GB527102A - Systems of transmission for television and the like systems - Google Patents

Abstract

527,102. Modulation systems; television. STANDARD TELEPHONES & CABLES, Ltd. March 31, 1939, No. 10115. Convention date, May 12, 1938. [Classes 40 (iii) and 40 (v)] In a television signal transmission system, the carrier amplitude is varied in accordance with the average level of the signals by means of a control potential obtained by peak rectification of the signals. Carrier from oscillator 3 is supplied in opposite phase to the suppressor grids of valves 1 and 6, and adjustment of resistance 8 and balancing condenser 7 results in elimination of unmodulated carrier in the common anode circuit. Television signals are applied to the grid G11 of valve 1 over condenser 11, and result in the production of modulation sidebands which are transmitted through filter 9 and amplifier 2 to the load circuit 19. A rectifier 13, connected to the output of the sideband filter 9, produces a voltage across resistance 14 dependent upon the peak value of the signals measured in the direction of the synchronizing impulse, and this voltage is fed over a resistance condenser combination 15, 16, of suitable time-constant to the suppressor grid of valve 5. This valve, whose control grid is connected to oscillator 3 over phasing network 18, feeds pure carrier, whose amplitude is controlled by the output of rectifier 13, to the load circuit 19. The phase of the added carrier may be the same as that of the suppressed carrier or may be changed by 180 degrees, in which case the signal will be reversed at the receiving end. In a modification, Fig. 6 (not shown), suitable only for positive television signals, a carrier suppression modulator of the form shown is used, but the peak rectifier is fed with the original signals and the rectified voltage is applied to the control grid of valve 6 to upset the balance and so produce the added carrier current in the load.