Do the blind test, and one might be surprized.
The difference between theorie and practice!
De : firstname.lastname@example.org
[mailto:email@example.com] De la part de Kimo Chun
Envoyé : mercredi 20 juin 2007 10:49
À : firstname.lastname@example.org
Objet : Re: [TowerTalk] Trapped Tribanders Turned Vertical
Funny you should mention this. Our club, Koolau Amateur Radio Club, KH6J, is
about to construct our Field Day site this Friday with another local club,
Emergency Amateur Radio Club. Featured among our antennas are two Mosley
CL-33 yagis turned vertically, mounted on bamboo with the lower element tips
only a few feet off the ground. We have been doing this with great success
for a number of years now.
There are a few critical items, however.
First, the only reason we do it is because we can place them just off the
sand by the salt water pointing to the U.S. mainland. The computer model
suggests our takeoff angle approaches 6 degrees (if memory serves). Since we
don't have to rotate the antennas during FD because of our location in KH6,
we can fix them this way.
Second, we do have problems with the traps filling with rain water as we do
have rain squalls that pass through periodically. In some years we do have
to lower the antenna and empty out the traps. We have tried leaving the
lower oriented trap end-caps loose but I don't recall how well that worked.
It is no big deal. The rising SWR tells us when it is time to do it.
Third, you must place it on a non-conductive mast so it does not interact
with the yagi elements. We just harvested some thirty foot bamboo that is
about 5 inches diameter at the bottom and at least 2-1/2 inches around 25 to
27 feet off the ground to allow easy clamping of the yagi at that height.
So, if he can meet all the criteria he can go ahead. Otherwise, I think he
should mount it horizontally like they were likely intended and try to get
it a half wavelength or more, at the lowest frequency band, above ground.
SteppIR yagis were similarly vertically mounted on Kure Atoll for the K7C
DXpedition for the same reason. With the better takeoff angle it's like
running a linear while using 100 Watts. Listen for KH6J on 20M (or 15 if it
is open) this Saturday and see if we are loud. I hope so.
Kimo Chun, KH7U
Date: Tue, 19 Jun 2007 19:00:30 -0500
From: "Robert Pack, NX5M" <email@example.com>
Subject: [TowerTalk] Trapped Tribanders Turned Vertical
Content-Type: text/plain; charset="iso-8859-1"
Without going into great detail with the reason this question is being
asked......local guy wants to put a tribander up (an A3 I think) and wants
to mount it vertically. He asked me what I thought about it. My first
thought was water getting into the traps and not draining out, or draining
out too slow.
I have never seen a vertically mounted tribander (other than triband or
better verticals). I will admit that I have never looked closely at a
trapped vertical so I do not know if there is anything different in the
sealing of the traps or not. Is there?
Could this fellow actually put his three element tribander vertical? Should
he seal the top ends of the traps and maybe put small pin holes on the
bottom ends so water can drip out? Any electrical or structural issues that
come to mind?
I will print and pass along all replies.
Date: Tue, 19 Jun 2007 20:41:37 -0400
From: "Mark Robinson" <firstname.lastname@example.org>
Subject: Re: [TowerTalk] Trapped Tribanders Turned Vertical
To: "Robert Pack, NX5M" <email@example.com>, <firstname.lastname@example.org>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
What does he hope to gain by mounting the tribander vertically?
Mark N1UK G3ZZM
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