Patent GB-534023-A (GB)
Title: Improvements in or relating to alternating current signalling systems
IPC: H04Q1/453
Filed: 1939-08-16
Abstract: 534,023. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., WRIGHT, E. P. G., and REYNOLDS, W. J. Aug. 16, 1939, No. 23656. [Class 40 (iv)] In a voice frequency signalling system a prefix signal without which the receiver cannot be operated effectively is sent before each digit with the aid of a regenerator in which the digits are registered on condensers. Specifications 489,545, 489,609 and 489,755 are referred to. Outgoing operation. Relays O, OR are operated over wire 4 when the circuit is seized and are followed by B, BR, RB, CX, which applies an X-frequency calling signal to the junction, CR, BA, which pulls up sluggishly to release CX, CR and terminate the pulse, P and RD. A Y-frequency pulse received from the office ahead to indicate that it is ready for dialling now energizes RY which is followed by G, L and, on the termination of the signal and, consequent relapse of G, LL. Magnet SA now responds to dialled digits, series relay C falling at the end of each to charge a characteristic storage condenser over SAa. At the first step of SA, relay Z, which is nornally energized over wipers of SA, SB in corresponding positions, falls back releasing P, which falls sluggishly, and energizing LD which releases RD. A temporary circuit is thus made for CXY and a burst of X+Y frequency current is sent forward as a prefix signal. On the relapse of P to release CXY and terminate the signal W pulls up and is followed by SD, SE. Relay IG then connects impulse springs ips at their next break to magnet SB of the sending switch and CX in parallel. Relay CX at each impulse projects X frequency current over the junction. When the first charged condenser is reached ZZ pulls up and operates Z and SC pulls up releasing SD, SE to energize P, and release W, Z. LD also falls energizing RD and SC falls back. Relay CXY is energized and P is released to time a prefix signal as in the case of the first digit. When all the digits have been sent the positions of SA, SB correspond and Z remains energized independently of W. Incoming operation. The X-frequency calling signal operates RX which energizes L and at the end of the impulse LL pulls up in the locking circuit of L. Relays IC, ICR, IA pull up and lock and CY sends a burst of Y-frequency current over the junction and energizes CR. Relays B, BR, RB also are energized and later BA which terminates the Y-frequency pulse and allows RD to operate in the holding current of RB. In response to the mixed X + Y frequency prefix, RX, RY remove a shunt from RG which energizes RC. Relay RG is thus short circuited and RB, RD are disconnected, RD takes 110 milliseconds to fall and then disconnects the junction from the speech current. RB takes 220 milliseconds to release. If it has fallen when the termination of the signal releases RX, RY a circuit is made for RE. RC remains operated until the end of the digit. RX repeats the numerical impulses to AKA which repeats them over circuit 14. When non-signal frequencies are received, GA disables the signal receiver by locking itself, RB and RD until the relapse of RC when the line has been clear of signal frequencies for a definite time.