Patent GB-271131-A (GB)
Title: Improvements in television and like apparatus
IPC: H04N3/04
Filed: 1926-02-09
Abstract: 271,131. Clay, R. S. Feb. 9, 1926. Television; copying-telegraphs.-In receiving apparatus employing a moving pencil of cathode rays for reconstituting the picture on a fluorescent screen for television or on a photographic surface for producing a permanent record, the intensity of the pencil entering the traversing field is varied without variation of the direction or velocity of its entry by subjecting it to a preliminary deflection proportional, directly or inversely, to the light intensities to be reproduced or recorded. Transmitting arrangements. An image of the picture or scene produced by lens 1, Fig. 1, in the plane of a mask 4 is traversed by radial slots 7, 8, Fig. 2, in overlapping discs 2, 3 respectively rotating at relative speeds of e.g. 100 to 1 immediately behind an aperture 6 in the mask. The whole image is thus rapidly and repeatedly traversed by the light which passes through the aperture 10 where the two operative slots cross. and this light is incident on a photo-electric cell 5. The discs 2, 3 are preferably of sheet steel stretched over the rim of a steel wheel, and may be mounted in a vacuum. Alternatively the exploration of the image may be effected by a spiral series of holes in a single disc, or by a series of holes successively stepped toward one edge of a travelling endless strip. To ensure uniform sensitivity of the cell 5 a lens may be arranged behind the exploration device to distribute the light from all parts of the image on to the same area of the active surface of the cell. Receiving-arrangements. Fig. 6 shows a cathode-ray tube in which the pencil of rays, after a preliminary deflection by a pair of coils or plates 32 energized by the received picture currents, passes through a tube 31 into the traversing field where it is controlled in relation to the reproducing screen 27 by pairs of coils or plates 28, 29 producing alternating fields of different frequencies in directions at right angles. Each of the circuits controlling these fields includes a condenser and either a neon lamp or a resistance to produce quick return in the movement of the pencil. The intensity of the pencil entering the traversing field is thus diminished in accordance with the degree of the preliminary deflection, and the received picture currents must therefore be inversely proportional to the light intensities incident on the transmitting cell 5. The tube 31 is shielded by magnetic material or is made of a good electrical conductor according as an electromagnetic or an electrostatic deflecting field is employed. To enable the pencil to enter the traversing field in a direction parallel to the axis of the tube 31, a second pair of coils or plates 34, deflecting oppositely to the coils or plates 32, may be provided as shown in Fig. 7. In this case the tube 31 may be displaced to the position indicated at 43 to enable received currents to be einployed which are directly instead of inversely proportional to the transmitted light intensities. In a further modification, Fig. 8, the pencil leaving the field of the coil or plates 34 encounters the edge of a screen 37 and its intensity is thus diminished in accordance with the degree of deflection. The edge of the screen may be notched to obtain the desired relation between the degree of deflection and the resultant intensity. The pencil is restored to the axial direction of the tube 31 by two additional pairs of coils or plates 35, 36. The intensity of the pencil may be increased by a solenoid 42, Fig. 6, or by placing a tube 33 around the filament 30. To increase the light intensity on the screen 27 several pencils of cathode-rays may be arranged to converge to a point on the screen, such pencils being subjected simultaneously to the deflecting and traversing fields. Synchronizing the exploring devices at the two stations. The aperture 6, Figs. 1 and 2, in the mask 4 may be so arranged that a dark interval is transmitted after each traversal of the image by one of the slots 7 or by one of the holes in the exploring disc or strip when such is used, and the currents corresponding to this periodic interval are used to control the frequency of an oscillating circuit supplying the coils or plates 29. A similar interval following each complete traversal of the image may be used to control the frequency of the circuit supplying the coils or plates 28. Alternatively, light may be arranged to pass through an aperture in the exploring device, at each of the above intervals, to energize a photo-electric cell to produce the synchronizing impulses.