Abstract :
Referring particularly to point-to-point links, the paper is concerned with the long-outstanding problems of measuring and specifying the transmission performance of those parts of a television system which can be treated as linear networks. Such problems are more easily studied in terms of waveform responses than of steady-state characteristics, because the permissible distortions of television signals can be expressed more directly in terms of time than of frequency. Studies have been somewhat hampered by the dearth of published information on waveform responses taken under practical everyday conditions. The paper offers assistance by giving typical examples from a series of tests, made by the Post Office with the co-operation of the British Broadcasting Corporation, on some of the links and items of equipment used in the 405-line system. The responses were taken with the aid of a set of sine-squared pulse and other test signals shown by experience to be particularly convenient for the purpose. Two complementary methods of specification are proposed, one for rapid routine-testing purposes, and the other to meet the more precise requirements of acceptance-testing work. Both methods are framed in terms of a ¿rating factor,¿ the value of which can be varied to provide any desired degree of stringency. The acceptance-test method takes advantage of the simplification afforded by the time-series method of expressing waveform responses.
