GB387536A - Television method - Google Patents

Abstract

387,536. Television ; valve circuits ; cathode-ray tubes ; photo-electric cells. ARDENNE, M. VON, 19, Jungfernstieg, Lichterfelde, Berlin. March 29, 1932, No. 8932. Convention date, March 27, 1931. [Classes 39 (i), 40 (iii), and 40 (v).] In a television system the scanning of the image at the transmitter is effected by means of Braun tubes in combination with a lens, the light transmitted through the fluorescent screen, when a film or diapositive is being transmitted, being passed through the film &c. on to the photo-cell, or the scanning ray, when a definite object or scene is being transmitted, causing the photo-cell to be excited by light reflected from the object &c. According to the arrangement shown in Fig. 1, in which the transmission of a diapositive is being effected, Braun tubes 1, 21 are used both at the transmitter and receiver, and the deflecting potentials applied to the plates 5, 19, 6, 20 are controlled either by line connection to the same oscillating sources 17, 18 or by wireless control, the source 17 determining the line frequency and the source 18 the image frequency. Mains supply apparatus 16, 22 furnish the potentials applied to the anodes 4, 25 and to the Wehnelt cylinders 3, 24, and also control the heating of the cathodes. A mat screen 13 is interposed between the diapositive 12 and photo-cell 14 to diffuse the light reaching the latter, and the photo-currents after amplification at 15 are passed to the Wehnelt cylinder 24 of the receiver tube. When the diapcsitive is of small size, it may be placed close to the fluorescent screen 7 between the latter and the lens 8. For scanning purposes the sources 17, 18 each furnish a " tilting " or quick-return oscillating potential, the frequencies preferably being arranged so that neither the mains frequency nor the line frequency is an exact multiple of the image frequency. Blurring of the received picture at the completion of each image may be prevented by causing the ray to return along one edge of the picture, while, to compensate for uneven lighting, the edge of the image may be shaded. When a film is being transmitted the discharge of the condenser which, as described later, effects the quick-return oscillation of the cathode ray, must take place during the advance of the film, preferably by a rotary contact, associated with the feed mechanism, short-circuiting the condenser. In this case, the return movement of the ray is almost instantaneous and does not affect the received picture. Scanning. In each of the apparatus 17, 18 the oscillatirg potentials are generated by utilizing the saturation current of a twoelectrode valve 37, Fig. 5, to charge uniformly and gradually one' of a series of differentvalued condensers 35, 35a, 35b until its discharge potential is reached, and then discharging through a glow lamp 46. The valve 37 is included in circuit with a rectifying valve 41 and the secondary winding of a transformer 40, while the filament heating is regulated by adjustment of coarse and fine variable resistances 38, 39, the charging and discharging oscillations being applied to the deflecting plates of a Braun tube 47. Cathode-ray tubes. The fluorescent screens are produced by spraying cadmium tungstate into the tubes on to a surface of potassium silicate. In the receiving tube 21, in addition to the Wehnelt cylinder 24 that controls the intensity of the ray, there may be incorporated, an additional electrode 32, Fig. 2, which, by deflecting the ray transversely, regulates the screening effect of the anode 25. Automatically acting means are provided for preventing burning of the fluorescent screen due,to the ray remaining stationary at any' point. Each of the supply apparatus 16, 22 for the tubes may comprise a transformer 51, Fig. 6, adapted through one winding 59 and variable resistance'60 to supply the cathode heating current, and through a second winding 58 to heat the filament of a two-electrode rectifying valve 52, which, in association with a third winding 57 and condenser 53 controls the anode potential, while a resistance 54 determines the biasing potential of the Wehnelt cylinder. Photoelectric cells. When transmitting scenes or objects several coacting cells or a single annular cell may be employed, and these preferably have an argon filling. Valve circuits. The photo-cell 14 is enclosed in a separate casing together with the first amplifying valve V1, which has a small amplification factor to avoid introduction of reaction. The filament lead for the middle section of the amplifier is bridged by a condenser 28, and a decoupling choke 29 is interposed between the final and preceding sections.