Patent GB-631414-A (GB)
Title: Improvements in or relating to telephone transmission systems
IPC: H04Q3/00
Filed: 1947-07-11
Abstract: 631,414. Multiplex systems. WESTERN ELECTRIC CO., Inc. July 11, 1947, No. 18479. Convention date, May 13, 1941. [Class 40 (iv)] Fragments of speech in one direction from simultaneous conversations between stations 11 at a terminal 45, Fig. 1, and stations 16 at terminal 46 are distributed over three lines 24, 25, 26 taken in rotation as they become idle. Each line is held until a pause in the speech making the end of the fragment allows holding relays to fall back. Separate lines 41, 42, 43 and distributing arrangements are provided for speech in the reverse direction. When a line is seized, the next idle line is selected in readiness for the next fragment. Separate lines 27, 44 are provided for V.F. signalling, the frequencies f1-f5 being allotted to the stations 11 and also to the corresponding stations 16. Transmission, Fig. 2. A distributer common to all the stations at terminal 45 comprises a selector switch 127 with two brushes, contacts corresponding to the three lines 24, 25, 26 and a stepping magnet 134. As shown, the brushes rest on contacts corresponding to line 24 and relays 77, 81 and 137 are operated. Speech from station 11 causes voicefrequency receiver 125 to operate relays 75, 76 and 82-86. Relay 86 connects the station to the line 24 and relay 85 operates magnet 134 to step the selector to find a contact that is marked idle. Relays 75, 83, 84 guard against double connections. Relay 82 provides a hold for relays 77, 81 from battery, and relay 76 dispatches a signal of frequency f 1 for the duration of the fragment. At a pause in the speech from station 11, the terminal apparatus of line 24 returns to normal ready to receive in its turn another speech fragment. Relays of a second station 11 are shown at A. Reception, Fig. 3. Voice-frequency signals are utilized to operate a selector switch 213 common to all stations at terminal 46 in step with the switch 127 at terminal 45. Each station 16 is provided with an individual switch 212 with one single wiper, a set of twin wipers and a stepping magnet 217. The frequency f accompanying a speech fragment from station 11 operates relays 243, 244, 245. Relay 243 connects line 24 to station 16. Relay 244 disables the switch 212 and relay 245 steps' the common switch 213 and the individual switches of idle stations to the contacts of the next idle line. At the end of the speech fragment, relays 243, 244, 245 fall back and the individual switch of station 16 is stepped until it is again in step with switch 213, when the magnet 217 is shunted by resistance 274 and no longer operates. Periodic check of synchronism. Whenever the wiper of switch 127 (Fig. 2) rests on the first contact, relay 137 is operated to send a signal of frequency fa which operates 271, 272 (Fig. 3). Relay 272 removes a shunt 274 from magnet 222 which, if it is not already on the first contacts, operates in series with shunt 274 and one of the resistances 273 until it finds the first contact, when it cannot operate again by reason of an equivalent shunt 276 applied by relay 271. The individual switches of idle stations are similarly connected. The boxes 301, Fig. 2, and 302, Fig. 3, represent similar equipment for speech in the reverse direction from terminal 46 to terminal 45.