GB859081A - Improvements in or relating to colour television transmitting systems - Google Patents

Abstract

859,081. Colour television. ELECTRIC & MUSICAL INDUSTRIES Ltd. April 25, 1957 [April 25, 1956], No. 12635/56. Class 40(3). In a colour television transmitting system, such as the American N.T.S.C. system, wherein the image information is transmitted by means of a brightness signal and a chrominance signal, the frequency components of which are arranged to be interlaced, e.g. by employing a chrominance sub-carrier of frequency equal to an odd integral multiple of half line frequency, the brightness signal is filtered before interlacing is effected in order to remove or attenuate undesired signals, such as noise, from the frequency gaps into which the respective components of the chrominance signal are to be injected. The invention prevents the undesired signals from producing colour interference in a reproduced image. The filtering is effected by a multiple bandpass filter having pass bands centred at harmonics of line frequency and stop bands centred at odd multiples of half line frequency. Reference is made to the use of a filter based on ultra-sonic delay lines. By passing the brightness signal through two channels in parallel, only one of which includes such a filter, and furthermore by controlling the gain of the channels in accordance with the amplitude of the chrominance signal, that which includes the filter directly and the other inversely, it may be arranged that the filtering becomes inoperative when there is no chrominance transmission.