Patent GB-837670-A (GB)
Title: Improvements in or relating to signal transmission systems
IPC: H04Q11/04
Filed: 1958-12-30
Abstract: 837,670. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Dec. 30, 1958 [Jan. 6, 1958], No. 42024/58. Class 40 (4). [Also in Group XL (c)] . A signal transmission system comprises a sampling gate for sampling the signal on a transmission medium, an amplifier, means coupled to the sampling gate for applying a signal sample to the amplifier at a higher voltage than that of said signal on said medium, an output gate for applying the output of the amplifier to said medium and means for enabling the sampling gate during one time interval and the output gate during a later time interval. This arrangement enables a single bilateral gated amplifier to be associated with, all the communication channels in a multiplex system by connection of a common link between the gated amplifier and consecutively operated channel gates. As shown in Fig. 1, a plurality of telephone stations 10 are connected in pairs by two-wire grounded transmission lines 11. The conventional switching system for interconnecting various stations is not shown. A gated amplifier 12 is connected over a common link 13 via a series of line gates 15 to a capacitor 14 in each of the transmission lines. A gate control circuit 16 applies pulses to enable each of the gates 15 in succession thereby applying successive signal samples stored in capacitors 14 via the link 13 and a sampling gate 20 to a series resonant circuit comprising an inductor 21 and capacitor 22. The gate 20 is enabled in unison with the operation of each of the gates 15 by pulses from the circuit 16, and is disabled when the voltages across the capacitor 22 is a maximum and is considerably higher than the input signal sample. An amplifier 23 is connected across the capacitor 22 and when the gate 20 is disabled, the amplifier output gate 24 is enabled and passes the amplified sample via the link 13 and gate 15 to the transmission line 11 which originated the signal. The corresponding gate 15 and the gate 24 are then disabled. Before the sampling gate 20 is activated for the next gated signal, a clamping gate 25 is activated to discharge the capacitor 22. The inductor 26 assists in the transfer of the signal through the gates, the gates being disabled in one half cycle at the circuit's resonant frequency. A time division multiplex system, Fig. 2, comprises a plurality of telephone terminals 27, 28, for local operation which are associated with a remote group such as 29 and with each other by a two-wire commonlink 30. Each terminal includes a repeater coil 31, filter 32, and line gate 33, a pair of active terminals in communication having their respective line gates 33 operated together so that signal samples are transmitted over the common link 30 during a time slot. A particular time slot in a cyclically repeated group of time slots is assigned to each pair of terminals in communication. A gated amplifier 20 to 25 as described with reference to Fig. 1 is located at any position on the common link 30 and by this means communication in either direction, between local stations such as 27, 28, or distant stations, such as 27, 29, is made possible with a single amplifier. The output signals from the amplifier flow both towards the sending and receiving terminals the original signal being reduced by the amplified sample transmitted toward the sending terminal and increased by the amplified sample transmitted toward the receiving terminal. Each of the gate circuits may consist of a pair of transistors, Fig. 6 (not shown), having common base and common emitter connections, a magnetic core being coupled to the base and emitter. Timed pulses from the gate control circuit are applied to the magnetic core to activate and disable the gate. An additional amplifier may be included between the common link 30 and the sampling gate 20. In a further arrangement, Fig. 5 (not shown), the circuit elements 20, 21, 22, 25 are duplicated and the two gates 20 operated alternately.