Patent GB-561276-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1942-11-10
Abstract: 561,276. Automatic exhange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. T. Nov. 10, 1942, No. 15863. [Class 40 (iv)] In a system in which numerical impulses are sent over a long junction, the conditions appropriate to impulsing are established at the outgoing end in response to the seizure of the junction and speaking conditions are introduced-as the result of a register-sender at the incoming end completing its operations. The method of signalling is similar to that employed in Specification 560,120, in which impulses are sent by shunting out the battery supply to the junction and are received by two gas-discharge tubes which are triggered into operation alternately by the rise and fall of current. The junction is associated at the incoming end with a first code selector and a mechanical regenerator is used for repeating the received impulses to the A-digit switch and register-translator. Normal operation.-Upon seizure of the junction, e.g. by a first selector, line relay A operates relay RP which applies battery and earth to the junction through relay RS and connects in the line termination YM, QC1. Relay RS energizes over the junction and connects up RPR, which locks and shunts the battery supply to the junction, thereby releasing RS. Relay A repeats impulses by intermittently removing the shunt. At the incoming end, where, as in Specification 560,120, the gasdischarge tubes GTA, GTB are coupled to the junction by a transformer T2, the voltage pulse resulting from the shunt imposed by RPR triggers the tube GTA and energizes relay PZ, which brings in a series condenser QD to hold itself temporarily and extinguish the tube. Release relay 1B operates and connects up relay 1RR in the first code selector, whereupon hunting for an A-digit switch takes place. During impulsing, the tubes GTB, GTA are triggered alternately and control relays PS, PZ, and relay PB is operated by PS to extinguish the GTB and is released by PZ. Relay PS repeats the impulses to the setting magnet RM of the regenerator and holds until the latter operates. The end of an impulse train is determined as in Specification 549,047 by a timing circuit comprising a condenser QJ and neon tube NTB which controls relay TZ and is started at the first impulse of each train by the operation of relay TS. When relay TZ operates, it disconnects TS and connects up the start relay ST of the regenerator, but the latter does not begin to retransmit until relay SS operates in response to the seizure of an A-digit switch. When the register-translator releases after completing its operations, the relapse of SS connects up relay SK which extends the junction to the first code selector, and battery and earth are fed back through relay RR to operate RS at the outgoing end, whereupon relay RP is released by short-circuiting and completes the talking circuit. The reply of the called party causes a currentreversal over the junction to operate relay D in the usual way. The various line relays are shunted by condensers to block high-frequency surges. Upon release by the calling party, the relapse of RPR opens the circuit of RS, RR and the latter disconnects SK. Irregular conditions.-If the calling party delays dialling, relay SS is eventually released by timing equipment and connects up SK to extend the junction to a source of NU tone in the A-digit switch. If too many digits are dialled, the release of SS causes the rapid discharge of the extra digits before SK operates. If no idle A-digit switch is found and the subscriber hangs up after dialling one or more digits, PS delivers a further impulse to the regenerator and PB remains held. The operation of TZ by the timing circuit releases 1B and the stored digits are discharged rapidly, after which switching relay SK energizes and, since PB is up, opens the circuit over the junction for RS. At the outgoing end, the junction is re-guarded after the relapse of RPR by RP which is held until RS is released. If the subscriber hangs up prematurely after an A-digit switch has been seized, the action is similar except that the relapse of 1B disconnects 1RR to free the A-digit switch and release SS. Specifications 458,095, 469,184 and 556,326 also are referred to.