Telecommunications – Transmitter and receiver at separate stations
Patent
1985-12-20
1988-11-08
Griffin, Robert L.
Telecommunications
Transmitter and receiver at separate stations
455221, 375104, 34082548, H04Q 700, H04B 100
Patent
active
047838450
ABSTRACT:
A digital tone squelch detect circuit functions to give an enabling signal for audio transmission in an FM radio network. The circuit comprises an analog to digital converter which outputs a binary coded signal representative of the voltage level of a received audio tone signal. The binary signal is then placed into a shift register which periodically is rotated and multiplied by a reference clock signal for correlation with a stored replica of the tone. The output of the correlator, which is representative of the degree of correlation, is fed to an accumulator which integrates it and sends it to a comparator where its binary valve is compared to an arbitrary threshold binary value by a hysteresis network. After detection the hysteresis established circuit outputs a tone detect signal and lowers the detection threshold so as to maintain the tone detect signal during periods of signal fadeout. However, if no signal is detected for several cycles, the threshold is raised to the previous binary level so as to avoid triggering on noise.
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Cook Michael W.
McChesney James R.
Griffin Robert L.
ITT Aerospace Optical
Kuntz Curtis
Twomey Thomas N.
Walsh Robert A.
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