GB595138A - Improvements in television systems - Google Patents

Abstract

595,138. Television transmission systems; multiplex pulse signalling. GENERAL ELECTRIC CO., Ltd., ESPLEY, D. C., and WALTER, D. O. Nov. 6, 1944, No. 21756. [Classes 40 (iii) and 40 (v)] In a television transmission network comprising a carrier link, or a number of carrier links in cascade, and in which the carrier is positively modulated by the picture signals in one or more links, a control signal which is fixed in amplitude and independent of changes in the television signals is superimposed upon, and transmitted with, the television signals and is utilized to control automatically the gain at one or more points in the network. At a terminal station, the control signals are broadcast. The control signals are pulses P preferably exceeding the amplitude of the peak white signals and may be inserted in the synchronizing period S occurring in the blanking signal interval A. The control signals may be inserted at the video-frequency stage by a generator triggered by the leading edges of the synchronizing impulses or they may be inserted at carrier frequency by using a local oscillator operating at that frequency and the oscillations gated to pass to the mixing circuit only during the period of the pulses produced by the generator, or the latter may be employed to control the duration of the oscillations of the local oscillation generator. The pulses may be modulated, provided their amplitude is unaffected, for transmission of information between stations of the link system, for example by phase modulation at different frequencies associated with the various stations. Control of apparatus may be obtained by keying the characteristic frequency to operate a control circuit to produce an operating signal. As a modification, the pulse duration of the control signals may be modulated. The sound accompaniment of the television signals may be transmitted over the link network by modulating the control signals, the sound signals being extracted at the receiver of the terminal station and broadcast from its transmitter on the carrier employed for the picture signals or on a separate carrier. If more than one carrier link is employed, the signals may be transmitted from a repeater station on a frequency different from that on which they were received. Specification 587,498 is referred to.