Patent GB-297152-A (GB)
Title: Television systems
IPC: H04N7/14
Filed: 1927-06-17
Abstract: 297,152. Beatty, W. E., (Bell Telephone Laboratories, Inc.). June 17, 1927. Television.-A combined telephone and television system is so arranged that each subscriber can see, be seen by, and converse by telephone with, any other subscriber to whom he is connected through an exchange. Picture analysis and synthesis. A single rotating disc 21 carrying spirally arranged lenses or apertures is used for receiving and transmitting at each station. It is provided with two spirals, one of which may be of smaller radius than the other, or alternatively the two spirals may be similar but in opposite halves of the disc. or they may be displaced relatively to one another by any suitable angle. The subscriber 9 is illuminated by a mercury vapour lamp 11 and stands in front of an aperture in a screen 24. An image of the subscriber is therefore projected by the mirror 26 and lens systems 27, 30, and traversed by the lens spiral carried by the rotating disc 21 so that successive elements of the image affect the photo-electric cell 31. Incoming signals from a distant station vary the luminosity of a lamp 33, and a fluctuating pencil of light passes via the lens spiral carried by the disc 21, the mirror 34. reversing prism 35, and' mirror 36 so that a picture of the distant subscriber is seen through the apertures in the screen 24. The left-and-right transposing prism 35 converts the received mirror-image into a normal image. In order that the subscriber 9 may not be dazzled, the source 11 of illumination is chosen so that its ratio of photoelectric to visual efficiency is a maximum; or alternatively the positions of the source of illumination 11 and photoelectric cell 31 may be interchanged, so that the subscriber is illuminated by a moving spot of light. Combined telephony and television. Each station is connected to an exchange 100 bv four channels, the channel 40, Fig. 1, being allotted to two-way telephony, the channel 41 to outgoing television signals, the channel 42 to synchronizing currents, and the channel 43 to incoming television signals. Synchronization is effected by coupling the driving motor 22 at each station to a synchronous generator 23 connected to the synchronizing channel 42, and the synchronism is preferably controlled by a master generator at the exchange. The four channels may be superimposed as shown in Fig. 6, where the synchronizing channel provides direct transmission while the other three channels employ carrier current; but in modifications all four channels may be carrier channels, or the television channels may be wireless while the telephone and synchronizing channels are wired. In the arrangement shown in Fig. 6, the incoming side of the hybrid coil 54 is connected through demodulators 55, 55<1>, to the television receiver 33 and through the hybrid coil 58 to the telephone set 10. The synchronizing generator 23 is connected to the outgoing side of the hybrid coil 54, as are also the television transmitter 31 (by way of the modulator-amplifier 51 with oscillator 52) and telephone set 10 (by way of the hybrid coils 58, and modulator-amplifier 51<1>). All four channels are wired to the exchange 100 through the pair 60, and they are separated from one another by filters 53.