Scott wrote:
Now it's on my F-150 on a mount I made up that goes
into my receiver hitch. I ran a 1" wide ground strap from the truck
frame up to the top of the mount, where I attached the antennas ground
wire to. Now the tuning of the whip is way off from the marks and I can
only get it tuned on 75M through about 17M. Works great when tuned on
these bands, but someday I'll miss 15M-10M...

I had the same problem with a configuration like that. The ground
strap is a radiating part of the antenna and is ground at one end
and not ground at the feedpoint. On the higher frequencies, it is
an appreciable percentage of a wavelength so the antenna is too
long. In addition, the feedpoint is located away from the ground
point something like a gamma match. Here's what it looks like:

radiating
GND---gnd strap---FP---------antenna-------------

The solution is to ground the system at the FP feedpoint. For me,
that was at the top of my tail gate.
--
73, Cecil http://www.qsl.net/w5dxp


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