[TowerTalk] Force 12 80M Sigma vertical problem

[john at kk9a.com]

Maybe a choke would isolate the feedline.

John KK9A



To: towertalk at contesting.com, Force12Talk at qth.com
Subject: [TowerTalk] Force 12 80M Sigma vertical problem
From: K7LXC
Date: Thu, 20 Nov 2008 18:23:27 EST


Howdy --

    I recently installed a Force 12 80M Sigma.  It's like an H on it's side
and fed asymmetrically which means the feed is  off-set so you can reach it
from the ground. It's a shortened antenna so  it's got big loading coils at 
the
feedpoint.

    I got the antenna to resonate at the proper  frequency (3.775 or so) 
with
decent SWR (1.3 or so to 1). But as soon as I  hook up some coax to it, the
resonance goes up 75 kHz or so and the SWR goes to  over 3:1. I tried 2 
coaxes
- 50-75 feet of RG-8X and RG-8. It seems like  the coax is transforming
something but I don't have any idea what's going on or  how to fix it. Any
ideas are
appreciated. Help!

    We're going to contact F12 but don't think they'll  be able to help 
since
the new owner is not an antenna engineer, did not design  the antenna and
probably doesn't have any hands-on experience with the  antenna.

Cheers,
Steve    K7LXC
TOWER TECH
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