[TowerTalk] Topband: Shunt Fed Question

[Peter Voelpel]

-----Original Message-----
From: topband-bounces at contesting.com [mailto:topband-bounces at contesting.com]
On Behalf Of Tree
Sent: Sonntag, 7. Dezember 2008 20:57
To: Brian Sarkisian, KG8CO
Cc: topband at contesting.com
Subject: Re: Topband: Shunt Fed Question

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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My tower is 145 ft tall and loaded with 5 yagis starting at 63 ft from the
ground.
I feed it against two extended elevated radials at 45 ft, coax inner to the
radials via a shortening variable cap, shield to the tower.
That is the best vertical on 160m I ever used, far better then the 70 ft
tall T vertical I used for a couple of years.

73
Peter