Audio frequency signalling systems for telephone systems

Details Audio frequency signalling systems for telephone systems Audio frequency signalling systems for telephone systems

1975-02-10

1976-10-12

Claffy, Kathleen H.

Amplifiers

Signal feedback

Combined with control of bias voltage of signal amplifier

179 1A, 179 84T, 330 52, H04M 160

Patent

active

039859762

ABSTRACT:
Audio frequency signalling, from a central location in a telephone system to a remote location serviced by a particular telephone set, is accomplished by connecting an audio frequency amplifier, having a predetermined a.c. threshold voltage level, and a predetermined d.c. voltage level, across the telephone line at said particular telephone set. By concurrently applying a low frequency a.c. pilot signal of an amplitude greater than the a.c. threshold voltage level of the audio frequency amplifier and an audio frequency signal voltage of a lesser amplitude to the telephone line at the central location, when said particular telephone set is on-hook, said audio frequency amplifier is enabled by the low frequency a.c. pilot signal and supplied with operating current from the telephone line. The audio frequency amplifier, thus enabled and energized, attenuates the low frequency a.c. pilot signal and amplifies the audio frequency signal voltage to produce a corresponding audible signal at a loudspeaker coupled to said audio frequency amplifier. When the handset of said particular telephone set is taken off-hook the d.c. voltage across the telephone line at said particular telephone set drops below the predetermined d.c. threshold voltage level to disable said audio frequency amplifier.

REFERENCES:
patent: 2824174 (1958-02-01), Holman
patent: 2824175 (1958-02-01), Meacham et al.
patent: 3501648 (1970-03-01), Chapman et al.
patent: 3671676 (1972-06-01), Henry et al.
patent: 3899644 (1975-08-01), Hunt

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