Patent GB-1017123-A (GB)
Title: Colour television transmission systems for transmission by means of at least one satellite
IPC: H04N11/12
Filed: 1962-11-05
Abstract: 1,017,123. Pulse code modulation systems; colour television; radio signalling. G. VALENSI. Nov. 5, 1962 [Nov. 3, 1961; Nov. 29, 1961; May 28, 1962; July 13, 1962; Sept. 21, 1962], No. 41744/62. Headings H4F and H4L. Colour television is transmitted using pulse code modulation via one or more artificial satellites. Satellite communication system.-The system shown in Fig. 1 provides long range colour TV from ground station EV via satellites S1 to S4 to ground station receiver RV<SP>1</SP> and short range telephony from ground transmitter ET via satellite S2 to receiver RT and from transmitter ET<SP>1</SP> via satellite S3 to receiver RT<SP>1</SP>. As the satellites follow the orbit, each satellite at a certain time will have to change-over to the operating mode of its predecessor and this is achieved by switching signals from EV, ET and ET<SP>1</SP>. Transmission from ground to satellites is in one band, different carrier frequencies being used for telephony and television, and reception from satellite to ground is in another band. A third frequency outside these two bands is used for switching signals. Artificial satellite, Fig. 2.-As long as satellite S1, Fig. 1, remains in the range of TV transmitter EV a switching signal C1 received via aerial ac and switching device 505 establishes and maintains connection for the TV signals from the receiving aerial ar via a filter 508, the first input 531 of TV transmitter 514, where the signals are frequency-changed, gate 519 and amplifier 520 feeding the aerial ce transmitting to the preceding satellite. When the satellite comes into the range of the telephone station ET, aerial ac receives a switching signal C2 which causes the telephone signal received on aerial ar to be supplied via filter 507, frequency-changer and transmitter 517 and gate 518 to the transmitting aerial ae cooperating with receiver RT, Fig. 1. Reception of switching signal C2 breaks the previous connections for the TV signals which are now supplied via aerials cr1, cr2 from the following satellite to a pulse regenerator 511, second input 532 of transmitter 514 and gate 519 for retransmission via aerial ce, gate 515 being closed. These connections are maintained by the switching signal C2 received thereafter from transmitter ET1. When the satellite comes within range of transmitter EV<SP>1</SP> it receives switching signal C3 and the received TV signal is supplied via pulse regenerator 511, second input 532 of transmitter 514, gate 515, frequency-changer 516 and aerial ae for transmission to receiver RV<SP>1</SP>. The received signals from aerials cr1, cr2 are also supplied to a device 512 providing a difference signal which is a a function of the angle between the correct position and the real position of the axis of the satellite, assuming the following satellite to be correctly positioned, and is applied to an attitude control device 513 controlling gas jets from respective pipes P1, P2. An aerial A, permanently energized by a transmitter 502, acts as a radio beacon. Colour television systems using pulse code modulation.-Two arrangements are described: (1) using the NTSC system and, (2) using the system based on the mapping of the colour triangle, .Fig. 15 (not shown), with a colour subcarrier which is amplitude modulated by a voltage proportional to the number of the triangle sector corresponding to the transmitted colour. The minimum pulse coding requirements are discussed and it is stated that the following accuracies suffice, (a) 30 luminance levels, (b) 30 colour-hue levels, and (c) 2 values for the colour-saturation signal. As five code pulses produce 32 levels, in the NTSC system the 31st and 32nd levels of the luminance signal, i.e. 01111 and 11111 are allotted to the line and field sync. signals respectively, and the two lowest levels of the colour-hue pulse code signals correspond to " no colour" (black, grey or white). At the end of each scanning line a timing pulse of duration longer than that of a code pulse is transmitted. Cathode-ray tube quantizing and coding devices are described, Fig. 10 (not shown). At the ground transmitter the respective video components are derived from the incoming NTSC signal and these components are converted into corresponding p.c.m. signals for transmission via the satellites. At the ground receiver the p.c.m. signals are decoded and may be reconstituted into conventional NTSC form using a functiongenerating cathode-ray tube, Fig. 21 (not shown). The other television system is pulse coded in a similar manner and transmitting and receiving arrangements for both systems are described. In a modification more than one timing pulse is transmitted during each scanning line. A phase detector used in the ground transmitting station for deriving the hue signal from the modulated colour subcarrier in the NTSC system prior to pulse coding is described. A sine wave oscillator generates a wave at the subcarrier frequency and having the same phase as the " colour burst," and a filter selects the chrominance signal from the incoming video signal. These two waves are converted into similar rectangular waves of the same frequency and amplitude but having a characteristic phase difference and added so that the combined waveform has one portion of double-amplitude where the two waves overlap in time, the duration of which is proportional to the phase difference. These duration modulated pulses are selected by an appropriately biased amplifier, converted to amplitude modulated pulses in an integrating circuit and demodulated. The timing pulses transmitted at the line scanning frequency are duration modulated to carry the accompanying sound signals.