Telephone ringing detectors

Abstract

A telephone ringing signal detector is disclosed for detecting four-party fully selective superimposed ringing signals on a telephone line. Detecting these signals at the central office end of a subscriber loop carrier system permits encoding the ringing signals for transmission on the carrier system and subsequent decoding and utilization at a remote carrier terminal to control the regeneration of selective ringing signals. The ringing detector includes separate 20 Hz alternating current signal detectors for each conductor of the telephone pair and further includes separate polarity detector for each conductor. The polarity signals for the two conductors are gated by the outputs of the respective 20 Hz signals and combined in a single polarity indication applicable for either conductor. False signaling indications are thereby prevented in the presence of central office variations of amplitude, waveform and level of the dc signals, as well as variations in the phase of the ringing signals.

Dependencies are inferred from the claim text.