GB515427A - Improvements in or relating to television and like systems - Google Patents

Abstract

515,427. Television. FAUDELL, C. L. May 31, 1938, No. 16195. [Classes 40 (iii) and 40 (v)] A circuit for the amplitude separation of picture and synchronizing signals comprises an impedance effectively shunted by a unilateral conducting device biassed to be non-conducting during synchronizing pulse periods and so arranged that picture signals are substantially eliminated from the voltage set up across the impedance, which voltage controls a scanning generator. An impedance 4, Fig. 1, in the anode circuit of the valve 2, is shunted by a diode 12. When a picture signal is applied in a positive sense to the grid 1, the diode 12 is conducting, thus shorting impedance 4 so that the anode impedance is effectively impedance 3, the amplified picture signals being taken from terminal 5. When a synchronizing pulse is fed in a negative sense, the diode 12 is non-conducting, the effective anode impedance then being that of impedances 3 and 4 in series. Amplified synchronizing pulses are fed to the valve 7 which is biassed by its grid current to only conduct during synchronizing pulse periods, this having the effect of improving their shape. The frame pulses are taken from across condenser 14 and the line pulses from winding 15 which may be wound on the transformer of the blocking oscillator and is connected to the screen of valve 7. The effects of interference may be eliminated by connecting the anode of an additional diode to the cathode of diode 12 and suitably biassing its cathode, or by the grid current of valve 7 if the amplitude of the pulses applied to this valve are sufficiently great. If synchronizing signals are applied in a positive sense to the grid 1, it is necessary to reverse the connections of the diode 12. In a second embodiment, Fig. 2, a self-establishing D.C. amplifier of the type described in Specification 422,906 is used. Synchronizing signals are applied to the grid of pentode 16 in a positive sense. The anode of the diode 18; which is effectively in shunt with impedance 17, is connected to the anode of pentode 16 so that diode 18 is non-conducting when a synchronizing signal is applied. The voltage drop occurring at terminal 24 is applied to the line and frame deflecting circuits along leads 25, 26, these pulses being separated by circuits 30, 31. On reception of a picture signal diode 18 is conducting and no potential is applied to leads 25, 26. In further embodiments a gas discharge tube may be used as the unilateral conducting device.