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Topband: Antennas

To: <topband@contesting.com>
Subject: Topband: Antennas
From: w7iuv@earthlink.net (Larry Molitor)
Date: Tue, 28 Aug 2001 15:09:09 +0000
At 09:39 AM 8/28/01 +0200, i4jmy@iol.it wrote:
>Since we are after the very best we can do, why not sharing also what's
>good and what's not when playing with capacitive loading ?
>After all I think that careing about the best way to apply an idea,
>expecially if good, has some merit and the opposite hasn't great.

Mauri,

That's exactly why I presented the problem to the list. This is, after all, 
AMATEUR RADIO, not a military exorcise or commercial broadcast. Just a 
bunch of hobbyists trying to do the best they can. Most topband ops work 
with less than idea QTH's. Given the space and height restrictions MOST of 
us have, shouldn't we spend some time exploring ways to optimize antennas 
for this type of QTH?

It's real tempting to just hang wires off the vertical section to resonate 
it. I was looking at this very solution until I did some measurements and 
verified with computer modeling. Even than I wasn't sure, so asked for 
verification from the list.

I think we have a consensus that drooping wires from the top of a 
relatively short vertical section to a point near ground is not a good 
thing. We also have consensus that a "hat" properly implemented is the best 
solution. However this solution does not address the original problem, i.e. 
it is not physically possible to do that!

My solution to this problem has traditionally been to use inductive 
loading. Since I have the experience, ability, and most importantly, the 
machine tools needed to build structurally strong loading coils and masts, 
this has worked well for me. Others with different skill sets and resources 
may need a different solution. Personally, I would like to explore other 
options.

It would seem that a mix of "hat" and inductor may be what's called for, 
but where is the dividing line? Given that a "disposable", limited space 
antenna may not be able to have a hat any bigger than Tom's mobile antenna, 
where do we want to put the coil? Is Q really important or is it's effects 
"lost in the noise"? Questions, Questions. There is not enough time 
available for me (or maybe any one person) to do the modeling required to 
evaluate all the possibilities, but as a group we may be able to come up 
with some better guidelines.

73,

Larry - W7IUV


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