Patent GB-797849-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: GALVIN JOHN LESLIE
IPC: H04Q3/00
Filed: 1956-01-31
Abstract: 797,849. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Jan. 3, 1957 [Jan. 31, 1956], No. 3009/56. Class 40 (4). At a tandem exchange a uniselector TS is controlled by a digit switch DS to make fourwire connections over one set of wipers and two-wire connections over another set of wipers. If two-wire connections are required, incoming four-wire lines are connected over carrier equipment CE to a hybrid HYB in a voice-frequency relay set, and are connected straight through the relay set by a relay FW if four-wire connections are required. Uniselector TS gives access to a group or groups of four-wire paths OVFRS for transit calls over levels TS1 to TS7 using double-ended wipers, and gives access to two-wire paths LOC for local calls over levels TS8 to TS13 using single-ended wipers connected in pairs displaced by 180 degrees. The paths OVFRS are divided into two groups concerned with remote exchanges or with outgoing relay sets over second selectors. The paths LOC are grouped and have access to a manual board and local second selectors. A receiver 2VFR operates a relay B in response to an incoming V.F. signal seizing the relay set. A digit, comprising a train of pulses each of 2040 c.p.s. operates contact x in receiver 2VFR with each pulse. Relay A responds to each pulse and steps digit switch DS while CD operates and holds up during the pulse train. Terminals DT in level DS2 of the digit switch are strapped to terminal LD or TD according to whether a two-wire or four-wire connection is signified by the received digit. If a two-wire connection is signified, earth is put on terminal LD when CD falls back at the end of the digit and latch magnet LM is energized to start uniselector motor TSDM. Earth extends over rectifier MRA and high-speed test relay T to the contact in level D53 corresponding to the digit, this contact being strapped to contacts in levels TS15 and/or TS16 corresponding to a group os two-wire paths LOC. If a wiper of level TS10 or TS13 finds an idle outlet in the marked group, test relay T responds marking the selected path busy over its upper winding and operating switching relay H in series with latch magnet LM which is in consequence deenergized and stops the uniselector. Relays A and CD may repeat further digits over the path LOC. Reply by the called subscriber operates relay D causing a static modulator SM to transmit a backward signal over the incoming four-wire line by means not described. If the dialled digit registered on switch DS signifies a four-wire connection, earth is applied to terminal TD operating relay TDR and connecting the wiper of level DS3 to the contacts of uniselector level TS14 corresponding to the wanted group of four-wire outlets. If the uniselector finds an idle outlet in level TS6, relay H responds with test relay T and operates relay FW to switch the incoming line straight through to levels TS1 to TS4. Subsequent digits are repeated by contact x of relay 2VFR over level TS6 and a lead SW applies discriminating signals to the outgoing relay set. At the completion of a call relay B is released and switches TS and DS step home.