On Tuesday, January 27, 2015 at 6:46:43 PM UTC-6, Ralph Mowery wrote:
wrote in message
...
There was no difference where the whip was resonant, same as I see no
difference between any of the vehicles I've used it on, both small cars,
and large trucks. Which tells me the vehicles act much more like an
untuned
ground radial system, than the mirror image of a loaded dipole.
A cement balcony floor with mesh "should" act about the same way.
It should be about like a mobile parked on top of a multi story parking
garage.

The vehicle acts more like a capacitor to couple to the ground instead of a
radial system.

Yep. The reason I mention this is some claim the the typical
mobile system acts more like a dipole, with the whip as one
half of an element, and the car body the other. But in actual
operation, I've never noticed this to be the case.
It acts the same as the typical ground mounted vertical.

If it did act like a perverted dipole, switching to a different
size car, or even on different parts of the same car would cause
a drastic change in the resonant freq. But that has never been
the case with the various mobile systems I've run.
I've run several different mobiles with the same whip, from a small
Honda Accord, to large Ford trucks, and I've never had to adjust the
loading coil setting for any of them. The only difference is varying
levels of efficiency per the size of the vehicle, and the location
of the whip on the vehicle. The best performer is the Ford truck I
have that has a ball mount on the upper roof pillar of the cab.
It's a bit better than the other truck with the utility box mount.
All the cars had trunk mounts, and they were pretty good overall.
A good bit of metal under the whip. I used drilled hole mounts on
those. I've never used any kind of magnet mount. Both trunk mounts had
to be reinforced under the trunk lid with steel plates to take the
abuse of the fairly tall HF whips, even though I was using fairly light
"plastic bugcatchers". Still lots of rocking motion that will distort
the metal of the trunk lid pretty fast if you don't.