Patent
1976-03-04
1977-06-07
Cooper, William C.
H04M 150
Patent
active
040285014
ABSTRACT:
A multiple frequency signalling receiver translates combinations of tone signals received from a telephone set to derive binary two out of eight coded signalling. Received signals are directed by a filter to high and low band translator circuits. Each translator circuit includes a circuit for deriving a threshold signal from the received signal and a threshold signal controlled limiter for limiting the received signal. The threshold signals are cross coupled between the limiter in each translator to prevent response to signals in the high and low bands being substantially unbalanced in amplitude. Digital counting and decoding circuits in each translator circuit detect predetermined frequencies of signals from the limiting circuits. Upon occurrence of a consistent detection by both the translator circuits lasting for at least about 40 milliseconds, the appropriate two out of eight code is gated to the output terminals of the multifrequency receiver. Tolerance to subscriber loop noise is enhanced with the addition of latch timer circuits in series with the outputs of the decoder circuits, whereby short interruptions in the tone signals are ignored.
REFERENCES:
patent: 3537001 (1970-10-01), Friend
patent: 3790720 (1974-02-01), Schartmann
patent: 3795775 (1974-03-01), Cowpland
patent: 3914557 (1975-10-01), O'Neill
Cooper William C.
Northern Electric Company Limited
Popek Joseph
Turpin Frank
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