GB604759A - Improvements in or relating to television systems and receivers - Google Patents

Abstract

604,759. Television. PHILCO RADIO & TELEVISION CORPORATION. March 16, 1945, No. 6676. Convention date, May 30, 1944. [Class 40 (iii)] [Also in Group XL (c)] In a television transmission system the picture signals and vertical synchronising signals are transmitted as amplitude modulations of one carrier wave, and sound signals and horizontal synchronising signals are transmitted as frequency and amplitude modulations respectively of a second carrier wave. The arrangement obviates the difficulties introduced in a television system, when large amplitude synchronising pulses are used to overcome interference. The first carrier wave, Fig. 2a, is amplitude modulated by picture signals 17, 18, horizontal blanking signals 19 and vertical synchronising and blanking signals 24, 25. The second carrier wave, Fig. 2b, which is frequency modulated by the concomitant sound transmission, is amplitude modulated by the horizontal synchronising signals 43, which, as shown, are made to coincide with the leading edges of the blanking signals 19, but which, if desired, may be arranged to occur slightly before the blanking pulses, whereby, in either case, a saving in fly-back time may be effected. Moreover, since no pedestal is required for the synchronising signals, the pulses 19 may be omitted and the carrier reduced to zero during such intervals and reintroduced at the receiver. The receiver comprises a common frequency changer which converts the two carriers to different intermediate frequencies. The sound signals are separated from the synchronising signals, carried by the same intermediate frequency, by a limiter, or, alternatively, after discrimination, by an audio-frequency filter. To obtain the horizontal synchronising signals, the intermediate frequency signal is rectified by a diode detector circuit which is so designed that any small amplitude modulation, corresponding to the frequency modulation, is eliminated. Specifications 398,512, 514,643 and 562,707 are referred to.