by kludge » Mon Jan 25, 2016 6:16 pm
Where is the antenna?
The radio (I'm assuming it's a fairly standard car/marine radio) should be in a steel box. If so it should provide fairly good shielding. Also the antenna cable should also be a shielded cable. Try moving the antenna to a different location - as far as possible from the converter.
The other thing to remember is the inverse square law. Radio signals (it sounds like the converter is generating some) are attenuated according to the "inverse square law". Meaning every time you double the distance the amplitude of the signal is 1/4 what it was.
i.e. distance is your friend.
Does the converter have an FCC mark? Many types of household electronics have to pass FCC testing, but since the product is not really intended for household use they may be able to bypass the testing. If it's a "smart" converter or an "off-line" (transformerless) converter with MOSFET switches to control the charging voltage and current it would have to pass FCC for household use.
If the radio is already in a steel box, the next step may be to put a steel box around the converter. Or at least on the under side. Or move the converter.
Another possibility - since I don't know how your electrical is wired - is to give your radio a "clean" power and ground - i.e. run the radio off dedicated power and ground wires all the way back to the battery/fuse panel with nothing else on the circuit. You could have a situation similar to "alternator whine" if there is noise on these cables. The battery makes for a really good filter.
But beware, those dedicated cables can also pick up noise from the converter cables if they are run together. A lot of people like to bundle wires together because it's neat and pretty, but this can cause big problems for audio systems.