Arrangement for and method of detecting multi-frequency sound co

Details Arrangement for and method of detecting multi-frequency sound co Arrangement for and method of detecting multi-frequency sound co

1982-12-23

1984-10-23

Griffin, Robert L.

Pulse or digital communications

Repeaters

Testing

34082574, 364827, H04L 506

Patent

active

044792298

ABSTRACT:
A multi-frequency signal receiver for use in telephony signalling systems comprises a plurality of frequency selective circuits whose outputs are connected to a signal combination detector which produces a code at its output which depends on the signals passed by the frequency selective circuits.
A guard circuit is provided to inhibit the output of the signal combination detector. The guard circuit determines the total received power and compares this with the power of two strongest multi-frequency signals received in order to decide whether the detected signal is valid. The guard circuit also includes a comb filter having maximum attenuation at the frequencies to which the frequency selective circuits are sensitive and minimum attenuation half way between the frequencies to which two successive frequency selective circuits are tuned. If the power passed by the comb filter is greater than a predetermined value the output of the signal combination detector is inhibited. This prevents a single frequency large amplitude signal located mid way between two successive signalling frequencies from activating the receiver.

REFERENCES:
patent: 3104393 (1963-09-01), Vogelman
patent: 3710257 (1973-01-01), Low et al.
patent: 3810019 (1974-05-01), Miller

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