Bill Turner wrote:

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No doubt that is correct. So how about this: I have a '95 Thunderbird
which I dearly love and don't want to cut holes in. I've been think of
going to a welding shop and having a metal piece made which I could
bolt to the frame in the back and which would stick out about six
inches or so behind the rear bumper, and installing a ball mount on it.
This will keep the lower part of the antenna about a foot away from the
body and allow a nice, long whip overall. The loading coil would be in
the center, homebrew of course. :-)

And not a hole in sight.

Comments?

Bill, W6WRT

I'm not sure why, but most amateurs don't seem to realize that the whip
isn't an "antenna" and the car "ground", but each is half of a
dipole-like antenna. The car part is often much more important with
regard to radiation characteristics and efficiency than the whip part.
With the arrangement you suggest, the antenna consists of a vertical
wire -- the whip -- and a fat, horizontal "wire" -- the car. Whatever
current flows into the whip, an equal current flows over the outside of
the car, originating at the base of the whip.

Any antenna with a low horizontal wire will be quite lossy, because the
wire's current will induce a heavy current in the lossy ground beneath
the wire, or car.

The best arrangement, as others have pointed out, is to mount the
antenna right at the center of the top of the car. This makes the car
"wire" vertical, a much more efficient arrangement, which the
"shootouts" consistently show. You'll also find that larger trucks,
which effectively form a longer vertical "wire" for the car part, outdo
smaller ones for the same whip.

Of course, sometimes you don't have any choice, and you just have to do
the best you can. I once had a bumper mounted antenna consisting of a CB
whip base loaded with an inductor wound on a powdered iron core to
resonate on 40 meters. The car was a VW Squareback, so the antenna had
the increased disadvantage of proximity between the square back and the
antenna. As others have pointed out, this can reduce efficiency farther.
Yet I had a successful QSO with JA while driving down Highway 101,
running 8 watts, CW. So you can still communicate and have lots of fun
even with a very sub-optimal system. But anyone wanting to improve his
system has a much better chance of doing it if he has a basic
understanding of how the antenna really works.

Roy Lewallen, W7EL