On Sat, Dec 06, 2008 at 03:18:30PM -0800, Brian Sarkisian, KG8CO wrote:
> I have 125 ft of Rohn 45 with a 4 element KLM 40 meter beam on top.
>
> 1. At what height would you attach the top of the gamma match?
This might not be the answer you are hoping for - but I think your
tower is too long electrically to work well on 160. I have never
heard of someone having a tower that high that really worked well.
It is was about 70 feet tall - it would probably be great.
I think one thing you might think about is isolating part of the
tower at the bottom - say - say between 40 and 60 feet using a
trap (see ON4UN's book or I can describe it if you want).
This would put the "ground" of the gamma match up at 60 feet in the
air - and then you can use elevated radials that are 1/4 wave
long (hopefully you have room for a few of them). You can probably
avoid using a gamma and use the N4KG reverse feed method.
This would essentially give you a ground plane antenna which should
work very well.
If you do make this work with just a gamma match at the ground - and
it proves to be an effective antenna - I will eat my words!! I just
haven't seen this work for the people that I know that have tried it.
73 Tree N6TR
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