Telecommunications – Receiver or analog modulated signal frequency converter – Frequency or phase modulation
Patent
1997-07-29
2000-04-04
Chin, Wellington
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency or phase modulation
455222, 455218, 455219, 331 16, 381 15, H04B 110
Patent
active
060471700
ABSTRACT:
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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Gilbert William C.
Paulsen Roger L.
Semwayo Colin
Chin Wellington
Honeywell Inc.
Jama Isaak R.
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