I have installed a Cushcraft A3 at 30 feet maximum on DX-Peditions using
factory settings and the antenna worked fine in the segment that I set it
for. I think something is either wrong with your measurements or the traps.
If you have deviate much from the factory settings so it will be resonate
inside the band, the director and reflector dimensions may also be off and
you won't have the proper pattern. Before condemning the antenna, I would
use another method of checking the SWR.
To: towertalk@contesting.com
Subject: Re: [TowerTalk] tuning A3s
From: jim Jarvis <jimjarvis@optonline.net>
Date: Thu, 19 Mar 2009 15:21:20 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I threw a connector on the end and used the AEA analyzer with the tower
standing up..not cranked up but at 21 ft..and it's still the
same..low on
all bands... On 20 lowest at 13900(1.63) , on 15M lowest at 20900
(1.1), and
on 10M lowest at 27600(1.08)...I assume just shorten the dipole a bit?
Tom N3ZC
Tom,
It is normal for an antenna to appear resonant low, when it's close
to the earth,
and to have its vswr center rise, as the antenna goes up. Each
antenna and site
are a bit different, in that regard. But in general, I would expect
to see the vswr centers
move up by 100-200 KHz, in going from 20-60'.
Two approaches:
1) Crank up the tower to full height and repeat the measurement.
Bring it down and make necessary adjustments.
2) Shorten the DE a bit, then put the tower to full height, repeat
measurements,
and bring it down to fine-tune.
My guess is that your vswr center @ 55' will turn out to be
14,050-14,100, with no adjustment.
If you're looking for higher in the band, then perhaps try shortening
a bit, first.
Since they're all low by about the same amount, if you adjust the
center, you'll bring them all
in. Once you get 20 where you want it, you MAY have to diddle with
15 and 10 a bit, although
usually, the factory settings work fine.
Jim/N2EA
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