Patent GB-785728-A (GB)
Title: Improvements in or relating to the magnetic recording and reproduction of televisionsignals
IPC: H04N5/919
Filed: 1955-06-21
Abstract: 785,728. Television. PHILIPS ELECTRICAL INDUSTRIES, Ltd. June 21, 1955 [June 24, 1954], No. 17920/55. Class 40 (3). Television signals are recorded magnetically by a method in which the signals are first converted electro-optically to an image which is then scanned off at a lower standard, i.e. line rate, picture rate or both, to produce signals of a bandwidth within the capabilities of magnetic recording apparatus. Reproduction is effected by an inverse process, the signals read off from the magnetic recording at the lower scanning standard being displayed and the resulting image being scanned to generate signals at the original and higher standard. In its simplest form, Fig. 2 (not shown), the signals to be recorded are merely applied to a cathode-ray tube to reproduce an image conventionally, the scanning standard being say, 50 pictures per second, and the cathode-ray tube is viewed by a pick-up tube operating at a lower scanning rate of, say, 12.5 pictures per second to generate signals having a bandwidth preferably less than 1 Mc/s and suitable for application to the head of a magnetic tape recorder. Reproduction is effected by reversing the functions of the cathode-ray reproducer and pick-up tubes. In another way of carrying out the invention,. Fig. 1, the television signals at V are applied to a cathode-ray tube 1, the resulting image being projected by optical means (not shown) on to four pick-up tubes 3a ... 3d arranged so that each views onequarter of the image. The pick-up tubes operate at the same picture rate as the original signals but at a line-scanning rate of onequarter. The resulting signals pass through amplifiers 6a . . . 6d and are recorded on parallel tracks on magnetic tape 4 by heads 5a ... 5d. In reproduction cathode-ray reproducing tubes are substituted for pick-up tubes 3a ... 3d and a single pick-up tube at 1 views the combined images. As an alternative to employing a lower line-scanning rate to produce the signal of narrower bandwidth a lower picture rate may be employed. The partial pictures viewed by pick-up tubes 3a ... 3d may be interlaced. Fig. 3a shows a modification in which the partial pictures presented to the four pick-up tubes are interlaced. The original signals from V are applied to four cathode-ray tubes 1a . . . 1d and the tubes are controlled in sequence by a unit 7 so that each produces a different quarter of the image made up by displaying one line in every four. An inverse arrangement, Fig. 3b (not shown), is employed for reproduction. Where the number of lines forming the image is not divisible wholly by the number of recording channels employed, it is necessary that unit 7 should be controlled so that switching between the cathode-ray tubes occurs during certain selected half-lines whereby the same partial image is reproduced repeatedly on each tube. The Specification describes such an arrangement using four cathode-ray tubes for the French double interlaced 819 line system, Figs. 4 and 5 (not shown). The cathode-ray reproducing and pick-up tube combinations may each be combined in a single envelope. The reproducing tubes may operate with light of a colour most suitable for the pick-up tubes and which need not be visible. Reference is made without giving details to colour television in which the component colour informations appear separately on the reproducing tubes. When it is not desired to transmit the signals reproduced from the recordings, it is sufficient to combine the images from the cathode-ray reproducing tubes by suitable optical means and dispense with the scanners.