GB452369A - Improvements in methods of and apparatus for picture transmission - Google Patents

Abstract

452,369. Television transmitters. LIPPINCOTT, D. K., 57, Post Street, San Francisco, U.S.A. Feb. 15, 1935, No. 4978. [Classes 39 (i) and 40 (iii)] Scanning is performed by alternately disclosing and occulting complete successive lines across the picture to be transmitted, the disclosing and occulting of each line taking place in the direction of the line. An elon. gated aperture 7, Fig 8, is traversed in the direction of its length across the picture 4( to gradually disclose a complete line so that the signal produced corresponds to the curve 45 and at any point is proportional to the total light in the portion of the line disclosed. This signal is then differentiated (as by passing it through a transformer) to obtain the signal 46 which corresponds to a scanning performed with an infinitely small aperture. The method avoids aperture distortion. As applied to a Farnsworth transmitter, the electron stream corresponding to the picture, is traversed across an elongated aperture 7 Fig. 1, co-operating with an elongated anode 9, and the secondary electrons emitted by the anode are drawn to the shield 6 to produce a current flow through a resistance 14 and inductance 12. Valves 20, 21 have their inputs connected to the inductance 12 and resistance 14 respectively, and their outputs connected in parallel to the resistance 32. The inductance 12 produces the differential of the signal current, while the resistance 14 and valve 21 compensate the voltage drop across the inductance 12 due to its inherent resistance, so that the output across the resistance 32 is the first differential of the current applied to the inductance 12. The return strokes of the aperture are performed quickly and produce a signal across the inductance 32 of opposite sign to the picture signal and this signal is used as a synchronizing signal. At the receiver, the cathode ray tube is biassed so that these signals cut off the ray. The end of the elongated aperture may be square, Fig. 6 (not shown), or curved to produce a signal simulating a cut-off at some given frequency, Figs. 4, 5. As applied to disc scanning, a disc 75, Fig. 9, has elongated apertures 76 adapted to trace adjacent lines on the picture to be transmitted, and a shutter disc 81 cuts off each aperture when it has completely disclosed one line. There are no return strokes to generate synchronizing impulses in this embodiment.