Squelch system for use in a multiple carrier AM communications systems receiver

摘要

A squelch system for use in a multicarrier communications receiver includes a conventional noise squelch circuit having a detector and filter operative to close a squelch gate in the absence of an incoming carrier and a phase locked loop means parallel thereto. The phase locked loop means does not lock onto noise signals but will lock onto carrier difference signals within its frequency range to open the squelch gate. A further improvement to the squelch system uses a threshold switch which parallels the above-mentioned conventional squelch circuit and phase locked loop means and comprised of a low pass filter and a comparator to maintain the squelch gate closed until the carrier portion of the receiver AM audio signal is above a certain threshold.