Patent GB-374959-A (GB)
Title: Telephone systems with repeaters
IPC: H04Q1/30
Filed: 1931-03-20
Abstract: 374,959. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. and SKILLMAN, T. S., Connaught House, Aldwych, London. March 20, 1931, No. 8660. [Class 40 (iv).] Wanted numbers are sent over repeatered lines in a form, e.g. voice-frequency combinations or dialled voice-frequency impulses, which passes through the repeaters while supervisory signals, or certain of them, comprise direct current signals byepassed by relays at the repeaters. The cathode circuits of the repeaters are completed by the relays. Fig. 1 shows a four-wire circuit with terminal and intermediate repeaters 3, 4, 5 each having a byepassing circuit 7.. 11. The left-hand end is shown in detail for semi-automatic operation n Fig. 3, although this end may be seized by a selector in full automatic operation. When the operator plugs in, sleeve relay B completes the cathode circuits of the two repeaters 3, 5 and connects battery and ground over relay C to the outgoing side of repeater 3 to operate a relay on the incoming side of the intermediate repeater which similarly connects battery and ground to the outgoing side to operate a relay on the incoming side of the distant terminal repeater. The relay at the distant repeater associates automatic equipment including a register (not shown) with the line, and a supervisory signal passed back over the other path in a similar manner operates relay A, Fig. 3, to reduce the resistance of the sleeve circuit and operate a marginal relay which extinguishes the supervisory lamp. Modified relay arrangements for two-wire circuits are shown in Figs. 5 and 6 in connection with intermediate repeaters. In Fig. 5 the signal is passed on in the forward direction by relays L, J and in the reverse direction by relays H, K. In Fig. 6 the forward signal is passed on by relay N over M which is marginal and does not operate. The backward signal comprises a reduction of resistance which operates M to short-circuit one winding of N. Fig. 6 is a one-way circuit only. The operator sends out the number and when the automatic switches have been set and the register released, a signal is sent back to light the lamp to inform the operator that she may ring. The ringing signal may be (1) momentary interruption of the D.C. signalling circuit relayed as described above, and causing the automatic equipment to send out ringing current, (2) voice-frequency current from the cord-circuit passing to the distant receiving equipment, or (3) voicefrequency current from the cord-circuit to special auxiliary receiving equipment 25, Fig. 7, at the distant end which was connected up when the operator seized the line and is released on reply of calling party. The equipment 25 may also be used to receive signals of voicefrequency combinations for transferring the call to an operator, breaking into or breaking down a local connection and for re-ringing a called party, the equipment 25 being reconnected in the last-mentioned case, when the called party hangs up. In full automatic working, the calling party sets a register at the outgoing end and voice-frequency equipment is provided, in the register or otherwise, to respond to backward signals indicating the state of the call, e.g. to delay digit transmission after the first digit until further incoming equipment is ready, particularly on tandem connections. Specification 350,900 is referred to.