Patent GB-225553-A (GB)
Title: Improvements in and relating to television systems
IPC: H04N7/04
Filed: 1924-11-25
Abstract: 225,553. Westinghouse Electric & Manufacturing Co., (Assignees of Gardner, J. E., and Hineline, H. D.). Nov. 28, 1923, [Convention date]. Television apparatus. - A combined television and telephonic system operating by wireless transmission utilizes a single carrier wave which is modulated by currents representing respectively the varying illumination of the picture and the telephonic currents, and also by two alternating currents of definite frequency serving at each station to traverse an electron stream over all points of the picture in succession. Fig. 1 shows the transmitting circuits, and Fig. 2 the receiving circuits. A short-wave oscillator 3 coupled to an aerial 5 is connected to a modulating valve 6, the grid of which is under the influence of four separate sources of modulating potential. The telephonic or musical communication affects a microphone 26 the circuit of which is coupled through an amplifier 24 to a valve modulator 23<a>. An oscillator 22 generating currents of low radio frequency has its output modulated by the valve 23<a>, and the modulated output is applied from coil 23 through a condenser to the grid of the valve 6. Oscillators 10, 11 of frequency of the order of 1000 cycles and 16 cycles respectively are also connected to the grid of the valve 6. These oscillators also energize coils 12, 13 placed at right angles to each other adjacent to a cathode ray tube 14 thereby causing a narrow stream of electrons to traverse successively every point on a fluorescent screen 18. The tube 14 has a tubular anode 17, a screen 16 with a small central aperture, and a cathode 15. The cinematographic or other transparent picture to be transmitted is mounted between the screen 18 and an optical system 21 which focuses the light from the picture on to a photo-electric cell 9. The light and shade at the successive points of the picture cause a variation of current through the cell 9, which is amplified by the valves 7, 8 and applied to the grid of the modulator 6. The radiated wave thus carries four separate modulations. At the receiving station, the short carrier wave is amplified by the valves 28, 32 and rectified by the valve 34. The low radio-frequency corresponding to the valve 22 at the transmitter is selected by the tuned circuit 57 in the rectifier plate circuit and is passed to a further rectifier 52. The resulting telephonic current is passed through the valves 34, 32, 28 in that order, these valves acting as dual amplifiers, and giving an amplified reproduction in the instrument 56 coupled to the plate circuit of the valve 28. The currents of 1000 cycles and 16 cycles are selected by tuned transformers 36, 37 and valves 39, 41 and serve to traverse an electron stream over a fluorescent screen 47 arranged in a cathode tube 43 similar to that used at the transmitter. The intensity of this electron stream is controlled by a grid 45, the potential of which is varied (in accordance with the light and shade variations at the transmitter) by means of the coupling 38 and amplifier 50. The varying fluorescence of the screen 47 is focused on to a screen 48 through an optical system 49.