Patent GB-694005-A (GB)
Title: Improvements in or relating to apparatus for effecting transmissions of television images
IPC: H04N7/01
Filed: 1951-06-05
Abstract: 694,005. Television. RADIO-INDUSTRIE. June 5, 1951 [June 6, 1950], No. 13313/51. Class 40 (iii). In a television transmission system comprising one or more relay stations and involving one relay link of narrow band width, means are provided at the input to this link for reproducing successive frames of the transmitted image, storing one frame or a plurality of frames in superposition from each successive group of frames, the groups comprising a predetermined number of successive frames, scanning the stored frame or frames at a rate equal to the frame frequency divided by the number of frames in a group, and transmitting the resultant signal over the narrow-band link. At the receiver means involving scanning each converted frame a plurality of times at the original frame frequency are provided for effectively restoring the original television signal. In the embodiment shown, which is applied to a system transmitting 25 doubleinterlaced pictures per second, the picture signals at the input to the relay link are applied to a cathode-ray tube 11 and reproduce a normal picture on the screen thereof. A photographic film 18 is driven in front of the screen of the tube 11 and remains stationary before the screen for successive periods of <SP>2</SP>/ 25  second, being moved on rapidly in the intervening periods. There are thus produced on the film a succession of records comprising the superposition of two complete pictures (i.e. four interlaced frames). Alternatively a blocking circuit 17 may be employed so that alternate pictures are suppressed, successive records then corresponding to alternate pictures. The film 18 passes through a rapid development process and is then passed before a cathode-ray tube 21 which effects flying-spot scanning of the film at a rate of 12¢ double-interlaced pictures per second, each record remaining in front of the tube 21 for <SP>2</SP>/ 25  second and being scanned once by two interlaced frames. The output signal from the photo-cell 26 is amplified at 28 and transmitted over the relay link to the relay receiver where it is applied to a cathode-ray tube 31 to produce 12¢ double-interlaced pictures per second. Successive pictures are recorded on the film 38 which is rapidly developed and then passed in front of cathode-ray tube 41 where it remains stationary for successive periods of <SP>2</SP>/ 25  second. The scanning raster on tube 41 is of normal form, i.e. it comprises two interlaced frames repeating every 1/ 25  second, and effects flying- spot scanning of successive records on the film 38, each record providing two complete pictures each of two interlaced frames so that the signal delivered from the photo-cell 46 is of the same form as that at the input to the tube 11. In a modification, each third frame is converted into one occupying <SP>3</SP>/ 50  second and is interlaced with the succeeding converted frame. In an alternative embodiment, Fig. 4 (not shown), employing double-ended storage tubes, the transmitter end of the relay link comprises two such tubes upon which alternate <SP>2</SP>/ 25  second portions of the incoming signals are recorded, the recorded signals being picked off from each tube during the intervening <SP>2</SP>/ 25  second periods. The receiver end of the link comprises four doubleended storage tubes grouped in pairs, the incoming signals being recorded on both tubes of alternate pairs in successive <SP>2</SP>/ 25  second periods. During the time that recording is being made upon one pair of tubes, successive outputs, each occupying <SP>1</SP>/ 25  second, are taken from each of the other pair of tubes, the outputs from all four tubes being combined to produce a signal of the same form as the original signal.