GB706182A - Improvements relating to television systems - Google Patents

Abstract

706,182. Television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Aug. 20, 1951 [Aug. 24, 1950], No. 20922/50. Class 40 (3) In a television system for transmitting simultaneously on the same carrier wave picture signals of comparable band width derived from at least two different pictures, the carrier wave is modulated in cyclic order by the picture signals derived from said different pictures, the repetition frequency of said cycles being high compared with the line frequency. Thus signals from two different pictures interspersed with line and frame signals derived from a common generator are sampled alternately so that 200 spaced signals of one programme interspersed with 200 spaced signals of the other programme occur between line synchronizing pulses. The timing of the sampling is changed periodically by 180 degrees to effect interlacing and the Specification describes two sequences for use with normal odd-line interlaced signals to provide interlacing of the samples of one picture produced in one line and staggering of the samples in adjacent lines. Four frames are required to produce a complete picture. Selection of a desired picture at a receiver is effected by a gating device opened at the correct times. In order to change the phase of the gate operation in accordance with the interlacing operation at the transmitter, a special synchronizing pulse may be added to the transmitted signals. Alternatively the change may be controlled by modifying the duration of the line synchronizing pulses. Reference is made to a sampling operation taking place at a large odd multiple of half the line frequency. The two pictures may be those forming a stereoscopic pair. Sound signals associated with the two pictures may also be interspersed with the picture signals. To reduce the cross-talk produced between pictures the gating device operates for only a narrow fraction of the cycle, and any residual cross-talk is reduced by delaying a certain amount of the mixed signals in a high pass filter by a half period of the gating frequency and mixing it with the undelayed signals in suitable phase and amplitude so that the undesired programme components are opposed and reduced.