Patent GB-705839-A (GB)
Title: Improvements in or relating to telecommunication exchanges
IPC: H04Q11/04
Filed: 1951-01-08
Abstract: 705,839. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Jan. 8, 1951 [Jan 6, 1950], No. 557/51. Class 40 (4)  To connect a calling line to a channel of a time-division multiplex trunk, a scanner in response to a calling condition causes the identity of the caller to be stored in an idle one of a number of registers which are scanned in synchronism with the timing of the channels, an electronic switch connecting the caller's line to the trunk when the register storing the caller's identity is scanned. In the system described there are three subscribers and two channels. The pulse forms shown in Fig. 7 are applied to the terminals indicated on the right-hand side of the Figure. When the line loop 1, 2, Fig. 1, is closed the potential applied by a 48-volt battery 8 to the line terminal 27 of a scanning circuit, Fig. 2, is raised to about -24 volts so that in a time position 43, forming one of a repeated cycle of time positions and characterising the calling line, and during which earth is applied to terminals 36, 37 of a rectifier gate, terminal 39 is brought up from the-36 volt potential at which it is normally maintained to-24 volts. An impulse regenerator 47, Fig. 3, converts this pulse to one of-100 volts from  -150 volts which is gated say to one.of the registers 60, 80, Fig. 4, the rectifier gates 50, 51 being opened during alternate scanning cycles. The calling pulse applied to terminal 64 say operates one or both of cold cathode tubes 61, 62 depending on the reference pulses applied to terminals 101, 102, and since in time position 43 terminal 102 is raised from -150 to-100 volts tube 62 is fired thus registering the caller's code. The codes set up in registers 60, 80 each associated with one multiplex channel are alternately applied to terminals 71, 72 by a multivibrator 79 which alternately connects negative pulses to terminals 75, 95. The code is translated by two pairs of triodes such as 103, 104, Fig. 5 and is applied to terminals 108 ... 111 of the rectifier gates, Fig. 6, controlling the effective connection of calling lines to the multiplex trunk 125. The pair of triodes 103, 104 function so that 103 is normally conducting but extinguishes to cause 104 to conduct when a negative potential is applied to terminal 71. Thus when tube 62 is fired -48 volts, earth, earth, -48 volts are the respective potentials of terminals 108 ... 111, and this combination allows current to flow through rectifiers 127, 128 to a 48-volt battery 119, so, that speech currents from transformer 5 are effectively connected to the multiplex trunk 125. When the caller's code is applied to terminals 108 ... 111 a negative pulse derived from the common point between the rectifiers 127, 128 charges condenser 20, and during the intervals when the code registered in register 80 is applied, condenser 20 discharges through a resistance 21. Thus, for the duration of the call, rectifier 17 is biased negatively so preventing the caller's code being set up in both registers at the same time. By using a greater number of pulse sources and say seven tubes in each register a group of one hundred lines could be served by a similar arrangement. The rectifier scanners may be replaced by cathode ray tubes such as those described in Specification 644,571.