Signalling in pbx systems

Details Signalling in pbx systems Signalling in pbx systems

H - Electricity

04

M

379/3

H04M 11/00 (2006.01) H04L 25/49 (2006.01) H04M 9/00 (2006.01)

Patent

CA 1185024

ABSTRACT OF THE INVENTION "SIGNALLING IN PBX SYSTEMS" The exchange ZSt is star-connected to the telephones TSl to TSx via four-wire subscriber lines each comprising a signalling wire-Pair c, d used for two-way alternate digital data transmission. This data transmission is by line voltage variation in one direction (ZSt to TS)and by line current variation in the other direction. To inhibit noise on the speech wire-pair a, b a sending unit Sz has a reactive circuit R1, Cl, R2, R3, C2 to deform rectangular pulses whose harmonics are normally bad from the point of view of noise. Since this deformantion tends to introduce phase shifts, a receiving circuit Ez corresponding to the one Et used at the receiving end (TS) detects the transmitted pulses and provides synchronising signals for a control unit Pz which synchronises an oscillator Oszl with the receiving end oscillator Osz2. (Fig. 1)

386626

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