GB759645A - A telephone system with linefinders - Google Patents

Abstract

759,645. Automatic exchange systems. LICENTIA PATENT-VERWALTUNGS-GES. April 27, 1954 [April 27, 1953], No. 12120/54. Class 40 (4). In a system in which a line-finder tests over the calling subscriber's loop, the line-finder connects into the test circuit a resistance-condenser combination to prevent rapid build-up of charge in the bell condensers of idle subscribers, which would otherwise cause unwanted tinkling of the bell. The satellite exchange shown has no batteries of its own and is provided with three main exchange lines VL<1>. . . VL<3> to which access is obtained over relay selectors, only the control circuit RW<1> of the first being shown. Battery is normally connected at the main exchange to both legs of VL<1> so that A and B are normally operated. When a subscriber T<1> closes his loop, a chain circuit is completed over the wire An for the relay D in the control circuit (say RW<1>) associated with the first free exchange line, to battery over the b-leg of VL<1>. Relay D disconnects A from the a-leg of VL<1> so connecting the selector control circuit to the a-leg. The main exchange then supplies pulses to the circuit RW<1> to step the relay switch, the testing circuit over the lead Pr being connected up by D which also connects up the resistance-condenser circuit C<1>, W<1>, W<2> in parallel with the subscriber's line circuits. The condenser C<1> in series with the resistor W<1> reduces the rate of rise of potential in each subscriber's line circuit. The condenser discharges over W<2> between each step. Completion of the connection takes place in known manner. Specification 759,589 is referred to.