[TowerTalk] WARC7 Problem

[N2TK, Tony]

Hi Tim,
When I first assembled my WARC-7 I got the following resonances in the shack
with the antenna at 104' and using 250' of 7/8" hard line.
25.13 - 1.1:1
17.8 - 1.2:1
9.77 - 1.1:1
The coil spacing was set to 1/2" between turns

I then added 1.25" to each side to bring 12M to 24.97
Shortened 2" each side to bring 17M to 18.07
And shortened by 3.75" at each clamp (7.5" total per side) on shorting wire
on 30M to bring it up to 10.08. 
Felt that was close enough.

Let us know how you  make  out.

N2TK, Tony

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Tim Rife
Sent: Sunday, September 02, 2007 11:42 AM
To: towertalk at contesting.com
Subject: [TowerTalk] WARC7 Problem

Anyone out there have some experience with a F12 WARC 7 beam?  I need some
help with 12m.

I just installed a WARC7 beam on the 90 foot crankup yesterday.  After some
tuning, I got 30m and 17m to resonate in band at about 10.125 and 18.100 and
the swr is 1.2:1 at resonance - excellent.  However, 12m has an swr problem.
The driver tips for 12m were drilled for 28", but the manual calls for 24".
I tried them as drilled and it was resonant below the 12m band and swr up
over 2:1.  Lopped off some length so it now matches the drawing in the
manual which calls for 24" driver tips.  It is now resonant above the band,
around 25.25MHz and the swr is still up close to 2.3:1 at resonance.  So,
obviously, I need to add a little length back to drop the resonant frequency
but I doubt this solves the high swr.  I tried the hairpin spacing initially
at 1/2" per the manual and also spreading the coils to about an inch or so
spacing between coils.  I don't notice much difference in swr on any of the
bands with the changes to the hairpin.

Other antennas on the tower are a Magnum 240N about 7 feet above the WARC7.
The WARC 7 is just above the thrust bearing at the moment.  Measured values
above are with the tower extended.

Anyone have any ideas on where to go next to get the swr down on 12m?

Thanks/73

Tim
KK9T

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