Patent GB-367915-A (GB)
Title: Improvement in television system
IPC: H04N3/12
Filed: 1930-11-29
Abstract: 367,915. Television. COMMUNICATION PATENTS, Inc., 60, Broadway, New York, U.S.A. Nov. 29, 1930, No. 36066. Convention date, June 25. [Classes 40 (iii) and 40 (v).] In a television system the current impulses which are used to produce the scanning beam serve also to produce the carrier current which is modulated by the picture signals. The current impulses are preferably produced from a thermionic valve distributer. A station of a two-way television and telephone system, Figs. 2 and 3, has a scanning device 40, Fig. 2, comprising conductors 41, 42, 43 .., 44, 45, 46 .. energizing light sources, e.g. neon lamps or spark gaps, located at their intersections. The light sources are connected through transformers 40 .. 57 .., Fig. 2, to transformers 76, 78, 79 .., Fig. 3, in the output circuits of valves 59, 60, 61 .. of a thermionic valve distributer. The valves are connected in cascade so that an impulse will circulate round the system, delay devices 63 .. 66 .. connected between the plate of one valve and the grid of the next governing the speed of circulation. A loud-speaker 100, Fig. 2, is connected to a transformer 109, Fig. 3, in the output circuit of valve 57, a microphone 101, Fig. 2, is connected to a transformer 110, Fig. 3, in the input circuit of valve 58, while a photo-electric cell 105, Fig. 2, is connected to a transformer 88 in a modulating circuit 86. An impulse circulating in the valves 57 .. 61 energizes each light source of the scanning device, the loud-speaker and the microphone circuit in turn, at the same time producing a high-frequency oscillation in the transformer 84, through the third windings of transformers 109, 82, 76, 78, 79, which oscillation is modulated by the photo-electric cell currents for transmission. When the valve 58 becomes conducting, no light source in the device 40 is energized and the transmission of sound takes place without transmission of picture signals. The interruption of the sound transmission takes place at a super audible frequency. The output of the modulator 86 is connected to a transmitter 91 adapted to alternate in function as a receiver at a super-audible frequency. The received impulses are applied to all of the input transformers of valves 57 .. 61 and the circulating impulse renders each valve in turn conducting so distributing the received impulses into their respective circuits. A common bias battery 72, Fig. 3, is in circuit with a resistance 73 in parallel with two reversed rectifiers 89, 99 in the transmitting and receiving circuits respectively. When the generators at the two stations are in synchronism, the rectifiers neutralize and no change in grid bias occurs, but if the synchronism fails, a differential voltage is produced across the resistance 73 and varies the bias and therefore the frequency of one or other of the generators. A key 74 enables the image to be framed, or the circulation of an impulse to be started, by shortcircuiting the battery 72. The scanning device 40 may be energized by two interconnected thermionic valve generators, one supplying the horizontal conductors 41, 42, 43 .., Fig. 2, and the other the vertical conductors 44, 45, 46 . ., Fig. 2 (Fig. 4 not shown). Each light source may co-operate with a quartz rod or a tube to prevent reflection losses, Fig. 6 (not shown). Specification 368,330 is referred to.