1977-07-26
1978-05-23
Claffy, Kathleen H.
H04M 150
Patent
active
040912434
ABSTRACT:
Detection of valid two-out of-N multifrequency signals is realized by employing a microprocessor in conjunction with a controllably adjustable or settable reference threshold level and a plurality of threshold detectors. Under control of the processor, a reference threshold level supplied to the detectors is set to a first prescribed level. Upon detection of a tone which exceeds the first threshold level the processor controllably sets the reference threshold level to a second prescribed level. Detection of two, and only two, tones which are present for at least a minimum prescribed interval are then considered valid.
REFERENCES:
patent: 4016370 (1977-04-01), Laoteppitaks et al.
Mizrahi Albert
Moyer Neal John
Pezzutti David August
Bell Telephone Laboratories Incorporated
Claffy Kathleen H.
Popek Joseph A.
Stafford Thomas
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