Patent GB-434891-A (GB)
Title: Improvements in or relating to television, sound and like communication systems
IPC: H04N7/084
Filed: 1934-04-09
Abstract: 434,891. Multiplex transmission. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Branson, H.; 1313, Fillmore Street, Philadelphia, U.S.A.) April 9, 1934, No. 10692. Convention date, April 8, 1933. [Class 40 (iv)] [See also Group XL] Relates to talking-television systems of the kind described in Specification 434,890 in which picture signals and sound signals are transmitted alternately on the same carrier. According to the invention the sound signals are stored in a cathode-ray transmitter tube during the transmission of picture signals ; they are then transmitted at high speed during a brief pause at the end of the line-scanning operation. At the receiver they are stored in a similar cathode-ray tube and are reproduced at normal speed. Cathode-ray tube for storing, transmitting and receiving sound-signals. The tube 1, Fig. 4, has an electron-gun with an indirectly heated cathode 5, a grid 7 and an accelerating- electrode 9. The target 19 is an insulating plate studded with caesium-sensitized silver globules 21 which form separate condensers with the conductive plate 23. The cathode stream is moved over the target 19 by means of deflecting-plates 11, and the sorting-power of the tube is brought into and out of action by a conical control electrode 17. When this electrode 17 is negative, Fig. 5 (not shown), the globules 21 acquire a charge from the cathode stream as it passes over them, so as to store up signals represented by variation of the intensity of the cathode stream, but when the electrode 17 is positive the globules are discharged so as to give an output signal, the cathode stream being arranged to have uniform intensity during this latter period. At the transmitter the cathode-stream moves slowly during the storing-period and returns quickly during the transmission period, but at the receiver the reverse of this takes place. A synchronizing- signal is sent when the cathode stream reaches the segment 69. Transmitting. The picture signals P, Fig. 2a, derived from a cathode-ray or other transmitter are passed through an amplifier which is operative for <9>/10 of each frame-scanning period (a frame-synchronizing signal being transmitted during the remainder of this period) ; then through a further amplifier which is operative during a portion T1 of each line-scanning period T. The remainder T2 of each linescanning period is allotted to the transmission of (i) a line-synchronizing signal and (ii) a compressed sound signal. Sound signals are first recorded and then transmitted, and for the former purpose they are passed through an amplifier which is operative during two portions A All, Fig. 2b, only of the period T1, then through the cathode-ray tube 1, Fig. 4, at such a time that the signals are recorded at the natural speed, but are subsequently passed on at a speed nine times as great during part of the period T2, which period also accommodates the line-synchronizing signal E. Thus, as is shown in Fig. 2c, the picture signals P, synchronizing signal E and compressed sound signal A A<11> are sent in succession on the same carrier. These operations are co-ordinated by means of a synchronizing and controlling device 73, Fig. 10 (not shown), of the kind described in Specification 395,499, [Group XL]. Receiving. At the receiver the picture is seen and the sound is heard during the period T1, but the sound signals are recorded and the synchronizing signals are received during the period T2. Thus the compressed sound signals are recorded at high speed during the period T2 at the receiver by means of a tube similar to the tube 1 used at the transmitter, and are then reproduced at normal speed during the following period T1. The operations at the receiver co-ordinated by a synchronizing and controlling device 92, Fig. 13 (not shown).