CSQ & CTCSS Support

[lilrags16]

The ability to define Carrier Squelch or CTCSS at the FM level would be a great feature that I think would help significantly for anyone who is not trying to collect digital data modes

[W3AXL]

+1 on this request. I'll take a look at the source to see if at least CSQ would be relatively trivial to add. Especially for my use case, having CSQ muting would be very beneficial.

[W3AXL]

My Sunday evening project was to try and get basic CSQ functionality working.

See PR #23 for details

[W3AXL]

Update on CSQ efforts (a year and a half later, hooray!)

I'm going to take a second stab at implementing CSQ for multifm. New approach will be to use a noise-power based algorithm that measures the level of the out-of-band (5khz+) noise and squelches on that, as opposed to a purely signal-level based squelch which is beholden to SDR gains and local RF environments.

To be determined is the most efficient algorithm for doing so. Most implementations use a high-pass filter on the demodulated FM, but I'll have to see how well this works with the reduced sample rates post-demodulation.

[W3AXL]

See PR #26 for my new attempt at adding squelch - this adds a standalone squelch utility which currently does CSQ, and in the future could do CTCSS and DCS.