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From: Hank Lonberg[SMTP:Hank.Lonberg@harrisgrp.com]
Sent: Monday, August 31, 1998 10:15 AM
To: towertalk@contesting.com; Dfmich@aol.com
Subject: Re: [TowerTalk] Force 12 C3D 10 meter problem
Just thought someone might be interested in what I discovered with my C3D
antennas
yesterday. I have had problems with my C3D stack on 10 meters since I
installed them
three years ago. They were all tuning about 27.5 MHz and the factory had no
answer for
me. We surmised that maybe the problem was the way I have them mounted right
against
my 55G tower. Until lately the band has not been all that good and so I really
didn't care
much about it, but now I wanted to finally get it straightened out.
Last week I checked the SWR on my lower antenna with my new CIA-HF antenna
analyzer
and it was tuned to about 27.8 MHz. Yesterday I checked it again and it was
tuned to 28.6
MHz!!!!! I closely inspected the antenna and could not see anything that had
changed.
After scratching my head a while the only thing I could remember that had
changed was
that last week the wind was blowing and yesterday it was dead calm. I wondered
if the 10
element driven element might have been blown closer to the 20 meter driven
element and
thereby loading it down in frequency. I pulled out my comb that was the only
dielectric
"tool" available and used it to push the 10 meter element toward the 20 meter
element.
Looking at the CIA-HF display, I could see the SWR curve shift down in
frequency.
With this discovery, I went down the tower and found some 1/4 inch delrin rod
in my barn
and cut up bunch of 8 inch pieces. I went back up the tower and loosened the
"U"
clamps to allow the boom to be turned 90 degrees so that the elements were
parallel to the
tower. This allowed me to go up and down the tower and to place the delrin
sticks
across the end of the 10 meter element and the 20 meter element and fastened
them
in place with black electrical tape. Using the CIA-HF, I was able to fine-tune
the 10 meter
driven element right to 28.4 MHz.
The amazing thing to me is that this has not been brought out before, has
anyone else
stumbled across this problem?????? A 1 MHz swing from no wind to fairly heavy
winds is
amazing. I suspect that many people put up their yagis when it is calm and
then never
check out the SWR again.
Now, I don't care how hard it blows, the SWR should remain unchanged even on 10
meters.
73/Mike, N7ML
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