A few years ago, I removed the storm damaged TH6 from my 70'
tower and replaced it with an A3 that had been sitting at 40
feet, below it.
I could not get a suitable SWR (i.e., <2:1) on my 1/4-wave,
half-sloper after that. The tower termination point was about
four feet below the antenna on one of the tower legs. I changed
the bottom leg length, but it just would not work as well as it
did when the TH6 was up there.
One afternoon, while getting ready to do some other work on the
tower, I loosened the sloper at the lower leg end and climbed the
tower. I moved the feed point of the sloper right up to the
pointy section neck of the 25g top section. I checked the SWR
with my MFJ 259 and it was lower than anything I had gotten when
changing the wire length.
I finished up the work on the tower, tightened up the sloper at
the lower leg end and checked it out at the station. With one
adjustment (shortening the sloper by 18"), I achieved 1.1:1 SWR
at 3520 kHz. Good enough for me.
Hope you solve your problem.
73,
dale, kg5u
kg5u@hal-pc.org
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