Improvements in and relating to television apparatus

• Main Author: GERMANY LESLIE WALTER
• Format: Patent
• Language: English
• Published: 07.10.1953
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; PICTORIAL COMMUNICATION, e.g. TELEVISION; TRANSMISSION

697,966. Television. PYE, Ltd. July 11, 1951 [July 11, 1950], No. 17361/50. Class 40 (iii). A circuit arrangement for eliminating lowfrequency interference on a television waveform comprises a circuit which produces an output corresponding to any low-frequency interference present and means for combining the output subtractively with the original television waveform. Positive-going television video signals are applied to the control grid of valve V1, the output circuit of which comprises a diode V2 and condenser-resistor network C, R. Lowfrequency interference producing a variation in the peak level of the line-synchronizing pulses will result in a corresponding signal being produced across the condenser C, this signal being applied to the control grid of valve V3. The television video signal is also applied to the control grid of valve V4 which has a common anode circuit with V3. The signal appearing in the common anode circuit consequently comprises the interference signal combined in antiphase with the video waveform whereby the interference present originally in the video waveform is substantially eliminated. This signal is satisfactory for use at a transmitter for application to a monitor; however, an improved signal is obtained for transmission by application of the signal to a valve V5 including a delay-line circuit connected to its anode to derive line-synchronizing pulses which are applied to pulse-shaper V6 and phase splitter V7, the latter delivering a pair of oppositely phased pulses which are applied respectively to the oppositely-poled diodes V9A, V9B, providing a diode-clamp circuit. The video waveform is applied to the control grid of valve V8, and lowfrequency interference is eliminated therefrom in the anode circuit of valve V8 by means of the action of the diode clamp.