1974-11-06
1976-06-08
Safourek, Benedict V.
325 64, 328138, H04B 116
Patent
active
039626458
ABSTRACT:
In some radio communication systems, a tone of selected frequency (usually below the voice frequency) is transmitted so as to activate only selected radio receivers in the system. Each of such radio receivers is provided with a circuit for detecting a selected tone frequency. The detecting circuit includes means for producing sequences of pulses at a rate N times higher than the selected tone frequency, so that each sequence contains one through N numbered pulses for each cycle of tone. A selected portion of each cycle of tone of desired frequency coincides with the same pulses of each sequence, and these coincidences produce vectors of the same angular phase (corresponding to the pulse numbers). If the sum of a plurality of such vector outputs exceeds a certain threshold level, an output signal is produced to indicate that the proper tone frequency is received, and this output signal can activate the receiver. The selected portion of each cycle of tone of undesired frequency causes coincidences with different pulse numbers in each sequence, and these coincidences produce vectors of different phases, so that the vector sum does not reach the needed threshold level for receiver activation.
REFERENCES:
patent: 3537001 (1970-10-01), Friend
patent: 3578919 (1971-05-01), O'Neill
patent: 3633112 (1972-01-01), Anderson
patent: 3684965 (1972-08-01), Gautney et al.
Bookbinder Marc E.
General Electric Company
Safourek Benedict V.
Williams James J.
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