We've suffered a similar condition with our 4 yo Air-X turbine. I believe that it originates in the pulsewidth modulation that they use to regulate output. At least in ours, the RFI does not start until the regulator
starts to crank back on the charge rate. At any rate, it is a pita for sure. Contacted SWWP and they suggested twisting the conductors leading into the boat from the turbine. It had taken me many hours to get those wires led through, and I wasn't about to take them back out so I could twist them, so I can't comment on that approach.
Our response is simply to switch the turbine off when on the radio
. If you try ferrites or bypass caps, I'd be interested to hear how it works. Incidentally, we've noticed that the RFI propagates for at least a hundred metres or so, 'cause we've heard it coming from other boats on many occasions.
It is a real blight on an otherwise fairly well engineered device.
73 from Jim N9GFT/VK4GFT
s/v Insatiable II lying Mooloolaba Qld Oz