Honeywell G.m.b.h.

Colin Semwayo

William C Gilbert

Roger L Paulsen

An improved squelch circuit which utilizes a phase-locked-loop (PLL) arrangement to track the carrier signal and identify when audio communication should be curtailed. The lock detect circuit of the PLL is used for a signal-to-noise monitor. As the loop locks and unlocks, the lock detect line pulses. These pulses are integrated to give a direct current (DC) level. This DC level is proportional to the signal-to-noise ratio of the carrier signal. The signal-to-noise level is monitored by the squelch gate until a threshold is passed. Falling below the threshold results in a squelching of the audio, when the ratio exceeds the threshold, then audio is commenced. The circuit is enhanced by the ability to automatically adjust the threshold level once the PLL has locked onto the signal. Further, in some embodiments of the invention, the PLL also adjusts its bandwidth if the receiver's bandwidth is changed, thereby allowing the PLL to monitor the signal and not open and close the squelch intermittently when the signal strength is only marginal.

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Phoenix, AZ, United States of America

Colin Semwayo