On Wed, Jan 31, 2007 at 07:07:58AM -0800, Paul Baldock wrote:
> At 07:28 PM 1/30/2007, Tree wrote:
> >These towers are really too tall to do any kind of shunt feeding.
>
> How tall is too tall?
>
> I'm using a 140ft tower with a full size 40M beam on the top, which
> must be electrically well over a quarter wave. I'm shunt feeding it
> at 60ft with an omega match.
I think this is probably getting close to too tall.
A tower this tall is begging for a 4 square of 1/4 wave verticals to
be hung from it.
I have never heard of a grounded tower being loaded as a vertical that
approaches 1/2 wavelength electrical height really working well (please
correct me if you feel yours is - getting ready for the flood of e-mail).
Probably a better antenna would be a 1/4 wave sloper - attached near the
electrical center of the antenna and enough of a ground at the bottom to
convince the current not to flow down.
I have a 105 foot tower with a 3 element full sized 40, and when I tried
to make it work as a vertical, it was significantly down from my shorter
tower (72 feet + 8 foot mast with 5 elements on 15 at the top of the mast
and 5 element 20 at the bottom of it).
I feel my current tower is pretty close to a 1/4 wavelength electrically
and the results speak for themselves.
Tree N6TR
tree@kkn.net
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