Patent GB-287643-A (GB)
Title: Improvements in and relating to television and telephotography
IPC: H04N3/10
Filed: 1926-12-24
Abstract: 287,643. Rtcheouloff, B. Dec. 24, 1926. Television apparatus.-A picture is scanned at the transmitter and retraced at the receiver of a television apparatus by surface-elements carried by the ends of springs which are adapted to vibrate in two dimensions and mounted inside vacuum tubes. Transmitter. An image i1 of the object i, Fig. 1, is projected by a lens j so as to be formed inside a photoelectric cell c. A surface-element g of photoelectric material is mounted on the end of a compound spring composed of two flat pieces a, b, (partly hidden by the pole-piece z, Fig. 1), the ends of which are inserted into perpendicular slots in a ball A, so that the end g can vibrate in two dimensions under the influence of electromagnets d, e. The photo-electric point g is connected through the spring ab, conductor f, amplifier p, and battery k to the anode l, which may be rectangular or may consist of a mesh-work disc (Fig. 2, not shown), or a ring of semicircular cross-section, Fig. 3. The photo-electric current varies according to the brightness of that element in the image i with which the point g coincides at a given instant. The point g may be shielded by a diaphragm v, Fig. 4, having an aperture v1 through which the light can pass. The shield v may be insulated from the element g and may serve as the anode of the cell. In a modification the photo-electric point g may be replaced by a concave or convex mirror which projects light on to a photo-electric layer on the inner wall of the tube c, the end of which is suitably shaped (Figs. 5, 6, not shown). The surface of the convex or concave diaphragm v may be photo-electric or reflecting if desired. According to the Provisional Specification the photo-electric element g may be replaced by a small spark gap. Receiver. The receiver similarly comprises a compound spring a1, b1, carrying a surface element g1 of fluorescent material which is caused to vibrate in two dimensions by the magnets d1, e1. The spring a1, b1 functions as anode to a filament q which is fed by a filament battery q1 and surrounded by a negatively charged reflector t. A corresponding grid s is energized by potential controlled over the line 1, 2, by the output of the photo-electric cell c at the transmitting station. The energy of the cathode stream impinging on the element g1 is therefore varied in accordance with the brightness of the elements of the picture i at the transmitting station, and the intensity of fluorescence of the element varies accordingly. The picture traced by the element g1 is projected by a lens D on to a screen B outside the vacuum tube c1. In a modification the fluorescent element g1 may be replaced by a small spark gap. Synchronous control of scanning point and retracing point. The springs a, band a1, b1 carrying the scanning and retracing elements g, g1, respectively, are vibrated by magnets d, e, d1, e1, under the control of alternating or intermittent currents passing from generators m, n, over lines 3, 4, 5, the frequencies of the two currents being in the ratio of 100 : 1 and equal to the natural frequencies of the springs a, a1, and b, b1, respectively. The circuits of the magnets d, e, may be separate, as shown, or may be tuned secondary circuits coupled to a single primary circuit in which the frequencies of the two generators m, n, are superimposed (Fig. 8, not shown); or a single core DE, Fig. 7, having polepieces at right-angles to one another may be energized at the two superimposed frequencies, each part a, b, of the spring responding to the current of its own frequency; or there may be a single pole-piece energized at both frequencies and facing the higher-frequency portion of the spring. Similar arrangements are adopted at the receiving end.