Signalling and channel loop test circuit for station carrier...

Details Signalling and channel loop test circuit for station carrier... Signalling and channel loop test circuit for station carrier...

H - Electricity

04

J

329/3, 325/30, 3

H04J 1/14 (2006.01)

Patent

CA 1169982

Attorney's Docket No. TII-78/78/369 ABSTRACT OF THE DISCLOSURE A plural channel amplitude modulated station carrier telephone system and method wherein two a.c. signals are applied to modulate a called subscriber's channel carrier signal at a central office to signal an incoming call for the subscriber, wherein a phase locked loop is used at the subscriber terminal equipment to lock with one of the two a.c. signals following recovery of the two a.c. signals from the called subscriber's carrier signal, wherein the output of the phase locked loop is utilized to provide for the synchronous detection of the other of the two a.c. signals, and wherein a ring circuit responds to thesynchronous detection of the other of the two a.c. signals to ring the called subscriber's telephone. According to another feature of this invention, the a.c. signal to be synchronously detected is interrupted at a rate determined by and equal to the central office ringing signal frequency, and the thusly interrupted synchronously detected a.c. signal is filtered at the subscriber terminal to develop a local ringing signal voltage having the same frequency as the central office ringing frequency. According to another feature of this invention the signal with which the phase locked loop is locked is utilized to perform a channel loop test on any selected channel in the carrier system. Other features of this invention include a ring circuit with either a special transistor switching or relay switching arrangement to develop the voltage that is applied to operate the ringer in the subscriber's telephone. Also disclosed is a novel synchronous detection circuit which employs a special phase locked loop for synchronously detecting an a.c. signal.

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