Patent GB-255057-A (GB)
Title: Improvements in or relating to television systems
IPC: H04N11/00
Filed: 1926-07-03
Abstract: 255,057. Westinghouse Electric & Manufacturing Co., (Assignees of Zworykin, V. K.). July 13, 1925, [Convention date]. Television apparatus. - The image to be transmitted is projected through a mosaic colour screen on to a photoelectric element, and the image is reproduced at the receiving station through a similar screen disposed between the light producing the image and the observer. Transmitting-arrangements, Fig. 1. The image is projected by a lens 41 through the colour screen 40 and is focussed by a lens 39 on a photoelectric surface layer 48 of a plate 33 forming a partition within a cathoderay tube 27 filled with argon or like inert gas at low pressure. The mosaic of the screen 40 may be composed of small red, blue, and green squares. The plate 33 may be of thin aluminium foil or a. fine mesh metallic screen 35 coated with an insulating layer 36, e.g. of alumina or magnesia, this in turn being coated with the layer 48 of photo-electric material such as potassium hydride. To obtain a suitable colloidal deposit for this purpose, potassium is distilled on to the layer 36, the deposition being stopped before the colour changes from grey to silver, hydrogen is introduced into the tube and a current is passed until the light blue colour of the potassium hydroxide begins to turn to violet. The screen 35 and a grid 37 in front of it are connected respectively to the filament and the grid of an amplifying valve nected through a transformer 11 to the filament grid circuits of modulator valves 7, 8 supplied from an oscillator valve 9. The plate circuits of the valves 7, 8 are connected through a transformer 6, an amplifying valve 5, and a transformer 4 to an antenna, system 3, 1 tuned to oscillate at two separate frequencies. The ray passes from the heated cathode 30 through the tabular anode 32, to which a high potential is applied from an a.-c. source 44 through a rectifier 43. and the ray is caused to explore the screen 35 rapidly under the control of spaced plates 25, 26 inside, and coils 28, 20 outside the tube 27, the coils producing an electromagnetic field parallel to the electrostatic field produced by the plates. The plates 25, 26 are connected through a transformer 24 to the circuit of an alternator or valve oscillator 22 producing current at e.g. 1000 cycles, and the coils 28, 29 are similarly connected to the circuit of an alternator or oscillator 23 producing current at e.g. 16 cycles. The alternator circuits are connected through transformers 20, 21 to the filament grid circuits of modulator valves 16, 17 supplied from an oscillator valve 18, and the plate circuits of the valves 16, 17 are connected through a transformer 15, an amplifying valve 14, and a transformer 13 to the antenna system 3, 1. The current in the input circuit of the valve 12, dependent on the electron emission from the layer 48, is thus controlled by the light intensities and by the colours of the elemental areas of the image being transmitted. Receiving-arrangements, Fig. 2. The modulated oscillations from the valves 9 and 18 are received by an antenna system 51, 50 resonant to both frequencies. Those from the valve 9 are transferred through a transformer 52 to a detector valve 53 of which the plate circuit includes the heated cathode 56 and the grid 54 of an argon-filled cathode-ray tube 55. Those from the valve 18 are transferred through a transformer 67 to a circuit 68 including the primary windings of transformers 69, 70 which separate the modulated oscillations due to the alternators 22, 23 respectively by valves 71, 72 of which the plate circuits are transformer-coupled to the circuits of plates 58, 59 and coils 73, 74 corresponding to the plates 25, 26, and coils 28, 29, Fig. 1. The cathode ray passes through the tubular anode 57 to which a high potential is applied from an a.-c. source 66 through a rectifier 65, and the ray explores rapidly a fluorescent screen 60 within the tube, this exploration being synchronous with that of the screen 35 at the transmitter. The image produced is projected by a lens 61 through a mosaic screen 64, similar to the screen 40, Fig. 1, and with the colour squares in corresponding positions, on to a ground glass screen 63. The fluorescent material on the screen 60 mav be a mixture of caesium chloride, calcium tungstate, zinc sulphide, and zinc silicate which emit respectively red, blue, greenish yellow, and yellow light.