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[TowerTalk] Trimming F12 240/340N elements

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Subject: [TowerTalk] Trimming F12 240/340N elements
From: "James C. Hall, MD" <>
Date: Mon, 19 Oct 2009 12:41:36 -0500
List-post: <">>
Hello TT:


Does anyone here have experience with trimming the element lengths of the
driver and/or director of the F12 240/340N ? I have the 3 element version
and each element starts out the same length as the reflector with tips of
38.5". With coax and balun attached, I am to raise each element as a dipole
and trim the driver and director to the correct frequency. I first started
with the reflector to verify that the frequency of 6.90 MHz was correct.
After mounting on a push up mast and raising to a height of 20 feet or so,
my meter indicates a dip in SWR at 7.017 MHz - 117 kHz higher than expected.
It would seem that the reflector is about 6" too short on each end.


The instruction manual states that the element will shift upward in
frequency about 15 kHz between 15' and 30'. Below this height there is too
much ground coupling. I see the indicated 6.90 MHz at only 7' above ground.


Again does anyone have information on this process ?


73, Jamie


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