GB355691A - Improvements in or relating to electrical signalling systems - Google Patents

Abstract

355,691. Signalling on telephone circuits. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, SMITH, J., 9, Merivale Street, Durning Road, both in Liverpool, and TURTON, G. D., Warden House, Greenwich, Ripley, near Derby. May 26, 1930, No. 16229. [Class 40 (iv).] In a system for signalling over a two-wire conductor, including valve repeaters, the signal is transmitted by a predetermined number of pulses of audio frequency within the voice frequency range, the pulses being transmitted under control of a timing device. To ring over the line 12, 13, ringing current is received over 10, 11, operating RR, and relay A operates and locks to 1a of CS. Relay C energizes and B pulls up. Relay C connects current of 500 frequency to the line 12, 13 and also energizes magnet CSM. Relay B breaks the circuit of C and, after a slow release pause, C falls away releasing CSM and opening the line circuit. Slow relays B and C interact connecting pulses to line and stepping CS. When 10 pulses have been sent, 1a leaves the commoning and A releases, breaking the circuit of C and allowing CS to home. At the receiving end the pulses pass via filter FC to the valve amplifier VAC and energize relay E. The pulses are thus repeated to F and, as G locks up for the impulse train, switch RS is stepped. When the ten pulses have been received, CR energizes and locks over 14 to contacts of a reply relay, connecting ringing current to the conductors 15, 16. Relay G relapses and switch RS returns to its home position. If during speech the ringing frequency is received, relay F will respond, energizing G and moving switch RS. The receipt of 10 impulses of the selected frequency at the correct time spacing is however almost impossible, and G will relapse before CR is energized allowing RS to return to normal.