Noise detector for frequency modulation systems
AssigneeBell Telephone Laboratories, Incorporated
InventorsJohn R. Celli, Donald H. Nash
Life of this patent
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Abstract
A hands-free telephone system is disclosed utilizing an infrared transmitter and receiver to permit wireless speech transmission. The transmitter uses frequency modulation imposed on the infrared signal and includes carrier shift signaling arrangements for indicating a low battery condition and transmitter turn-off. The receiver utilizes a noise detection circuit for permitting remote turn-on, for squelching noise in the voice path, and for feeding an alerting signal to a loudspeaker to indicate that the received signal is excessively noisy. The portable transmitter must then be moved or redirected to provide a better line-of-sight signaling path.
Claims10
A noise detector for a frequency modulated transmission system
- characterized by
- a phase-locked loop adapted to track the modulating signals of frequency modulated signals received in said transmission system,
- an exclusive OR circuit,
- means for applying said frequency modulated signals to said phase-locked loop and to said exclusive OR circuit, and
- means for integrating the output of said exclusive OR circuit.
A hands-free telephone station system using frequency modulated carrier transmission between a portable transmitter and a stationary receiver
- characterized by
- a phase-locked loop adapted to track said frequency modulated carrier signals, and
- means including an anticoincidence circuit for comparing the phase of said frequency modulated carrier signal and the output of said phase-locked loop.
Dependencies are inferred from the claim text.