GB446432A - Improvements in the separation of synchronising signals in television receivers - Google Patents

Abstract

446,432. Television. WILLANS, P. W., and BAIRD TELEVISION, Ltd., 58, Victoria Street, Westminster. Nov. 2, 1934, No. 31553. [Class 40 (iii)] Synchronizing signals are separatedfrom picture signals by an amplitude filter comprising a thermionic valve 1 with an anode 7 receiving electrons directly from the cathode. The incoming high-frequency signals are detected by an auxiliary anode 2, and the detected signals are applied to the controlling grid of the double-diode-triode 1. During the picture signals the mean current to the main anode of the valve, in passing through a resistance 6, makes the potential of the anode 7 zero or slightly negative relatively to the cathode, and no space current flows to it. During the synchronizing signals, which are produced as described in Specification 436,108, the current to the main anode falls, and space current passes to the anode 7, and is used to control a time-base circuit through a transformer 8. According to modifications; the resistance 4 is replaced by a battery giving such a bias that the valve acts as an anodebend detector, Fig. 2 (not shown); the valve is biassed by a resistance carrying the main anode current, Fig. 3 (not shown); if the modulated carrier varies in strength or the level of the synchronizing signals varies, the anode 7 is connected to the positive potential through an impedance and a resistance, and the junction of the impedance and resistance is connected to earth through a condenser, Fig. 4 (not shown).