Patent GB-845798-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: GALVIN JOHN LESLIE
IPC: H04Q3/00
Filed: 1958-04-08
Abstract: 845,798. Automatic-exchange systems. AUTOMATIC TELEPHONE & ELECTKIC CO. Ltd. March 5, 1959 [April 8, 1958], No. 1094:7/68. Class 40 (4). During delay working conditions at a tandem exchange an operator rebooks an incoming call, tells the calling subscriber to clear, and subsequently sets up a connection to the wanted subscriber over a first outgoing 4-wire trunk and sets up a connection to the originally calling subscriber over a revertive call circuit to a second outgoing 4-wire trunk, the revertive call circuit being such that when the operator retires a through 4-wire path is provided which transposes the transmission pairs of the trunks. Incoming trunk lines reach operators' connect circuits CC over a mulitiple ISM, circuits CC also being accessible over a revertive finder RF. Outgoing trunk circuits OTCA, OTCB, equipped for V.F. signalling and dialling and connecting with 4-wire audio trunks or radio or line carrier systems, are available over group selectors TGSA, TGSB, or from 2-wire local selectors over multiple LSM. Hybrids HA, HB, allow the outgoing trunks to work on a 2-to-4 or 4-to-4 wire basis. Access to local selectors is had over the 2-wire multiple LS, as shown in group selector TGSA. To call the wanted subscriber the operator makes a loop from her position OPC to operate feed-relay AA which repeats the first digit to set group selector TGSA to find and seize an outgoing trunk, such as OTCA, from which digits are repeated by feed-relay 2AA to modulator SM. In the group selector relay H was operated and held over the P-wire and prepares circuits for hybrid and pad switching relays AFW and APC in the line AB. On receipt of a reply signal, receiver VFR operates contacts ax1 to bring up relays AVF and ADD in train to reverse polarity in the loop of feed-relay 2AA and so bring up relay DC to signal the operator. With keys RC and SK, the operator now starts a finder RF, allotted by a chain circuit (not shown), which connects with the operator and operates and locks up RH. A loop circuit is made to feed-relay RA which completes a loop circuit for feed-relay BA in group selector TGSB. A digit is now repeated to and by BA to set selector TGSB which extends the operator to a 4-wire trunk such as OTCB over which further digits are repeated by 2BA and sent as audio pulses to obtain the originally calling subscriber. When TGSB was seized relay BH locked up and prepared circuits for pad and hybrid switching relays BFW and BPC, relay FWA being operated in a series circuit with BPC which does not pull up. In response to a reply signal over a V.F. receiver, RD operates to reverse current to reverse the current through feed-relay RA and operate DA to signal the operator. The operator may now retire by restoring key SK, relay FW responding in circuit with pad-switching relay APC which does not pull up. Relay FW connects the + and - wires of OTCA to the A and B wires of OTCB, and vice versa, and energizes relays AFW and BFW to remove the hybrids HA, HB. Should one party be obtained over a 2-wire line, such as over multiple LS, an earth is put on the A wires of all 2-wire outlets so that, if the 2-wire outlet is over TGSA, earth over SKI, contacts fw3 and bh6 operate BPC to switch out pads in the 4- wire circuit OTCB. Unspecified additional circuitry may switch out pads when a 4-wire trunk is seized directly over the 2-wire multiple LSM.