Patent GB-538037-A (GB)
Title: Improvements in or relating to telegraph signalling systems
IPC: H04L5/22
Filed: 1940-03-06
Abstract: 538,037. Multiplex telegraphy. TELETYPE CORPORATION. March 6, 1940, No. 4163. Convention date, March 13, 1939. [Class 40 (iii)] In a distributer multiplex telegraph system, for transmitting messages from a variable number of transmitters to corresponding receivers, destinationselecting signals are transmitted over one channel and character-selecting signals are transmitted over another channel, the two sets of signals being restricted to their respective channels. This enables the line to be fully utilized, since the line may be shared equally by all the active transmitters or if only one transmitter is active continuous transmission takes place. In one system described, a code signal representing a character and its destination is sent from each active transmitter in turn, but in a modification a complete line of characters may be transmitted from each transmitter in turn, the necessary switching operation at the end of the line being effected in a page printer by the usual carriage return signal sent at the end of each line, or in a tape printer by a relay operated by a ratchet counter effective after say 70 characters have been transmitted. In the start-stop system shown in Figs. 1 and 2, the 5-unit character code signal sent from contacts 25 of the distributer is preceded by a destination code signal represented by potential on one or other or both of the contacts 27, 28 of the distributer, these signals energizing one or other or both of the relays 63, 64, Fig. 2, to select one of the three printers or lines 71, 72, 73. The contacts of the three tape transmitters 21, 22, 23, Fig. 1, are connected to contacts controlled by cams 12, 13, 14 on a clutch-driven shaft which can be stopped in one of three operative positions by engagement of a catch with the armatures of magnets 44, 45, 46. Each set of contacts comprises five contacts 26 connected to the tape transmitters, and additional contacts such as 29, 33 connected differently to battery so as to energize one or other or both of the contacts 27, 28. If all the transmitters are active and their tape-controlled contacts are open, each transmitter operates in turn to send one character, but if one or more transmitters are inactive, the cam-shaft is not arrested in the positions corresponding to such transmitters, and the other transmitter or transmitters operate in turn. At the receiver, the character code signals are stored in the relays 1 to 5, and repeated by a second start-stop distributer 66 to the printer or line selected by relays 63, 64. In a modified system, Figs. 3 and 4 (not shown), one of three lines is selected by sending an impulse over one of three distribution contacts preceding the character-code contacts, and the clutch-driven shaft remains in each position while all the characters of a line are transmitted, the shaft being moved to the position corresponding to the next active transmitter on the receipt of the carriage-return signal, which controls a relay chain to slip on the shaft. Alternatively, this may be effected by a ratchet counter, which is moved one step at each rotation of the distributer and is released after a predetermined number of such steps, or should all the tape-controlled contacts remain open indefinitely.