Supposed comparison of Mobile HF Antennas in November QST
 

charlie wrote:
Roy Lewallen wrote:
QST editors can't be expected to be experts on all the topics they have
to deal with. Over the years, they've dealt with the problem in various
ways. One was to establish a pool of "Technical Advisors" -- volunteers
SNIP
Didn't look to see what you are using to post but could you please
set your line length correctly. Sixty eight characters would do
fine! (E.G. as Thunderbird has corrected your post above.)

I'm using Thunderbird 2.0.0.6, which defaults to flowed rather than
fixed width format. Please see
http://kb.mozillazine.org/Fixed_width_messages. When flowed text
messages are viewed with Thunderbird (at least with mine), they wrap to
the window width. If the flowed format is causing a problem for other
readers, please email me. If it is a general problem I can force it to
post in fixed line width. But let's take the discussion off line.

Roy Lewallen, W7EL

Supposed comparison of Mobile HF Antennas in November QST
 

On Oct 26, 1:20 pm, Michael Coslo wrote:


I've considered putting a tuner on my Bugcatcher for 80 meters, but
haven't. The thing is so narrow there that the alternative is two taps
for the phone portion of the band.

That would more more for impedance matching rather than the
loading coil itself. I have no real problem with that. I've often used
simple L network tuners for matching mobile antennas.
The system I have a problem with is using the tuner as the
loading coil itself. It's usually a disaster as far as efficiency.
Maximum current is at the coil, and often that coil will be
surrounded by body metal. Not good.. Poor current distribution
through the whip, and low overall efficiency. Not good..
If they left out bugcatchers in the test, no wonder all those
tuner fed things looked so good... :(
If your antenna acts very "high Q", that's actually good. :)
It means it's probably a pretty decent radiator.
I'd be more worried if it acted overly broadbanded, or low Q.
You won't lose much if you use a tuner for Z matching in your
case.
MK

Supposed comparison of Mobile HF Antennas in November QST
 

On Oct 26, 5:53 pm, Art Clemons wrote:
Richard Harrison wrote:
No problem with a tuner. "The input power was the same on each antenna."

How can the input power be the same if it's going through the tuner? The
input power is the same at the input of the tuner, but we have absolutely
no idea what the output power from the tuner is. Isn't that a problem for
a fair test? Would not a more reasonable approach be to use something like
Wattmeter and get the antenna resonant? I've seen folks who used antenna
tuners find out the tuner can get really hot into some loads? If the tuner
is consuming some of the RF as heat, that's power not reaching the antenna
ergo not a fair test.

I may be missing the story...Is he feeding all these whips with the
tuner
alone, with no loading coil, or he feeding coil loaded antennas with
a
tuner for impedance matching?
I got the impression he was using the tuner alone, with no other
loading
coils on the whips.
I have no real problem with using a tuner for impedance matching
as long as it's not the actual loading coil.
I guess without seeing the article, it's hard to tell what his point
is.
MK

Supposed comparison of Mobile HF Antennas in November QST
 

Art Clemons wrote:
"Would not a more reasonable approach be to use something like a
Wattmeter and get the antenna resonant?"

You have a point. The wattmeter was on the input to the tuner and we
don`t know what the tuner`s loss is. If the loss is negligible,
everything should be OK, and "the input power was the same on each
antenna."

Best regards, Richard Harrison, KB5WZI

Supposed comparison of Mobile HF Antennas in November QST
 

On Oct 27, 12:15 am, (Richard Harrison)
wrote:
Art Clemons wrote:

"Would not a more reasonable approach be to use something like a
Wattmeter and get the antenna resonant?"

You have a point. The wattmeter was on the input to the tuner and we
don`t know what the tuner`s loss is. If the loss is negligible,
everything should be OK, and "the input power was the same on each
antenna."

Best regards, Richard Harrison, KB5WZI

I received back a fairly detailed email from the QST editor
involved... I will reply to him next week... I will incorporate some
of the comments on here - with attribution to the author(s)..
Everything (except private comments) will be shared here...
Right now, back to the inhumane QRN on 80 meter cqww...

denny / k8do

Supposed comparison of Mobile HF Antennas in November QST
 

On Thu, 25 Oct 2007 23:02:12 -0400, Art Clemons
wrote:

I almost could not believe that an article that starts out with using an
antenna tuner to deliver all possible power to mobile HF antennas got
published.

I also noted that the testing antenna was 360 feet away.

I'm waiting to read on here that I've mis-understood a great method of
measuring HF mobile antennas, but absent a troll or two, I don't expect
too.

As a Student of the Art of Amateur Radio with a special fondness for
antennas I found the article useful and interesting. At least as far
as it went!

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.

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.

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.

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!

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

Supposed comparison of Mobile HF Antennas in November QST
 

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.

Supposed comparison of Mobile HF Antennas in November QST
 

Art Clemons wrote:
SNIP


Roy seems to be using T'Bird which if I remember correctly defaults to 72
characters per line. Roy's post showed up fine in Knode here too.

Yes, I noticed later that he was using TB in which my default is 68
but 72 would do :) Maybe Knode automatically wraps the lines?



Charlie.

--
M0WYM
www.radiowymsey.org

Supposed comparison of Mobile HF Antennas in November QST
 

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

Supposed comparison of Mobile HF Antennas in November QST
 

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