Patent GB-230401-A (GB)
Title: Improvements in electrical transmission of images
IPC: H04N5/40
Filed: 1923-09-07
Abstract: 230,401. Western Electric Co., Ltd., (Western Electric Co., Inc.). Sept. 7, 1923. Television apparatus.-The object, animate or inanimate, of which the image is to be transmitted is scanned by a pencil of light, two series of electrical oscillations of low-frequency, one proportional at each instant to the intensity of the reflected light from the illuminated point on the object and the other to the position of the point, being produced by photo-electric devices and impressed upon a high-frequency carrier wave for transmission. At the receiving station the two series of low-frequency oscillations are filtered out, the first-mentioned, which is, in general, of greater frequency than the latter, being utilized to control the potential of the grid of a Braun tube and thus to control the intensity of the cathode-ray stream which illuminates a screen. This ray stream is moved over the screen synchronously with the scanning of the object, by electromagnetic or electrostatic action produced by the low-frequency oscillation, which is proportional to the position of the scanned point of the object, to produce the image. Fig. 1 illustrates diagrammatically the apparatus at the transmitting station; Fig. 2 shows the relative positions of object, scanning mirror, and and photo-electric cells. The object is scanned by a mirror 15 oscillated in the manner and bv the means described in Specification 228,961. Light is reflected by the mirror 15 as it scans the object 16 on to a lens 21 which distributes it over the cathode of a photo-electric cell 17. The resultant oscillatory currents set up in the cell 17 by the battery 20 are amplified by amplifiers 23, 29 and modulate, through a modulator 35, a carrier wave of high frequency generated by a generator 38. This carrier wave is further modulated through the same modulator 35 by low frequency oscillations proportional to the positions of the points on the object, and generated by the photo-electric device 51. Light from a constant source 45 is reflected by the mirror 15 as it scans the object on to the light sensitive cathode 50 of the vacuum device 51. Current passing from the cathode 50 to one or both of the anodes 53, 54 is dependent, owing to the presence of an auxiliary electrode 56 carrying a fixed charge, on the radial distance at which the incident ray strikes the cathode and this will be a function of the position of the point on the object being scanned by the mirror. The object may, if necessary, be illuminated by steady light or intermittent light of high-frequency. At the receiving station the two low frequency oscillations are detected by the detector 167, Fig. 3, the oscillation which is proportional to the intensity of light being filtered out and, after amplification by amplifiers 199, 202, is applied to the grid 160 of a Braun tube 140. The other oscillation is filtered out, and, after amplification by an amplifier 175, is applied, through a transformer 177, to a circuit containing the parallel plates 156 of a condenser and, also, through an inductive coupling at 180, to a circuit containing the parallel plates 157 of another condenser having its plates at right angles to the plates 156. The result is that the concentrated beam of light rays in the tube 140 is moved over the translucent screen 148 synchronously with the scanning of the object by the mirror to produce the image on the screen.