Paul_dbnut

Oho, John, maybe Teensy added that after I looked in on it a long time back, or I just didn't understand what it was doing. Can't remember.

Re: I-Q "pseudo-stereo", that's something various people provide (under various names), but if you listen carefully it has the same "disembodied" character as wrongly-phased stereo - you can't get a solid focus on individual components. It's a waste of time, except as a special effect.

SAS or "sideband binaural" "does the business" because the 90 degree phase shift (Hilbert) in one channel as it were compensates for the 90 degree quadrature of Q. I'll call the result Q*.

Then summing I+Q* gives LSB and I-Q* gives USB, according to the standard (now almost never used) "phasing method" of sideband selection.

With this, sending phase-coherent LSB to L and USB to R we're really motoring because (under perfect propagation and DSP) the phase-locked station is 100% centred in your head. Noise (non-coherent) is spread across the sound stage (unlike with plain SAM). Adjacent channel muck is off to the side. Effective SNR is greatly enhanced, maybe by 6 dB.

Next, the Luxembourg effect spoils this, up to a point, with the wanted station wandering around a bit. But your brain still tracks it OK.

Next again, a co-channel station can often be distinguished by slight offset in position or (maybe most often) by wandering around - so the brain gets a bit of help here as well.

The Spanish or UK Single Frequency Networks (SFNs) on MW are a very interesting special case. A jumble with AM or SAM can sometimes be clarified a little with SAS.

And lastly, something you don't provide is free vernier tuning to override the PLL. A range of +/- 10 to 50 Hz would cover most MW carrier offsets and, with a resolution of about 0.1 Hz, allows you to "tune in" individual offset stations. That brings them one by one centre stage (albeit with slow wandering) and can emphasise weaker stations in the presence of significantly stronger ones.

That really does work. Using Gnu Radio Companion on IQ recordings, I've resolved both a US plus a Canadian station on one channel underneath a much stronger local station. It's painstaking work, but that's DXing for you.

I'm not saying this is necessarily the best technique for all purposes - for example the recent SDR# channel cancelling is a stunning piece of work. But it's a simple "upgrade" for any SDR software and has never been generally exploited.

One last point. For general listening SAS has no advantage over SAM, and may even be inferior. But it is a specialist tool that performs miracles (well not quite). And its value cannot be appreciated from only a casual glance - you have to listen and get used to what it's telling you. And yes, some listeners may feel uncomfortable, a bit disorientated.

Sorry if I've bored you. I'd hate for this to be a "button" that no-one understands and just gets passed over.