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I asked this question recently. From the comments I learned that squelch is not a hard and fast thing, and that many considerations might go into determining a reasonable value, depending on use, the system, etc.

In my system I've decided to average power levels on the frequency of interest. I use a moving average, so that average might change dramatically over time. Somewhat arbitrarily, I decided first to use $3\textrm{ dBm}$ up squelch. So for example, if the power at the frequency is at an average of $-11\textrm{ dBm}$, I let the signal pass at $-8\textrm{ dBm}$.

I was getting way too much coming through, though (which indicates I don't understand much about the signal variance?) So I changed it to $6$-up $\textrm{dBm}$. But, still a lot of garbage goes through.

  • $3\textrm{ dBm}$ means doubling the signal, right? Is that not sufficient for something like, say, an analogue voice channel? is $6\textrm{ dBm}$ up still too little, in typical application? I really have no idea where ballpark / acceptable ranges are even. I just need a little direction.

  • I am considering combining my above technique with a static squelch level (ie. $x\textrm{ dBm}$ above average, but must be above $-x.x\textrm{ dBm}$). Is that also a typical approach?

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