Patent
1974-09-26
1977-08-30
Griffin, Robert L.
H04B 132
Patent
active
040457419
ABSTRACT:
A tour guide system includes a radio receiver section adapted to receive a plurality of preselected signal frequencies and an automatic frequency selecting means for tuning the receiver only to one of the preselected frequencies whose signal strength exceeds a predetermined amplitude. The receiver section essentially comprises an antenna stage, a tuning stage, a signal amplitude detecting stage, an expander stage, and an audio transducer stage. The automatic frequency selecting means comprises a level detector having an input connected to the output of the receiver detector stage, an astable multivibrator having an input connected to the output of the level detector, a shift register having an input connected to the output of the astable multivibrator and having a plurality of output of each stages, each connected to a field effect transistor (FET) in the tuning stage of the receiver. The tuning stage of the receiver comprises a plurality of capacitors and FET's in parallel with a common inductance. In operation, the astable multivibrator causes the shift register to activate the FET's in such a fashion that the receiver searches for a frequency having a signal strength exceeding a predetermined value. When a frequency is found, the level detector causes the astable multivibrator to cease oscillating, thereby locking the receiver to the predetermined frequency as long as the amplitude of that frequency exceeds the certain predetermined value.
REFERENCES:
patent: 2845599 (1958-07-01), Di Toro et al.
patent: 3497813 (1970-02-01), Gallagher
patent: 3617895 (1971-11-01), Tomsa
patent: 3803495 (1974-04-01), Reynolds
Pulse, Digital & Switching Waveforms - Millman & Taub, pp. 693-695.
"Electronic Switch Using F.E.T." - P. Y. Begasse - IBM Technical Disclosure Bulletin - vol. 13, No. 6 - Nov., 1970, p. 1609.
Bookbinder Marc E.
Griffin Robert L.
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