GB443031A - Improvements in or relating to television and like systems, and circuits therefor - Google Patents

Abstract

443,031. Television receivers. LANCE, T. M. C., PUGH, D. W., and BAIRD TELEVISION, Ltd., 58, Victoria Street, Westminster. Aug. 24, 1934, No. 24399. [Class 40 (iii)] In a television or like receiver of the kind in which the synchronizing signals at line and picture frequencies for controlling oscillators associated with the deflecting coils of a cathode-ray tube are separated by a valve circuit including elements, such as a capacity and a choke or transformer, having different impedance-frequency characteristics, the valve or valves are so biassed as to separate the picture signals from the synchronizing signals by grid current rectification, while the synchronizing signals produce negative impulses on the grid. In the arrangement shown in Fig. 1, the valve 1 is fed with picture and synchronizing signals by way of condenser 2, grid resistances 3, 4 and limiting resistance 5, the junction of resistances 3, 4 being connected through high resistance 6 to the positive of the high tension, so that the grid is biassed positively with respect to the cathode. The picture signals tend to increase, and the synchronizing signals to decrease, this bias, so that only the latter appear in the anode circuit, where separation of the two frequencies is effected by condenser 11, resistance 7, and transformer 8. A modification, Fig. 2, employs two valves 12, 18 arranged in parallel and biassed so as to cut out the picture signals, a choke 16 being associated with the anode circuit of valve 12 to pass the lower or picture frequencies via condenser 14 to one oscillator, and a resistance 23 and condenser 22 being associated with the anode circuit of the valve 18 so as to pass the high or line frequencies to the other oscillator. Specifications 320,639, [Class 40 (iii)], and 436,108 are referred to.