Apparatus and method for detecting the onset of a frequency shif

Details Apparatus and method for detecting the onset of a frequency shif Apparatus and method for detecting the onset of a frequency shif

1982-01-20

1983-12-27

Safourek, Benedict V.

Pulse or digital communications

Repeaters

Testing

324 78F, 324 78Q, 328138, 329145, H03D 306

Patent

active

044235194

ABSTRACT:
An incoming signal is tested for the presence or onset of a frequency shift keyed (FSK) signal which alternates at a known rate between two unknown frequencies separated by a known frequency shift. The incoming signal is time delayed an odd multiple of the keying period and the delayed signal is multiplied by the incoming signal to produce sum and difference frequencies when the FSK signal is present. The difference frequency is selected by filtration, demodulated and integrated to produce a useable detector signal. The detector signal is compared with a threshold signal which is generated to discriminate between the FSK signal and other unwanted signals or noise in the communication channel.

REFERENCES:
patent: 3189820 (1965-06-01), Lowman
patent: 3636446 (1972-01-01), Genter
patent: 4072931 (1978-02-01), Davis
patent: 4121165 (1978-10-01), Dogliotti et al.
patent: 4250453 (1981-02-01), Nilsson

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