Roy Lewallen wrote:
Jerry wrote:

Roy is certainly right! The vehicle is the other half of the
"dipole". It is why if you stick a bugcatcher at random on a
broomstick, it won't work: SWR will be thru the roof.. Or you could
hang a dipole for a given band (your choice), then snip off the side
that went to the coax shield (or vice versa). So, yes, the vehicle is
the other half of the antenna. You could even look at it as an
right-side up "L"!

You have to look at where the currents go. If you had a completely
symmetrical vehicle and put the antenna at the very center of the top,
the horizontal currents along the top would produce fields that almost
completely cancel, just like a bunch of radials. But when they reach the
edge and flow downward, the fields are all in the same direction and
add. So it radiates just like a very fat wire.

But if you put an antenna on the edge of the roof, then the fields from
the horizontal currents won't cancel and you'll have some radiation from
the top as well as the sides. And so forth.

Roy Lewallen, W7EL

I think I know the answer but I need to be sure. The information you
have provided suggest that I should move the antenna from the clip on
mount at the back left corner of the van to through hole mount in the
middle cross bar of my ladder rack in order to get a more omni
directional pattern out of it right? Since the antenna is a fold over
type that I can fold to go under obstructions I think I'll still be all
right if I move it there. I have a traffic directing arrow on the back
cross bar and a full sized strobe beacon on the front cross bar. Are
there any other mobile operation pit falls that anyone would care to
point out?
--
Tom Horne, W3TDH