[TowerTalk] Force 12 C3D 10 meter problem

[Michael Lamb]

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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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