GB426672A - Improvements in and relating to television systems - Google Patents

Abstract

426,672. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.- (Assignees of Ogloblinsky, G. N.; 22, Merrick Villa, Collingswood, New Jersey, U.S.A.) Jan. 3, 1934, No. 259. Convention date, Jan. 3, 1933. [Classes 39 (i) and 40 (iii)] In a television transmitter of the cathode-ray type, the intensity of the cathode ray is varied to yield carrier frequency, synchronizing signals, and control of the average brightness of the picture. An image of a film or other object 20 is formed on a mosaic photo-electric screen 12 which is scanned by the cathode stream 16. The current-strength of the cathode stream is varied at carrier frequency by connecting the oscillator 44 to the control grid 18, and the modulated carrier is transmitted through apparatus 42. The control grid 18 is also supplied with synchronizing impulses which are generated at line-scanning and at framescanning frequencies by the generator 30 and are amplified at 50 so that the carrier conveys both picture signals and synchronizing-signals. The same impulse - generator 30 feeds two generators 26, 28, which produce currents of saw-tooth wave-form at line-scanning and frame-scanning frequencies for the scanning- coils 22, 24 respectively. The energy-level of the signals is controlled in accordance with the average brightness of the pictures by a photocell 56 which is illuminated through the film by a light-source 54 and feeds the control grid 18 through a D.C. amplifier 58. When an outdoor view is to be transmitted an image of it is formed on the photocell 56, Fig. 5, (not shown). In a modification, Fig. 6, (not shown), the photocell 56 is not used, but a portion of the energy outgoing from the wireless apparatus 42 is fed back to the grid 18 in such manner as to control the intensity-level of the signals.