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Message: 2
Date: Mon, 17 Apr 2006 10:23:17 -0700
From: "Al Williams" <alwilliams@olywa.net>
Subject: [TowerTalk] Vertical Moxon antenna for 40m field day
To: <towertalk@contesting.com>
Cc: Rich Patrick <rfpatrick@yahoo.com>
Message-ID: <001201c66243$a236a960$25daadd8@PAPASDELL>
Content-Type: text/plain; charset="iso-8859-1"
We are considering a 40m vertical moxon to augment our 3 element 40m wire
beam for this year's field day. Here in the Pacific Northwest the beam at
65' elevation gives good gain and wide enough horizontal beamwidth to cover
the easterly stations. However the low angle radiation is not so good.
EZNEC shows the 40m vertical moxon to have pretty good gain (~9 dbi) down to
about 2 degrees above horizon.
However I am concerned about the Brewster angle effect and that EZNEC may be
ignoring it. In looking over a number of books and articles the discussion
of the Brewster angle appears to be concerned with verticals working against
ground. I am trying to determine if the Brewster angle effect for the Moxon
negates the low angle radiation of the moxon. The 3 element beam is pretty
good down to about 20 degrees or so.
>From these discussions and the web, it appears that the low angle radiation
advantage shown by EZNEC is not going to be produced because of the brewster
angle effect.
Has anyone tried the vertical moxon on 40m that can compare it to horizontal
antenna at half wave height?
k7puc
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Al,
If you are talking about using the vertical Moxon for FD, I would
recommend against it. With your yagi at 65 feet, I think you need more
energy at higher angles, not lower angles. From New England, we put our
club in the top ten overall scorers a number of time with a two element
Moxon yagis at 40 - 45 feet on 40m. Besides not having taller trees, that
height also works out for everything we needed to work, all across the
country. It was a 5A effort, but the huge jump in 40m points was what did
it for us, with California well represented.
On the other hand, if it is DX you are looking for, then I say your
observations are along the same as mine from modeling and from experience.
At 40m, you just starting to get high enough in frequency where you can get
a horizontal antenna high enough to create as much energy at lower angles as
you can with a vertical. So it might not be worth the effort.
Dudley - WA1X
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