Patent GB-403397-A (GB)
Title: Improvements in or relating to the transmission and reception of sounds and of combined pictures and sounds
IPC: H04N7/084
Filed: 1932-03-19
Abstract: 403,397. Transmission systems. WALTON, G. W., 2, Dean Street, Soho, London. March 19, 1932, No. 8255. [Class 40 (iv).] A method of transmitting sound, particularly for use in combined sound and picture transmission, comprises the stop of converting sound into an optical image in which frequencies are represented by positions in the image, and intensities by brightness. The image is scanned, it may be together with a picture image, and swept over a photo-electric cell in the output of which original voice frequencies occurring simultaneously are represented by impulses occurring at different times during the scanning period dependent on the voice frequency. These impulses may be transmitted over a line or recorded, reproduction being effected by a similar reverse process. In the transmitting arrangement shown in Fig. 1, voice frequencies from microphone 15 are amplified at 16 and modulate a carrier at 17. The modulated carrier is fed to transformer 10, the secondary of which is centre-tapped and connected to two oscillatory circuits including a discharge device comprising a coil 2 common to both circuits and electrodes 3, 4, having an elongated gap between them and discharge gaps between the electrodes and the coil. The voltage of source 11 is such that normally with an unmodulated carrier no discharge takes place between coil 2 and electrodes 3, 4. A modulated carrier however causes discharges between the coil and the electrodes, the discharge for any particular frequency taking place at a definite point along the electrodes as described in Specification 397,880. Different frequencies occurring simultaneously produce simultaneous discharges at different points. An image of the gap produced by lens 21 is swept over photoelectric cell 26 by an oscillating mirror 22 to produce impulses in the output circuit representing the original sound as previously described. Alternatively, the condition of the discharge device may be recorded and an image derived from the record used to activate the cell 26. When used for combined sound and picture transmission a, one-dimensional image of the picture 49 may be formed in the plane of the discharge gap, or of an image thereof, or of the record, by an optical system involving an echelon device 51 as described in Specification 328,286, [Class 40 (iii), Telegraphs, Electric]. The picture may be transmitted as described in Specification 403,395, [Group XL]. The discharge device may comprise a coil and a single bar electrode or two bar electrodes without a coil, the two oscillating circuits of Fig. 1 being replaced by a single circuit. Various forms of the discharge device described in Specification 397,880 may also be used. To confine a discharge to a particular turn of the coil 2, the coil is wound on a grooved former as shown in Fig. 5. The reproducing arrangements, Fig. 6, comprise a light source 56 controlled by incoming impulses and from which light is swept by a mirror 22, oscillating in synchronism with the transmitting mirror, over a gap in an electrode 57 adjacent to a coil 2. The portions of the coil 2 adjacent the electrode 57 are coated with photo-electric sensitive material and when light falls on any portion of the gap, the emission closes a circuit over such a portion of coil 2 that the resonant frequency of circuit 9, 10, 13 corresponds to the original transmitted frequency. Valve 31, normally just off oscillation, oscillates correspondingly and the signals are detected and reproduced at 38, 39 after a carrier has been added at 36. The received sound currents may be recorded on a film which replaces the discharge device 57.