GB407322A - Improvements in or relating to television transmission systems - Google Patents

Abstract

407,322. Television ; valve amplifying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Konkle, P. J. ; 1601, Sycamore Street, Haddon Heights, New Jersey, U.S.A.) Sept. 8, 1932, No. 25080. Convention date, Sept. 18, 1931. [Classes 40 (iii) and 40 (v).l In a television system in which synchronizing signals of greater amplitude than the peak picture signals are transmitted over the same channel and in which the synchronizing signals are, at the receiver, separated from the picture signals by amplitude selection, the transmitter includes a control arrangement by which the general level of the picture signals is prevented from reaching a value such that the peak picture signals may be of such an amplitude as to cause faulty operation of the synchronizing means at the receiver. In the transmission of a kinema film 12 scanned by a disc 11 associated with a light source 15 and a photo-electric cell 16 to generate the synchronizing impulses. The output from the photo-electric cell 13 generating the picture signals is fed through amplifiers 14, 18 to a wireless transmitter and to an amplifier 25 which controls a valve 26 operating on the lower part of its characteristic. When a light portion of the film is being scanned an increased voltage on the grid of the valve 26 increases its plate current and the grid of a valve 27, operating on the upper portion of its characteristic is made more negative. The reduction in the plate current of the valve 27 reduces the voltage in the circuit of the photoelectric cell 13 with consequent decrease in the output from the cell 13 applied to the amplifier 14. The values of the resistances 28, 29 and capacities 30, 31 are adjusted so that the control arrangement is not responsive to picture signals representing a line or several lines, but only to those constituting at least one picture frame. Specification 398,242 is referred to.