A quickie on how the maggiore squelch circuit "works". (when/if it
decides to.)
The five transistor chip is the heart of it, but not all of it.
The first transistor is just a linear amplifier.
The second is biased class C, and interacts a bit with the third.
The third is a little interesting, I'll come back to it.
The fourth provides COR output, which is faster than the audio mute.
The fifth mutes the speaker locally with a short RC delay, and also
feeds through the third to provide some hysteresis.
But it's more fun than that!
The circuit's performance is very sensitive to the IF bandwidth!
On this 220 machine I'm looking at, I can get .170uV 12db sinad, but
if I tune it to that, the squelch won't ever close.
If I tune to about .2uV, then I can get the squelch to close at
about .16
I have a 2M machine here to play with also, and it behaves the same
although I would have called it a "working" machine as it's squelch
actually closes somewhere nearer to optimum IF tuning.
The interesting thing is that the second transistor being class c
derives it's bias from the noise signal ampilitude. If you don't
have enough noise getting in (small cap values in the base caps?)
then you can't bias this transistor on. The third transistor pulls
base bias away if the audio squelch (NOT THE COR!) is active.
And a final thank you should go to the psychotic weasel who drew the
schematic in such a manner as to preserve neither the functionality
of the circuit, or the pinout of the chip.. I get offended by
schematics that preserve the chip pinout and sacrifice meaning, but
this one managed to sacrifice both of them in order to gain an
artful wad of electric spaghetti.
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