Patent GB-1049449-A (GB)
Title: System of videophonic telecommunication
IPC: H04N7/14
Filed: 1963-12-11
Abstract: 1,049,449. Two-way combined television and telephone system. A. BELTRAMI. Dec. 11, 1963 [Dec. 11, 1962], No. 48854/63. Headings H4F and H4L. In a two-way combined television and telephone system the communicating stations A and B are provided with cathode-ray tubes 1, 1b which function alternately for periods of one television frame for (a) image reproduction and (b) image scanning in conjunction with a photo-electric cell 2, 2b. The system operation is controlled by optical waveform generators 3, 3b, driven by synchronous motors 4, 4b, that at the station (A) which originates the call being energized from the mains supply and that at the other station (B) being driven by the frame frequency component of the received signal. The waveform generators furnish line and frame components to control the scanning of the cathode-ray tubes, and square waveforms at half frame frequency which blank alternate frames of the signals from the photoelectric cells 2, 2b in stages 7, 7b and also similarly blank the modulation inputs to the tubes in stages 11, 11b. The telephone signals amplitude modulate line frequency pulses in stages 6, 6b to produce waveforms FA, FB which are combined with the video signal waveforms VA, VB in mixers 8, 8b to produce composite waveforms. The signals pass to line L via amplifiers 9, 9b and rectifier elements 10, 106, and are received via stages 11, 11b which separate the video signals and telephone signals and pass them respectively to the cathode-ray tubes 1, 1b and via integrator circuits 13, 13b to the telephone receivers. The signals from the two stations are arranged to occupy different amplitude ranges so that they may be separated by amplitude discrimination. A modification is described, Fig. 3 (not shown), which uses a radio communication channel. The arrangement is generally similar to Fig. 1, but television and telephone communication is effected alternately at predetermined intervals. The waveform generator also differs in that only the line frequency component is produced, the remaining component being produced by electronic circuits. A further embodiment is described in which the waveform generator is located at a control exchange for the system. Disturbance of the reproduced images by the alternate frames devoted to scanning may be avoided by the use of cathode-ray tubes with double layer screens which may be switched from visible light for image reproduction to infra-red as ultra-violet light for scanning. Alternatively scanning and reproduction may be effected on different areas of the tube screen. The waveform generators comprise cylinders or discs defining the waveforms in terms of areas of distinguishable transmissivity or reflectivity and co-operating the light sources and photoelectric cells. Provision may be made to furnish waveforms suitable for a number of different picture definitions constrained to a common transmission bandwidth by reducing frame frequency as line frequency is increased. The cathode-ray tubes may be formed with screens which have different degrees of persistence in different areas, the areas for image reproduction being selected in accordance with the frame frequency employed. Alternatively the screens may be in separate tubes.