GB346790A - Improvements in or relating to telephone systems - Google Patents

Abstract

346,790. Manual exchange systems. STANDARD TELEPHONES & CABLES, Ltd., SKILLMAN, T. S., and FREETH, L. G., Columbia House, Aldwych, London. Jan. 17, 1930, No. 1784. [Class 40 (iv).] A call indicator is controlled over a two-way international junction by voice-frequency currents, a single impulse comprising one or more of four frequencies being used for each digit. Prior to sending a number, the operator momentarily operates PK to send a comparatively long ZY impulse timed by DC and so release EA at the incoming end. This may cause a call indicator to associate itself with the junction, but in the system shown in which there is only one junction to a call indicator, energizes EB, releases any operated storage relays, homes DS if necessary and holds its magnet SH energized in normal position so that at the end of the impulse it connects up the first storage group. The digit keys send short impulses timed by DE, DD. EC which is operated by any received signal, energizes or holds EB, and energizes SM to cause DS to move on after each impulse. EB energizes DD, Fig. 1, to prevent interference by keying by the incoming operator. She can break in however by transmitting ringing current to AF which energizes V, R to send an XZ pulse, releasing N at the outgoing end and so causing ringing current to be connected to the cord to operate a calling lamp. As shown the keyset is connected to the cord by the ringing key but it may be connected by the talking key. The function performed by PK may be taken by a special preparing button associated with the keystrip. A further button may be provided for sending a special signal to indicate an intention to send a succession of calls (the normal arrangement being that each call is followed by one in the opposite direction), by releasing a relay like EA.