GB267181A - Improvements in or relating to telephone systems - Google Patents

Abstract

267,181. Standard Telephones & Cables, Ltd., (Turkhud, B. A., and Fremery, F. de). Nov. 3, 1925. Automatic and semi-automatic exchange systems.- In phantom circuit systems such as that described in Specification 261,103, a single impulse circuit is provided for a number of speaking circuits. As shown, the four pairs L1 - - L4 provide six talking channels terminating in trunk circuits such as that shown in Fig. 2. The seventh channel or " ghost circuit " is connected at one end to an impulse transmitter D and at the other to a thermionic valve controlling a repeating relay F. The impulse circuit is associated with a particular channel by sending a preliminary impulse of ring- ing current over the channel whereupon relay A pulls up, locks itself and causes energization of relays B, C, C<1>, D, D', L. Relay D<1> cuts off relays A, B, and relay L connects the incoming end of the ghost circuit to the grid of the repeating valve. Relay C lights the valve filament whereupon relays F, F<1>, G, N pull up. When the dial is operated the loop, over which the grid is normally grounded, is cut and battery is connected to the grid via the upper half of the ghost circuit for each impulse. Relay F repeats the impulses to the switches. Relay G which is slow to operate falls back at the beginning and pulls up again at the end of each train and with relay N builds up the counting chain. When the full number of digits has been sent, relay Scr 6 energizes relay H which locks up and energizes relay J which releases relays C, C<1>, D, D<1>, L &c. The connection is released by sending a further impulse of ringing current over the talking circuit.