An interesting day, with mixed, and rather confusing, results.
Lee, I went through your steps but I wouldn't say any one made a bigger difference than any other; apart from the power, which returned the radio to normal.
I then moved both aerials so that they are now at least three feet from my transponder aerial; they are tucked inside the seat frame, one either side, and slightly forward of my body. This may not sound ideal, but it (eventually) seems to have worked - see the attached 'Traffic' pic; 169 aircraft received whilst airborne! This is way more than I ever saw before. I say 'eventually' because I only saw this massive increase in the number of aircraft received after I also swapped out my 1090 MHz aerial for the one that came with the replacement ADS-B dongle I bought to replace my originally faulty one; I would say this new aerial received perhaps 10 times as many aircraft when sited in the same, new position. I also cut it down to size (half-length). Both my original aerial and dongle therefore appear to have been faulty.
In flight I saw way more traffic than I had ever seen before. And I also started getting very many audio and visual Mode S alerts; so many that I had to silence the audio. It was only when I landed that I realised this was most likely because I had the settings wide open; see' Config' pic attached. I had to do this with my old set-up in order to receive any traffic. I will now close the filters down a little.
And the best news of all... no radio interference; all crystal clear. Whilst I was also using my second Anker 20100 Power Core, I think it way more likely that the noise issue was resolved by moving the aerials - so Peter it looks like you were right.
So that's all the good news. The less good news is that I still can't get my own registration to appear on the traffic list. I know I am broadcasting ADS-B out; see 'FR24' pic of today's flight as attached, and note that I definitely would not have posted such a clear trace at my low altitude under Mode-S MLAT. I don't understand what's going on with this, but just to add one more weird issue into the mix, on landing I cycled through my transponder's settings and you'll see in the 'TRT800H' pic that the position field reports 'wrong data'. It has never said this before. The Funke manual says that this means no valid position is being received; it would show 'no data' if no position information was received. But the PAW GPS fix was strong, the NMEA and baud settings are correct; and the FR24 track is perfect.
Any ideas?
Stu