Early demonstration of "channel nulling"
Here is a very early demonstration of using the Kiwi's synchronous AM detector (SAM) to subtract one sideband from the other. So a strong on-channel signal that is covering up a weaker one (either on-channel or close by) can be attenuated. This is something I'm tentatively calling "channel nulling". There is much work to be done, but this is at least an existence proof.
In the first image there is a local powerhouse on 882 kHz and a much weaker carrier on 880 kHz can just be seen in the RF waterfall (green arrow).
In the second image "null LSB" has been selected from the new menu on the SAM line of the audio tab (bottom right). This puts the SAM detector in "SAL" (synchronous AM LSB) mode such that the USB component is not passed through to the audio. However, just prior to that the USB component is subtracted from the LSB, and, given the sideband symmetry of AM signals, the LSB is effectively nulled (to a varying degree). In the spectrum display above the waterfall you'll note the weak station carrier 2 kHz away now appears above the noise and, sure enough, a Spanish language station can be heard which was impossible previously.
The "spectrum display" in this case is not the usual spectrum data from the RF waterfall but rather a single-sided spectrum of the audio channel (hence symmetry either side of center). Note that an extension called "FFT" has been selected. This is going to be an expansion of the existing "integrate" extension to include more general audio FFT and spectrum capabilities.
The RF waterfall doesn't change between these two images because it is from the RF/IF path and not the demodulated/nulled audio.
This technique is not perfect. Due to the subtraction involved It depends on excellent USB/LSB signal symmetry which can be easily upset by frequency selective fading. A very common problem on shortwave and medium wave at night (at a time when you're most likely to want to use such a feature). But in the presence of fading the nulling effectiveness will vary and it just might give you the chance to "bag a new one" on MW if conditions are right.
As usual, many thanks to Youssef of AirSpy who recently pioneered this idea. A superior implementation is found in SDR# (the "Co-Channel Canceller" https://swling.com/blog/?s=co-channel). Maybe someday I'll understand how he does it (but probably not, lol).