With a little bit of trial and error, you can figure out which end of the radio has the AM antenna. This is the end you want to have not covered with the aluminum foil. Wrapping aluminum foil around the AM/FM radio allows me to determine within a couple of inches the source of the EMI interference.
The photo on the right is of my little AM/FM radio wrapped in aluminum foil with one corner exposed. As you can see, I was able to track down my EMI noise source right down to the very wire that was radiating the noise.
Often times when tracking down EMI issues, when you get close to the source , its so strong that you can’t pinpoint the location. Well I have a solution. The thing to do is to take some aluminum foil and wrap the AM/ FM radio in it, but leave just a corner of the radio exposed.
Shielding & Single Point Ground
Now that the source of the EMI noise has been located, and in this case, the source is the charge Controller. The first thing you need to do is to shield the charge controller. Sadly, most charge controllers have plastic cases. Fortunately for me, I already installed mine into a NEMA enclosure which provides my shielding.
Part of shielding is also grounding. In a correctly installed off grid solar PV system you should always have a ground system with a single point ground. Make sure the metal enclosure is bonded to your single point ground.
In order to further reduce EMI Noise, I added a common mode choke and a 0.1uF capacitor per the diagram below:
I will try your rfi choke for my solar charging system on my sailboat this fall.
Thanks for posting your work.