GB514509A - Improvements in or relating to synchronising impulse separator circuits for use in television receivers - Google Patents

Abstract

514,509. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and FEWINGS, D. J. March 4, 1938, No. 6894. [Class 40 (iii)] The voltage across an electronic-discharge tube B, which operates on a sharply curved part of its anode-current anode-voltage curve to separate applied synchronising signals from video signals, is rendered constant despite slow variations in the video signals. The mixed signals are fed to a video amplifying valve A with a resistance C between its anode and a source of potential H.T.+, and the rectifier B in series with a resistance D, R is so connected across a portion CP of the resistance C that the anode current in the resistance C biasses back the rectifier. When the rectifier passes current at the synchronising signals, they are fed to an output SP. A choke K is in series between the resistance D and the anode of the amplifier A and between the portions D, R of the resistance there is the primary of a transformer M, the secondary of which is connected to the grid of a valve G with its anode coupled to the anode of the rectifier so that the valve applies reversed video signals to the rectifier at such strength as to cancel unreversed signals reaching the anode through the choke K and resistance D, R. According to modifications : the valve G is resistance-capacity coupled to the point N, Fig. 4 (not shown); the valve G is omitted, and the reversed signals are fed from the secondary of a step-up transformer, Fig. 6 (not shown); no reversed signals are fed to the anode of the rectifier, the choke K is omitted, and a bye-pass condenser for video signals is connected between the point N and the cathode of the amplifier A, Fig. 3 (not shown).