GB422914A - Improvements in and relating to television and the like apparatus - Google Patents

Abstract

422,914. Television. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Blyth Road, Hayes, Middlesex, BROWNE, C. O., 29, Monk's Drive, West Acton, London, HARDWICK, J., 66, Drayton Gardens, West Drayton, Middlesex, and BLUMLEIN, A. D., 32, Woodville Road, Ealing, London. July 11, 1933, No. 19691. [Class 40 (iii)] In systems in which the picture signals are mixed with a sub-carrier modulated with e.g. synchronizing impulses, the sub-carrier is prevented from affecting the means for inserting direct current and low-frequency components lost in amplification. The picture signals a, Fig. 3, are interrupted at the end of each line by a signal b of constant amplitude for determining the amount of direct current to be inserted. A synchronizing impulse e, Fig. 5, consisting of a modulated sub-carrier is mixed with the picture signals, giving the resultant oscillatory train of Fig. 6. As applied to a transmitter, the oscillatory train is taken from terminals 5, 8, Fig. 1, and fed to an amplifier 7 whose bias is controlled by the rectifier 10, so compensating for the absence of components incapable of passing the condenser 6. A circuit 9 tuned to the subcarrier frequency prevents rectification of the synchronizing impulses without preventing rectification of the compensating impulses b. As applied to a receiver, a resistance-capacity coupled amplifier 18, 23, Fig. 2, has the bias on the last valve varied to compensate for the absence of components incapable of passing the condensers 16, 22 by the rectifier 37 fed from an amplifier 30, which is fed with the received signals from which the sub-carrier has been removed by the filter circuit 28, 31. This filter is terminated by the grid leak 32 and has a sharper cut-off than the filter of Fig. 1. Specification 422,906 is referred to.