H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/2
H04M 3/08 (2006.01) H04Q 1/457 (2006.01) H04Q 1/46 (2006.01)
Patent
CA 1193773
ABSTRACT: A multi-frequency signal receiver for use in telephony signalling systems comprises a plurality of frequency selective circuits (2-7) whosa outputs are con- nected to a signal combination detector (8) which produces a code at its output (9) which depends on the signals passed by the frequency selective circuits (2-7). A guard circuit (10) is provided to inhibit the output (9) of the signal combination detector (8). The guard circuit (10) 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 (10 also includes a comb filter having maximum attenuation at the frequencies to which the frequency selective cir- cuits (2-7) are sensitive and minimum attenuation half way between the frequencies to which two successive frequency selective circuits are tune. If the power passed by the comb filter is greater than a predetermined value the output of the signal combination detector (8) is inhibited. This prevents a single frequency large amplitude signal located mid way between two successive signalling frequencies from activating the receiver.
418965
Wolters Gerardus A.m.
N.v. Philips Gloeilampenfabrieken
Van Steinburg C.e.
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