GB551034A - Transmission of picture telegraphy and like signals - Google Patents

Abstract

551,034. Picture telegraphy. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Nov. 6, 1941, No. 14326. Convention date, Nov. 7, 1940. [Class 40 (iii)] A start-stop system for the transmission of picture telegraphy and like signals comprises drums or other message carriers 1 rotating in steps at the transmitter, Fig. 1, and the receiver Fig. 2, in relation to scanning devices 12, 12 at a frequency depending on the depth of shade of the original being scanned. The scanner 12 at the transmitter contains a photo-electric cell and is connected to a valve 20 which controls the rate of charge and discharge of a condenser 26 in dependence on the depth of shade of the message at the point being scanned. At each charge of the condenser 26 a signal pulse is passed by a neon tube 23 to a transformer 24 connected to a signal transmitting apparatus 29, 30 through an amplifier 27 and a modulator 28. The amplifier 27 is also connected to a halfwave rectifier 32 with a load resistance 31 connected to the primary of a transformer 33, the secondary of which is connected through a rectifier 34 to a coil 11. Each rectified signal pulse causes the coil 11 to release a detent 7 and allow the drum 1 to be rotated one step by a motor 3 to scan the next point of the message. At the receiver, the modulated signal is received by the signal receiving apparatus 35, 36 and fed by a transformer 37 to a full-wave rectifier 40 which yields a signal pulse corresponding to the signal pulse passed by the neon tube 23 of the transmitter. This signal pulse is supplied to a neon tube 16 on the scanner 12 and also to a rectifier device similar to that of the transmitter for controlling a similar coil 11 to release the detent 7 to allow the motor 3 to rotate the drum 1 in steps at the same rate as the steps of the transmitting drum.