composite video signal Hi 1.9 D.C. modulation : brightness level 20 1.10. The complete television system . 23 1.11. The sound channel .... 26 1.12. Present frequency assignments 27 1.13. Summary of recent developments 27 Bibliography ... 28 CHAPTER II Basic Signal and Circuit Theory 2.1. Graphical representation of voltage and current variations ...... 30 2.2. Analysis of complex waveforms .... 33 2.3. Transient response of simple networks . 36 2.4. Simple wave-shaping networks .... 43 2.5. D.C. restoration. ..... 48 2.6. General features of special valve circuits in television receivers ...... 51 2.7. Basic valve circuit arrangements 53 2.8. The cathode input (“grounded-grid”) amplifier 53 2.9. The cathode-output (“cathode-follower”) amplifier 56 2.10. The “ bootstrap ” circuit . 58 2.11. Comparison of the three basic valve arrangements 58 2.12. The cathode-coupled double-triode amplifier. 59 Bibliography ...... 60 xi xii CONTENTS CHAPTER III The Picture Tube and its Auxiliary Circuits PAGE 3.1. Laws of electron motion in electric and magnetic fields 62 3.2. Functional description of the picture tube 66 3.3. The gun : prefocusing and intensity control . 71 3.4. The main focusing system : theory of focusing 72 3.5. The main focusing system: practical arrangements 75 3.6. The deflection system.