GB525629A - Improvements in or relating to television systems - Google Patents

Abstract

525,629. Automatic volume control; television. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. Feb. 24, 1939, No. 6124. Convention date, Feb. 25, 1938. [Classes 40 (iii) and 40 (v)] Gain control in a television receiver is effected by first bringing the average picture brightness to a substantially constant value and then bringing a datum level to a substantially constant value. The Figure shows the picture amplifier divided into sections V1, V2 and having initial gain controlling means R1 effective upon the first stage to render the average value of the picture signals substantially constant. Further gain control means R2 is responsive to departure from the average value of the amplitude level, representing a fixed datum level, and is effective upon the amplifier V2 and synchronized from the deflecting waveform generator A. In a modification, Fig. 3 (not shown) the output of the section V1 is amplified in the section V2 before application to the generator A. Instead of dividing the picture signal amplifier into sections a single amplifier may be used with gain controlling means to render the average value of the picture signal constant and a further gain control means responsive to departures from the average level effective on the first gain control means, Fig. 5 (not shown). The Specification discusses the time constant of the control networks and the arrangements necessary to avoid overloading. Specifications 458,585 and 489,275 are referred to.