This was done by Don Johnson W6AAQ & described in his book 40 years of HF
Mobileering. He mounted another whip at the front of the vehicle & grounded
it to the frame & tuned it to resonance.
wrote in message
ups.com...
On Nov 3, 8:22 pm, "Yuri Blanarovich" wrote:
Exactly!
Vertical mounted on a conductive vehicle body behaves as a vertical
monopole - radiator working against the ground plane - car body. It is
apparent that the idea that car is the "other half" of "asymmetrical
dipole"
is misleading and not applicable to the case. Mobile antenna behaves like
any other vertical monopole over conductive ground plane, radial field,
radials - regardless of their size and definitely not as the other half
of
"asymmetrical dipole" and practically not affecting tuning, which is the
case with any real di-pole.

73 Yuri, K3BU

Just pondering.. Another thing that bothers me about the mobile dipole
theory is that the body element is not resonant in most cases, and
thus
should not act as a decent working dipole leg in those cases.
Now if you by chance had a vehicle with the whip mounted at the rear,
and the front vehicle length by luck happened to be resonant, then
yes,
I could see much more of a dipole effect.
But say with the typical low band HF mobile, the car is not even close
to be capable of being a resonant element.
So I'm also tending to believe it acts more like a typical short
vertical
that is mounted on a varied size sheet of metal, but also coupling
with
the earth.
The coupling to earth can be verified by driving over certain types
of
ground, highways with rebar, etc.. Some areas are noticeably better
than others.
MK