Patent GB-502545-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1937-10-06
Abstract: 502,545. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., BEALE, C. E., RICHARDS, I. T., and PEARCE, O. A. Oct. 6, 1937, No. 27138. [Class 40 (iv)) In a system comprising a main exchange and sub-ordinate exchanges in which inter-exchange calls and in some cases local calls are set up from the main exchange, a tandem exchange is equipped with discriminating selector repeaters the operation of which is dependent on the destination of the call. The system described with reference to Fig. 1 comprises a main exchange M and a tandem satellite TS in which subscribers set up local calls but are connected to a manual board MB at M when requiring an external call, and tandem and terminal revertively controlled exchanges (RCX's) which have all calls set, up by the operator at MB. Calling subscribers at the tandem and terminal RCX's R and TR are connected non- numerically to a both-way junction to the satellite TS at which is seized a discriminating selector-repeater D1 associated with a non- numerical switch JH3 which hunts for an idle junction to M. The operator responds and sets up a checking connection to the calling party, the first digit raising the bi-directional switch of the selector-repeater D1 to a level at which a relay operates to condition the circuits for repetition of subsequent digits over the seizing path to the RCX's to set the local link in the calling exchange. D1 does not hunt in this case. The checking connection is then broken down by a high voltage pulse from the operator who may complete the call in or through the main exchange or may re-set D if the call is for the satellite TS, or one of the RCX's, or for another RCX accessibie over the satellite. If the call is to RCX, TR or R, the selector repeater D1 is re-set as described for the checking connection but if for another RCX or the satellite, DI after responding to the first digit hunts for an idle junction or local selector as the case may be. Calls incoming to the system are set up by the operator over selector-repeater SR. Calls originated by a,subscriber at satellite TS are completed automatically over a local discriminating selector-repeater LD if the call is local as determined by the first digit: If not, an associated non-numerical switch JH1 hunts for a main exchange junction, and the operator completes the connection after setting up a checking connection to the calling party. The detailed description relates to the operation of the discriminating selector-repeaters D1, LD and their associated junction switches JH. The tandem RCX TR may have 10-party line. equipments as described in Specification 476,813. Call from RCX subscriber. The call comes into the discriminating selector repeater, Figs. 2 to 4 (corresponding to D1 or D2, Fig. 1) as a pulse of ringing on lead -1 and operates relay R, shunted by a rectifier, which locks up and operates B. Relay IC pulls up and busies the P2 lead in the multiple of the selector-repeaters, and RC connects magnet JHM to wiper JH4 of the non-numerical switch which hunts for an idle main exchange junction. The junctions are busied by ground over ja4, jb1 for incoming calls and ground over relay KA for outgoing calls so that JH steps until it finds absence of ground whereupon K operates in series with magnet JHM and relay JA in parallel both of which are inert in this circuit. K releases RC slowly and connects KA to JA, both of which operate, the main exchange junction + 3, -3 being switched through and disconnected from the inlet +4, -4 of the incoming selector-repeater (SR, Fig. 1). During the release period of RC, a pulse of ringing from common lead 11 is connected to wire -3 of the main exchange junction. When the operator responds by looping the junction, AO pulls up and operates RD which prepares the impulse circuit for the vertical magnet, holds B over its lower winding and connects R (lower) and DI across the junction from the RCX. If the local links in the RCX are busy at the time of making the call, the calling line relay looks up until a link is idle, and the calling party may have replaced his receiver. If he has, DI is operated and also battery reversing SY, since C has been operated, thereby giving the operator the necessary supervision. If the operator finds that the calling party has hung up she grounds the two wires of the main exchange junction to operate differential relay OC which repeats the signal by grounding the wires of the junction to the RCX which brings about the ringing of the calling party, DI and SY being operated on his reply. Operator sets up and clears a checking connection to calling party. The first 'digit (7), which designates the junction over which the call was made, is repeated by AO to the vertical magnet VM and relays CJ and C, relay H being  operated on the first step to short-circuit the original operating winding of C. Relay CJ disconnects the shunt path NT, TO from the loop and RD remains held during intermittent short-circuiting, the rectifier MRB preventing magnet VM from being slowed by the parallel resistance YB. At the end of the digit, CJ and C fall back and relay OE operates over the vertical bank VB to replace the bridge on the calling side of the repeater by a loop over I and D including contacts of impulse relay AO. Relay H released by OE permits C to reoperate. By avoiding use of the hunting movement of the selector to make connection with the calling junction, incorrect connections are impossible when more than one junction is provided to the RCX. Further digits are repeated over the RCX junction, CJ being re-operated to shunt relays I and D during impulsing. If the number given by the calling party is correct, the operator receives busy tone but as a further check she may break in and ask again by-operating differential relay OC which, as before, repeats the signal to the RCX by grounding both junction wires. The clearing of the checking connection is effected by a pulse of high voltage from the operator which breaks down discharge tube NT to operate TO whereupon RR pulls up, locks in series with OE and short-circuits condensers QC, QD to extend the high voltage pulse to the RCX where it operates a further relay over a 'discharge tube to release the checking connection at the RCX. At the selector-repeater, RR disconnects D and I to prevent operation by the pulse, completes a local holding circuit for AO, and releases C to complete a self-interrupting release circuit for rotary magnet RM, the selector being of the so-called rectangular release type. When the selector has released, RR and OE fall back re-connecting AO to the main exchange loop and reinstating the bridge to the RCX junction. Completion of connection and release of equipment not in the line of connection. If the call is for a subscriber on the same RCX the first digit operates OE as described for the checking connection and further digits are repeated back over the RCX junction. At the end of the 1st digit received at the RCX the reverse battery supervision of the calling party is disconnected to prepare for supervision of the called party. When this party replies, relay D operates followed by DD which brings up battery reversing relay SY. The withdrawal of the operator releases AO whereupon RD releases quickly since shunting and holding circuits have been opened by DD. Relays B and K also fall back, the non-numerical switch JH goes home, and the relapse of B completes the self-interrupting rectangular release circuit of the numerical switch, in.this case from ground on common lead 10. The RCX junction is maintained by relay IC until release is completed. If the call had been for a subscriber on another RCX accessible over the satellite exchange, the first digit raises the repeater to a level e.g. 6 on which hunting is initiated by the operation of SA over the vertical bank. The circuit of H (lower) in this case is not opened but passes over the interrupter contacts of RM, so that H is maintained energized over its upper winding during hunting by ground on busy junctions. On the first idle junction, both windings of H are de-energized and the relapse of this relay opens the circuit of RM and permits C to re-operate to complete a seizing loop over D and I to the RCX, further digits being repeated thereto by AO. On reply of the wanted party, D, DD and battery reversing relay SY operate as before and on withdrawal of the operator AO and RD fall back to release K and home the non-numerical switch. The relapse of K also completes the speaking path from the calling junction to the numerical switch, which does not release in the present case since B is held by R which is operated in a bridge R, DI across the calling junction. When the calling party hangs up, R falls back followed by B and C which complete the release circuit. Busy conditions. If switch JH finds all the main exchange junctions busy, it proceeds to last contacts which are disconnected so that K operates in series with JHM but there will be no circuit for KA. Busy tone from lead 12 is thereupon connected to a 3rd winding of AO. If the numerical switch finds all junctions busy, 11th step springs S release H and connect busy tone to AO. Calls from the main exchange. When the incoming selector-repeater (SR, Fig. 1) is seized, JB is operated over lead P4 to busy the junction in the banks of the non-numerical switch and when the selector-repeater seizes an RCX junction, ground on P2 operates OG to switch the junction to the selector multiple. The relays JB, OG form part of the both-way junction circuits BE3, BE1, respectively, of Fig. 1.. Local selector-repeater. Figs. 5 to 7, (LD, Fig. 1). When the switch is seized by the call finder over leads + 1, -1, relays A, B, BA and C pull up and dial tone is returned from lead 13. The first digit is repeated to VM, C and CJ and, in the case of a local call, is absorbed by the operation of M over a strapping on the vertical bank VB when CJ rel