GB252798A - Improvements relating to the radio transmission and reception of pictures - Google Patents

Abstract

252,798. Wright, G. M., and Smith, S. B. March 6, 1925. Copying-telegraphs.-Pictures &c. are transmitted wirelessly by progressively varying the frequency of a transmitted wave in accordance with variations in the light and shade values of elemental areas of the picture. Fig. 1 shows a transmitting arrangement. Light from successive areas of the picture is incident on a photoelectric cell P in circuit with an amplifier A, and the amplified current is applied between the grid and cathode of a frequency modulator valve F. The anode circuit of this valve is coupled at K to part of the oscillatory circuit of a master oscillators M, and potential variations between the grid and cathode of the valve F thus produce corresponding frequency variations in the oscillator M. Such variations are magnified in a transmitter T and radiated as a wave of varying frequency. Fig. 2 shows a receiving arrangement. The receiving aerial N is coupled to an amplifier A' adapted to limit the high frequency currents to the minimum intensity occurring during a fading period so that the output current has substantially the same amplitude for all frequencies. This current is applied through a transformer between the grid and cathode of a valve D of which the anode circuit includes an inductance L of low resistance and of an impedance which is small in relation to the anode-cathode impedance of the valve. The potential. differences across this inductance, which are substantially proportional to the incoming frequencies, are applied to a rectifying valve R, and the output current, after removal of high frequency components by a filter S, is applied to the reproduction of the picture, e.g. by supplying it to a very fine metal filament of a gas-filled lamp acting on a sensitized surface moving synchronously with the picture at the transmitting station.