Decoder for frequency-modulated tones of two different lengths

Details Decoder for frequency-modulated tones of two different lengths Decoder for frequency-modulated tones of two different lengths

1976-05-14

1977-05-17

Griffin, Robert L.

Communications: radio wave antennas

Antennas

Balanced doublet - centerfed

325395, 343228, H04B 106

Patent

active

040244750

ABSTRACT:
A frequency recognition circuit includes a first phase locked loop to detect the carrier tone frequency, which locks to the detected frequency and provides the frequency-modulation frequency to a second PLL for modulation frequency recognition. When the predetermined carrier and modulation frequencies are recognized, an AND-gate provides a signal that removes a short-circuit from a capacitor that then begins to charge through a time constant circuit. The time constant circuit triggers a threshold switch after a period determined as the minimum duration for a signal and the threshold switch operates to advance a flipflop which performs a switching function and, at the same time, changes the time constant circuit so that the threshold switch will operate the next time on a signal of a different minimum duration. The decoder is designed to switch the output of a radio receiver on and off for selectively listening to traffic announcements.

REFERENCES:
patent: 3628153 (1971-12-01), Fukata
patent: 3657655 (1972-04-01), Fukata
patent: 3755744 (1973-08-01), Fukata
patent: 3792199 (1974-02-01), Saeki
patent: 3921076 (1975-11-01), Currie
patent: 3922607 (1975-11-01), Wysong
patent: 3949401 (1976-04-01), Hegeler
patent: 3995220 (1976-11-01), Hansen

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