Patent GB-252696-A (GB)
IPC: H01J31/28
Filed: 1926-05-01
Abstract: 252,696. British Thomson-Houston Co., Ltd., (Assignees of Sabbah, C. A.). May 27, 1925, [Convention date]. Copying - telegraphs; television apparatus.- Relates to transmitting arrangements in which a current varying in accordance with the luminous intensities of successive elemental areas of the picture is obtained by subjecting an opticallyprojected image of the picture to exploration by a cathode ray. In one arrangement, Fig. 1, an image of the picture 17 is projected by a lens 14 upon a thin semi-transparent film 7 of material such as caesium, sodium, or potassium, which reflects the electrons in proportion to the intensity of its illumination. This film is carried by a transparent plate 6 closing the end of a cathode ray tube 1 remote from the heated filament 2. The anode 4 is provided with a central opening through which the ray is directed toward the plate 6, and is connected to the filament through a battery 5. The ray is deflected to explore the image by electric charges imparted to two pairs of spaced plates 18, 19 within the tube, one pair being at right angles to the otner. Exploration in a spiral path, Fig. 3, is obtained by the use of the circuit arrangement shown in Fig. 1. The plates 18 are connected across an inductance 29 and the plates 19 across a resistance 30, and a winding 28 in circuit with the elements 29, 30 is inductivelv connected with the coil of an oscillating circuit 23 - - 26 connected across the grid-plate circuits of two thermionic valves 20, 21. Low frequency current is supplied to the primary of a transformer 22 of which the secondary is connected as shown to the valves to produce in the oscillating circuit a modulated current of the form shown in Fig. 2. A member 8, with pointed electrodes 9 for collecting the reflected electrons, is mounted in the tube 1 in front of the film 7, and is connected to the anode 4 through a resistance 10, and the film 7 is connected to the anode through a battery 12. The current in the resistance 10 is amplified by valves 32, 33 coupled by a transformer 34, and the output circuit is coupled by a transformer 35 to me circuit effecting the line or wireless transmission. The spiral exploration may be replaced by a zigzag exploration by connecting one of the pairs of plates 18, 19 directly to a source of relatively high frequency and the other to one of relatively low frequency. In a modified arrangement, Fig. 5, the plate 6 carrying the film 7 is replaced by a glass plate 42, Fig. 7, backed by fusing on to it a thin layer of a substance such as thallium sulphate or molybdenite of which the resistance varies according to the intensity of the light incident upon it. The polished surface of this layer carries spaced metallic lines 41 electrically connected together and to the battery 12, and the plate 42 carries rows of silver or like metallic plugs 39. In a further modification the ray is incident on the image, projected on the transparent end wall of the tube, through aligned closely-spaced perforations in two parallel metal plates or through two discs of metal gauze connected across the resistance 10. In another arrangement the inner side of the wall is covered with a semi-transparent conducting film e.g. of silver, and the rav is incident on this film through a screen of fine metal gauze and a screen of silk gauze on which the image is formed by the lens 14. The film and the metal gauze are connected across the resistance 10. At the receiving station a similar cathode ray, of which the intensity is controlled by the received currents, is arranged to explore a phosphorescent viewing screen synchronously with the movement of the ray at the transmitting station. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the use of rays corresponding to invisible portions of the spectrum instead of light rays for projecting the original image. This subject-mattter does not appear in the Specification as accepted.