GB647597A - Telecommunication exchange - Google Patents

Abstract

647,597. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. April 2, 1948, No. 9309. Convention date, April 26, 1947. [Class 40 (iv)] An exchange system similar to that described in Specification 644,571 is supplied with electronically-controlled ringing. Incoming pulses from a calling subscriber connected to the distributer 1, seize a line-finder (top half of Fig. 2) which thereupon opens the gate 18 at the calling subscriber's time position to pass-pulses over wire 23 to the dial impulse circuit. Dial impulses received thereby set the register, Fig. 3, so that it produces pulses, which are applied to the input, output and ringing gates 18, 19 and 43, respectively, at the called subscriber's time position. Valves 36, 37 change over during the impulse train after which they restore, thereby changing over valves 39, 40 to close the dial gate 27 and open the ringing gate 43. The ringing signal is thereby transmitted from oscillator 45 to the called substation to actuate a cold cathode discharge relay therein to operate an audible or visual signal. When the called subscriber answers pulses so produced on wire 48 coincide with those derived from the register, thereby causing valve 49 to produce negative pulses to restore valves 39, 40 and cut off the ringing current. The resulting 'pulse from valve 40 changes over valves 52, 53, thereby biassing the output gate 19 so that it conducts on receiving pulses either from the register or the line-finder. Speech then passes in both directions between the anode of the distributer 1, input gate 18, storage filter 65, output gate 19 and the grid of the distributer 1. When the calling subscriber hangs up a pulse from the line-finder over wire 72 restores the register, the valves 52, 53 and if necessary valves 39, 40.