GB843486A - Improvements in or relating to pulse transmission systems - Google Patents

Abstract

843,486. Automatic exchange circuits. POSTMASTER GENERAL. Sept. 26, 1956 [July 1, 1955], No. 19150/65. Class 40 (4). In a switching arrangement, in which channels are provided with integrating devices which are repeatedly connected together by pulse-operated switches at a rate at least twice the frequency of the signals carried on the channels, arrangements are provided whereby no energy flows. between the integrating devices and the pulse sources themselves. As shown, each of channels A ... C comprises an integrating capacitor CA ... CC whose terminals are connected to a common two-wire channel MP1, MP2 via rectifier pairs WA1, WA2 ... WC1, WC2. Switching pulses if simultaneously applied to the centre taps of coils TAW, TBW cause rectifiers WA1, WA2 and WB1, WB2 to conduct and charge to be exchanged between capacitors CA, CB. Industances LA, LB facilitate complete exchange of the charges. By the symmetry of the arrangement the capacitors cannot interchange energy with the pulse sources. The centre tapped inductance L and resistance R provide a reference potential for the pulses. In the event of one of the pulse sources PC being permanently connected (e.g. in the case of channel C being a junction), then in the event of channel C being connected, say, to channel A, so that the PA pulse is made to coincide with the PC pulse, the presence of the common resistor R causes a reduction in the current supplied from the PC source which reduction may be used as a busy signal for channel C. In an alternative arrangement for use in the case where the circuits belong to two groups, connections only being required between circuits in different groups, the inductance L and resistance R are omitted, the rectifiers of one of the groups are oppositely poled to those of the other two groups, and the pulse sources of this group are made to provide negative-going pulses. Specification 841,555 is referred to.