HI FOLKS,
Well the mystery is solved.
I checked the resistance between the fender panels and the vehicle frame
and the resistance was sometimes as much as 2 ohms. Most of the time
the resistance was about 1.5 -.5 ohms. Doesn't sound like much, huh.
Well, I got out my drill, attached a wire sanding wheel, crawled under
the truck and started to locate places to attach 3/4" copper braid.
The average length of the braid is about six inches long (to reach from
the frame to the fender.
I used hanger clamps from the electrical supply store rather than drill
into the fender metal. It was much quicker to just sand off the paint,
apply anti-corrosion gel (Qualco -- found at auto supply stores to
prevent battery contact corrosion and works great for dis-similar metal
connections,etc,), install clamp, bolt braid to clamp and run braid to
bolt located on frame (I would remove the frame bolt and also sand that
area till bare metal was visible, then coat with anti-corrosion gel).
I started attaching the the ground straps at the rear of the truck.
First the fender next to the mobile
antenna, then the rear door hinge was by-pass strapped, then the rear
panel and then the other rear fender. I also did the front fender by the
battery. At that point I tried the rig on 75m. Before the grounding
straps were installed one utterance and the engine would shut down.
After the above mentioned grounding straps were installed I was able to
operate at full power with no problems.I I'd have had several QSO's this
evening on 75m with not a hint of an engine problem. I've still got
four doors and the front fender to apply ground straps to and I will do
it even though the problem has cleared.
I did also install ferrite clam shells on the control head remote
connection cable. I needed ten clamps to reduce the RF on the cable
(prior to installing the grounding straps). The ferrite does work but it
takes a lot of it and at the prices being charged for it I think the
copper strap is a least cost method to resolve the RFI problem. The .01
ceramic capacitors across the screwdriver control wire had no effect on
the vehicle RFI problem, the caps did not remove the RF from the
screwdriver control cable and five ferrite cores with one turn loops on
the cable also didn't resolve the RFI problem for the vehicle.
IT's very impressive to see how just a few ohms resistance can make such
a major change in
performance.
The RF SKIN EFFECT is alive and well...this would have been a wonderful
lab experiment for
an RF101 class. Practical experience is priceless along with some solid
understanding of the theory involved.
I'll scan in some pictures of the grounding connections if anyone is
interested in the clamp approach...
Have Fun,
dave
WA3GIN
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