trunk lip mount for HF
 

On Monday, February 7, 2011 1:45:46 PM UTC-6, Jim Lux wrote:


As far as the losses go.. just put the base of the antenna (feedpoint)
up higher (mount the antenna on a stalk, as it were). You WANT the
current in the stalk to couple to the car body. The losses in a few
feet of wire to connect the ground aren't a big deal (after all, the
antenna itself is just a piece of wire, and the losses in that are
presumably acceptable)

It will still be fairly lame compared to the whip
mounted on the body of the vehicle. It's not that
ground wires are lossy, the biggest problem is the
lack of real metal under the base of the antenna.
Heck, I once mounted one on a piece of stout angle
iron which was on top of the bed right behind the
back cab window of the truck. I had extra strap
grounding the angle iron to the bed of the truck,
and the whole truck is bonded together.
The antenna was lame. :( I could tell the difference
the first time I use it. When I moved over to the top
of the utility bed toolbox, it came back alive as normal.
He could try it, but I wouldn't be expecting too good
of results. But.. I am spoiled on using good mount
locations, so I am admittedly picky. :/


One way to think of a mobile antenna is as a dipole with a wire on one
side and a very odd shaped ball of wire on the other.

This is sort of true, but not totally.. It's still
going to act more like a vertical on a poor ground,
than a perverted dipole. One reason I know this is
because no matter what I mount my whip on, it's
resonant frequency never changes much at all.

If it acted more like a dipole, even small changes in
vehicle size and mount location would drastically
detune the antenna to the point it would have to be
retuned a bit. But I've never seen this to be the case
with mine. No matter where on the truck I mount it, or
even if I slap it on a totally different small car,
the antenna tunes the same frequency. That tells me,
it's actually much more like a vertical with varying
qualities of ground, than a dipole with changing lengths
on one side.
I know many claim this is the case, including Roy and
a few others that are quite knowledgeable, but I don't
totally buy it judging from my experiences.
Even when I mounted the antenna on the lame performing
angle iron, it tuned the same place. It just didn't
radiate worth a hoot. When I moved it to the toolbox
with decent metal under the whip, it tuned the same
place, but it radiated much better. One of my trucks
has the whip mounted on the side of the cab, not much
lower than the roof line. It's the best performer out
of all the mounts I've tried. The base is high up, and
the antenna is tall. So needless to say I'm fairly
spoiled. :/


The real thing on the whole grounding thing is to make sure that all the
pieces of the car are grounded together, and that your antenna "ground"
is connected to a big piece of metal. Bumpers, for instance, are often
electrically isolated from the rest of the car by the shock absorbing
mounts.

Nothing wrong with that advice, but I think it's most
important to have that big piece of metal under the whip.
It's not going to do much good if it's a few feet away and
connected by wires, or even thick strap. I've found this
out the hard way.. :( But again, I am picky.. And spoiled.
:/