Multi-Channel Television

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    ONE of the difficulties met in designing a new system of television is the narrowness of the frequency band of the waves permissible when only one channel of transmission is used. At the Institution of Electrical Engineers on Jan. 6, C. O. Browne showed how this difficulty can be largely overcome by using a number of transmission channels. By using five channels, the frequency band is increased five times and the difficulties of design are greatly diminished. In addition, the velocity with which the scanning spots travel over the surface of the picture is decreased and the difficulties of good synchronisation are largely obviated. To get a moderately good picture, experience shows that the picture should consist of 15,000 picture points at least, and the picture must be scanned about 12½ times per second. This number was chosen because the standard frequency of the supply mains in Great Britain is 50. With small screens, satisfactory results are obtained, but when a ground glass screen measuring 24 in. x 16 in. is used there is a decrease in the brilliance of the received image. With the large received picture, the effect of flicker is pronounced and a higher scanning speed than 12½ pictures per second needs to be used. The author has investigated the best conditions for operating the Kerr cells used in the receiver, and discusses the effects produced by geometric, nonlinear, and frequency distortion.

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    Multi-Channel Television. Nature 129, 124 (1932) doi:10.1038/129124c0

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