On Sun, 28 Oct 2007 10:30:35 -0400, John Ferrell
wrote:

I think an auto tuner with whatever whip length one can tolerate is
the best one can do with a Chrysler Minivan.

Get yourself a copy of AA6GL's "MOBILE.EXE" antenna program and try
various configurations. I'll bet you a (jelly!) donut that your
perception will change.

S.T.W.

John Ferrell wrote:
. . .
Modeling programs do not consider the radiation from the loading coils
but field measurements do.
. . .

Modeling programs do indeed include radiation from the loading coils,
provided that they're modeled as a wire helix rather than by use of the
lumped load object. EZNEC and NEC both have methods of automatically
creating a helix, making this process very easy. I believe most other
NEC based modeling programs also have this capability.

Roy Lewallen, W7EL

On Sun, 28 Oct 2007 14:52:13 -0700, Roy Lewallen
wrote:

John Ferrell wrote:
. . .
Modeling programs do not consider the radiation from the loading coils
but field measurements do.
. . .

Modeling programs do indeed include radiation from the loading coils,
provided that they're modeled as a wire helix rather than by use of the
lumped load object. EZNEC and NEC both have methods of automatically
creating a helix, making this process very easy. I believe most other
NEC based modeling programs also have this capability.

Roy Lewallen, W7EL
Ooops! I have not used that part of EZNEC yet so I accept I was wrong.
I will have to look a little deeper into why I was convinced that the
radiation from loading coils was not considered.

I still don't find a problem with publishing the article. If nothing
else it has generated discussion.

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

John Ferrell wrote:
I think an auto tuner with whatever whip length one can tolerate is
the best one can do with a Chrysler Minivan.

That will work pretty well for 20m-10m.

Modeling programs do not consider the radiation from the loading coils
but field measurements do.

EZNEC can model helical coils that does consider
radiation from the coil.
--
73, Cecil http://www.w5dxp.com

John Ferrell wrote:


Last year I purchased a radio especially to go mobile. I have yet to
find an acceptable mobile HF antenna to use on my Chrysler Minivan. I
am beginning to believe that there are no acceptable solutions to the
problem as I define it.

Then you need to change your definitions, John, -I mean that in a
friendly way. 8^)

Too often, too many time, we expect some sort of perfection. It isn't
going to happen. Mobile HF antennas are just not as efficient as a
"good" land based antenna. I'll leave the definition of good up to
everyone, suffice that the mobile antenna isn't as efficient as most.

That being said, you can have a lot of fun on HF mobile and can talk
around the world. Why let the needed compromises keep you from that?

If you are wanting to squeeze the last little bit of efficiency out of
your antenna, I would suggest a mid-loaded antenna with a capacity hat
on top somewhere (some say directly on top, but you'll have to put up
with a lot of wind loading) Use a loading coil that has as high a Q as
you can get, and bond everything you can in the van - doors, hood,
fenders, frame components, engine, radiator, exhaust system - and in
multiple places. You want as much ground plane as possible, even if at
best you don't get much.


Further, I have concluded that ALL MOBILE HF installations are poor
compared to a dipole five feet off the ground, some are just worse
than others.

I don't think that is an exact comparison, but the question is so what?
Get as good as you can afford/want to put in th elabor, and go have fun


The article simply sheds some light on the practical issues one
encounters with popular alternatives.

I think an auto tuner with whatever whip length one can tolerate is
the best one can do with a Chrysler Minivan.

Don't agree there. You could use a bug catcher or screwdriver and be
better than that.

Modeling programs do not consider the radiation from the loading coils
but field measurements do.

Tuner losses can be estimated from the software in the Arrl Antenna
Books.

If you can write a better article for QST, please do so. But please
remember, most of us don't choose the ethical we drive because of its
ability to carry a less bad radio antenna!

I'm driving a Suzuki Vitara -maybe the smallest SUV around. Yet I have
an antenna that allows me to have a lot of fun and yes it does get some
stares. If I put a football team pennant on it, everyone thinks I'm kewl.


AS for writing an article for QST, I don't think its a bad idea at all
to be critical of an article that could have been written better. That I
didn't write one does not mean that those who do have free reign to
write a poor one if they like.

- 73 de Mike KB3EIA -