I was getting some RFI on the sub-woofer of the Ford Sport Trac stereo
from my 40m HF antenna mounted at the left rear of the truck bumper.
The RFI would deminish when I stepped on the brakes so I presumed I was
getting RF pick-up on the wires feeding the rear brake lights.
The bed of the Sport Trac is made from composite so there is no sheet
metal to interfer with the antenna but also no sheet metal to shield the
wiring of the brake lights.
I decided to place a few ferrite clam shells on the wires feeding the
rear brake lights. Well, the RFI to the sub-woofer dis-appeared. The
wires must have been picking up the HF signal and super-imposing it on
the other wires in the wiring harness feeding the rear of the truck.
The other wires included the dc power for the fuel tank pump and the
To my surprise the noise from the fuel pump on the FT-900 transceiver
has also dis-appeared. Apparently, the fuel pump RFI was being
super-imposed on the wires in the harness and re-radiating along the
wires all the way back to the location of the antenna, where it was
picked up by the 40m HF antenna and fed to the FT-900.
Who would have thunk it,