GB797343A - Improvements in or relating to colour television systems - Google Patents

Abstract

797,343. Television. GENERAL ELECTRIC CO., Ltd., BIGGS, A. J., BLIGH, N. R., and BRIDGES, D. H. May 19, 1955 [Feb. 19, 1954], No. 5008/54. Class 40 (3) A compatible colour television system comprises means for generating, separately, a relatively high definition monochrome signal and a relatively low definition frame or line sequential colour signal (representative of the .same subject) which are transmitted simultaneously in such manner that the signals may be separately derived without mutual interference. In the arrangement shown, the high definition monochrome signal, consisting of doubly interlaced frames of 202 ¢ lines with a repetition frequency of 50 frames per second, is generated by a first television camera 1 (Fig. 1), and after modulation in 5 on to a carrier wave of a first frequency from oscillator 7 is supplied via a restigial sideband filter 9 to a transmitting aerial 11. The low definition colour signal consisting of doubly interlaced. frames of 67¢ lines with a repetition frequency of 150 frames per second, the frames being, cyclically, representative of the Red, Green and Blue aspects of the subject and the total bandwidth of which is limited to 1 mc/s. is generated by a second television camera 2 and co-operating three colour filter disc 3 and after modulation in 6 on to a carrier wave of a second frequency from oscillator 8 is supplied via a restigial side-band filter 10 to aerial 11. The frequencies of the two carrier waves may be such that the two signals occupy separate frequency bands or, the colour signal may be modulated on to a sub-carrier wave, the frequency of which is an odd multiple of half the line repetition frequency (which is the same for both signals) and which is modulated on to a main carrier wave together with the monochrome signal. At a colour receiver (Fig. 2), filters 15 and 16 separate the colour and monochrome signals respectively, the former signals being employed to reproduce colour images via picture tube 22 and colour filter disc 23, and the latter signals, frequencies below 1 mc/s. in which are removed by means of a H.P. filter 25, employed to reproduce monochrome images of high definition via picture tube 27. The two images are then combined optically on a viewing screen 28, extreme accuracy of registration being unnecessary owing to the low definition of the colour. Also, owing to this low definition, the camera 2 and the picture tube 22 may have comparatively coarse resolution. For monochrome reproduction a conventional monochrome receiver may be employed. With suitable modification the invention may be applied to cases where the colour signal is line sequential instead of frame sequential.