How did you implement this in a receiver which wasn't equipped with hysteresis squelch? I have a couple R-5000s whose AM/FM squelch absolutely sucks.
For the R5000 FM squelch, that usually also are used as a squelch in AM mode, it takes the audio at the left part of the schematic and filter it to only use the higher frequencies of the audio where no speech frequencies are present and then turn it into a positive DC voltage.
That IC7 has 3.6 volt at its negative input, and that voltage change with the squelch knob, with a full carrier without any noise but when the noise level increase that 3.6V will increase above 4.3V that are the voltage at its + input and will switch its output to negative that will mute the audio. That R223 will force the 4.3V + input voltage to go more negative, making the difference to the - input even greater requiring the - signal to drop even more, a less noisy signal, until it will switch its output again that makes the hysteres level.
Making R223 lower in value, maybe 1.8M will create a bigger distance between open and close of the squelch. Reducing R251 in value will create less hysteres and bridging it to 0 ohm will be no hysteres at all. Replacing that 2.2k R251 with a 33k potentiometer will make it possible to adjust the hysteres to your liking for different modulation modes. There's a VR3 trim pot at 33k for SSB mode to match SSB squelch hysteres to the AM/FM squelch.
It already have a hysteres using that R223 but high ohm resistors have a tendency of going even higher in value if they are very old and will then loose the hysteres function in this squelch circuit.
/Ubbe
