Talking of radio RF interference...
Another source of radio interference is the 12-9v DC converter that runs the radio. Again a cheap Chinese job.
I tried a strip-down of the (much better) original DC converter that came with the radio, but you have to be so careful about anything touching the coil inside it, as that immediately gives radio hiss.
Going back to the cheapo unit, if I hold the outgoing wires from the DC converter, all hiss stops (repeatable 100%). But I don’t think me holding the wires is a long term solution.
I tried a ferrous ring, but no difference. So I spanned the two wires with a 1,500 ohm capacitor, and that stopped most of the hiss. Not as good as me, as a suppressor, but nearly there....
Is there anything better I can use, to stop the hiss by the electrical feed? A decent DC converter would be nice, but cannot find one in that 12-9v range.
Cheers,
R