Patent GB-561364-A (GB)
Title: Telephone systems
IPC: H04Q3/00
Filed: 1942-06-11
Abstract: 561,364. Semi-automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. June 11, 1942, No. 7983. Convention date, April 23, 1941. [Class 40 (iv)] In a system in which connections between toll offices are set up by operators over two-way junctions, all the signals over junctions, including dialling impulses, consist of two audiofrequencies in succession, and cut-off relays are provided under control of the sending and receiving circuits for isolating the junction at each end while signalling is in progress. A junction T12 terminates at a first toll office in a toll line circuit TLC1, Fig. 4, which includes a signal transmitter ST1 and signal receiver SRI, Fig. 5, and which is connected through a two-way circuit TWT1, Fig. 3, to outgoing and incoming circuits OT1, Fig. 1, and 1T1, Fig. 2. At a tandem office it terminates in a toll line circuit TLC2, Fig. 6, which includes a signal transmitter ST2 and signal receiver SR2, Fig. 7, and is connected through a two-way circuit TWT2, Fig. 8, to an outgoing circuit OT2, Fig. 9, and a route selector, Fig. 8. The latter gives access to incoming circuits 1T2, Fig. 10, and to junctions to other toll offices which are equipped like the junction T12. Seizure of junction.-When the operator at the first office plugs into jack J2, sleeve relay 1A connects up 1D, 3B and 1Q energizes over the tip and through 1P connects 1T to the ring. Pad-control relav 4L is released and connected through 1H, 1R to wires 161, 162. The operation of 1T connects up relays 4H, 4J, 4K of the transmitter ST1 to send a seizure signal. Relay 4H connects up sluggish relay 4E and releases cut-off relay 4D, while 4J applies frequency f1 to the junction over repeating coils 429, 400. Relay 4K connects up 4G and disconnects 4C which releases after condenser 439 has charged and connects up 4A. Frequency f2 is now substituted for f1 and continues until the relapse of 4B which is delayed by the charging of condenser 442. The signal is then terminated and 4D reoperates. At the tandem office the signal passes through coil 620 to the receiver SR2 in which relays 7J, 7K respond to frequencies f1, f2, which are detected by a pair of tuned circuits 730, 740 fed by a peak-limiting amplifier 725 and control sluggish relays 7L, 7N. While 7L is still up, 7K connects up 7P, which releases cut-off relay 6C, and 7M which operates 7C. The latter connects up sluggish relay 7F and makes a circuit for 7A over wire 970 in series with 8G which extends wires 961, 962 to the selector TS2 and connects impulse relay 8E through 8C to wire 970. Sluggish relay 8D energizes, holds 8G and grounds wire 853 to operate 7B. Relay 9Q lights busy lamp L9 and releases pad-control relay 6B. At the end of the signal, the release of 7P reoperates 6C. Dialling.-Dialled. impulses are repeated by 1T to relavs 4H, 4J, 4K. The release of 4H connects up sluggish relay 4F which holds open the circuit of cut-off relay 4D until the end of the train, while the release of 4K operates 4B to apply frequency f2 and disconnects 4G which falls back after condenser 436 has charged and re-operates 4C, so that 4A relapses and substitutes frequency f1. The re-operation of 4K at the end of the impulse causes 4A to pull up again and replace frequency f2. After the last impulse of the train, frequency f2 continues until 4B restores, and 4D re-operates when 4F falls back. Should dialling start before the seizure signal is finished, 4B holds and frequency f2 continues as part of the first impulse. At the receiver SR2, since frequency f1 follows frequency f2, 7Q energizes instead of 7M and connects up 7H which disconnects 7E. The latter falls back after condenser 771 has charged and releases 7C which opens the circuit over wire 970. When frequency f ends, 7H falls back after condenser 798 has charged and re-operates 7E, 7C. Relay 7P which controls 6C is maintained until frequency f2 is removed at the end of the train. The selector TS2 operates in response to impulses over wire 970 and selects an idle trunk, to which wires 961, 962 are extended by switching relay 8L. If no idle trunk is found, an interrupter is connected to 8B to cause the repeated transmission of signals, as described below, to flash the supervisory lamp. Answering of call at tandem office, and supervisory signalling.-If the selected trunk leads to the incoming circuit 1T2, relay 10A energizes in series with 7A, 8C and lights calling lamp L10, ringing tone being returned to the first office. When the operator plugs in, sleeve relay 10K connects up 10G which locks under the control of 10B and operates 8B to send a reply signal. Relays 6D, 6E, 6F of the transmitter ST2 energize over wires 964, 965, 966 to send frequency f 3 followed by frequency f4, as in the transmitter ST1. Relays 5E, 5A respond in the receiver SR1, and, as in the receiver SR2, bring about the operation of 5L to close a circuit for 5P over wire 170 in series with 1B which disconnects the low-resistance winding of 1A to darken the supervisory lamp. The return of the dialling key restores 1Q and operates switching relay 1K. While the answering operator's set is connected, battery on the tip and ring energizes 10M, 10L to unbalance the simplex circuit on wires 1001, 1002 and operate 9G which causes the insertion of pads P61, P62 in the toll line circuit TLC2, these having been previously removed by the operation of 9Q. When the call is extended, 10M may be held or not according to the nature of the outgoing trunk. If resistances 921, 922 are such as to unbalance the aforesaid simplex circuit, 10C, 10J are operative to disconnect 10M and feed forward battery to hold the pad relay of the outgoing trunk. If the answering operator unplugs, 8B is disconnected and the release of 6D, 6E, 6F sends back a signal comprising frequency f4 followed by frequency f3. The receipt of this signal at the first office causes the release of 5L and hence of 1B, which lights the supervisory lamp. The answering operator may be recalled by actuation of the ringing key, which connects battery to the tip to operate 1H. Relay 1E energizes and on its relapse when the key is restored disconnects IT momentarily to send a signal like a single dialled impulse. This is repeated over wire 970 at the tandem office to 10A which causes the flashing of the supervisory lamp by the connection of an interrupter to 10F. In a similar way, actuation of the ringing key by the answering operator energizes and releases 10E which controls 8B to send a signal comprising frequency f4 followed by frequency f3. This as before causes the release of 5L, 1B to light the supervisory lamp. It is to be noted that at the receiver SR1 relay 5Q (corresponding to 7B) is inoperative on an outgoing call and therefor 5M follows 5K and operates 5J by the successive discharge of condensers 582, 581 to delay the re-operation of cut-off relay 4D for about ¢ sec. after the signal ends. When the calling operator unplugs, the release of 1T initiates a disconnect signal comprising frequency f2 followed by frequency f1, the latter continuing until both 4E and 4F are back. The release of 7C opens the circuit of 7A, 8C, 10A, and since frequency f continues sluggish relays 7F, 8D also fall back, and the latter releases 8L, 8G to restore the selector TS2 and the two-way circuit TWT2. Relay 10A connects up 10B to light the supervisory lamp, and the relapse of 10G grounds wire 1003 to prevent reseizure of the incoming circuit 1T2 until the operator unplugs. Connection to a third toll office.-The selector TS2 selects an outgoing junction and ground on wire 823 is extended to operate a relay like 8H in the two-way circuit associated therewith, while the circuit through 7A, 8C is extended to a relay like 8A, which causes the transmission of a seizure signal to the third office. The receipt of an answering signal over this junction completes a circuit over wire 1824 for 8B, which repeats the signal to the first office. Subsequent signals are repeated in the same way, and the disconnect signal from the first office is also effective to control release at the tandem office. It may be noted that the cut-off relays are not released until the second frequency of an incoming signal has begun to arrive. The delayed operation of certain relays in the signal receivers, however, prevents any false operation which might result from a signal passing directly through a tandem office.