Squelch improvements

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Posts: 27
Joined: Thu Aug 27, 2020 5:41 am
Location: Olsztyn, Poland

Squelch improvements


Unread post by goscickiw »

Here is a list of some things that I think might improve the squelch functionality and would be nice to see implemented eventually:
  • Attack/decay settings for FM and AM squelch (I have an issue where the squelch sometimes randomly opens for a split second when there isn't even a trace of signal present, which is a bit annoying, and it happens even if I have squelch level set a few % above the "Auto" setting and have noise blanker enabled. Maybe this could be fixed by adjusting the attack setting / how fast it opens after it detects a signal. I wouldn't mind if it opened a bit too late, and if I was doing something where that would be a problem I could change the setting back. For AM squelch it would be nice to be able to change the decay setting, as it stays open a bit too long after the signal is gone);
  • Higher maximum setting for FM squelch (currently it has to be near maximum when the noise level is at just -80 dBm);
  • Global "Auto" button for setting the squelch value on all the currently working receivers that have squelch enabled;
  • An ASQ feature that automatically adjusts the squelch level as the noise floor changes over time (maybe by just periodically doing what the "Auto" button does, but only if SNR is below a certain level so it doesn't do this when a signal is present);
  • Use the same units for squelch level setting as the spectrum display scale;
  • Display something (for example a horizontal line) representing the squelch level on the spectrum when the mouse cursor is on the squelch level slider.
Would this be possible to implement? Could something be done differently/better? Maybe some of these are already implemented but I just haven't found them yet?

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Re: Squelch improvements


Unread post by jdow »

AM squelch can't be helped much without adding (significant) latency. For SWL this is no problem. For hams the latency ranges from annoying to deadly. SDRC, with its transmit capability, is somewhat biased towards ham usage.

FM squelch, which I've not played with for awhile, historically has been a signal level squelch. I tried to sell Simon on noise squelch, which is insanely good (except when it isn't.*) I don't think Simon made the change. If he did, I missed it likely due to a medical problem here. (Recommendation: Do not allow yourself to get old.) My test implementation had a low pass filter for audio and a more or less matching high pass filter for a noise detector. It could be set hair trigger without falsing.

* Noise squelch is deadly when a specific kind of jamming is involved. With proper noise modulation on an FM jammer you can cause noise squelch to false alarm leading to the op cranking down on the squelch setting leading to a DOS attack on the radio. In the '67 war the Egyptians met some success with this until the Israelis discovered it was happening and made some changes to their radio operation doctrine. The USAECOM rep for our group told me about it and how they were hoping the frequency hopper we were working on would obviate that problem. It did. It was a fast hopper and REALLY worked. It was too expensive. So SINCGARS radios are slow hopping, which I can very easily jam with a few parts and some software or a few other parts including a SAW delayline.


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Joined: Sat Jan 21, 2023 11:22 am
Location: Queensland Australia

Re: Squelch improvements


Unread post by lappydesktop »

I would like to see a squelch hysteresis implemented if possible , that snap off/on can get a bit tedious sometimes , with a maybe adjustable setting for the delay back on of the hysteresis like a slider , AM and SSB and FM , it'd be Nice! , cheers

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