Maybe a choke would isolate the feedline.
John KK9A
To: towertalk@contesting.com, Force12Talk@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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