Hi Tony:
This is good information - I really appreciate it. I was wondering if I
needed to add 6" stingers on the reflector. I hadn't thought about moving
the linear loading elements out farther - I probably will only get an inch
or two on those. Everything else will be pretty much as you had it.
I'll work on it.
Thanks again.
73, Jamie
WB4YDL
-----Original Message-----
From: N2TK [mailto:tony.kaz@verizon.net]
Sent: Monday, October 19, 2009 5:10 PM
To: 'James C. Hall, MD'
Subject: RE: [TowerTalk] Trimming F12 240/340N elements
Hi Jamie,
If my memory is okay I believe for the reflector I moved the linear loading
out as far as it would go plus extended the element tips to get it to 6.90.I
think the tips were 41". I believe the driven element had 17" tips. The coil
had .5" spacing between turns. This gave me 1:1 at 7.150. SWR was <1.9 at
band edges feeding it with 250' 1/2" hardline.
It was a few years ago and I no longer have the antenna. It was the MAG240N.
But it performed wonderfully across the entire band.
73,
N2TK, Tony
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of James C. Hall, MD
Sent: Monday, October 19, 2009 5:53 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Trimming F12 240/340N elements
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
WB4YDL
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