[RFI] 40m Mobile sub-woofer RFI

David Jordan wa3gin@erols.com
Mon, 01 Apr 2002 10:09:10 -0500

Hi Folks,

Here is an interesting one...

Operating 40m mobile with FT900, Skywalker 500 (powered by stand-alone
battery not connected to engine batter or charger, etc. )and BB3
screwdriver antenna mounted (ground strap from base of ant. to frame
rails) on the rear driver side of Sport Trac.  When operating with the
driving lights off I get considerable RFI to the sub-woofer in the
truck's stereo system.  If I turn on the headlights and running lights
the RFI decreases to almost undetectible levels?

I'm guesing the rear tail lamp wires are picking up the RF from the
antenna and feeding it back to the other accessories in the truck.  By
turning on the driving lights I've perhaps changed the impedance of the
wires with respect to resonance of the antenna or by closing the circuit
have taken some of the RF to ground??? Just wondering if others have had
this experience.

My plan is to take the rear lamp wire harness and place a few ferrite
cores on the cables.  Might also try to run some braid up from the frame
to the negative side of the lamp wires.