> You could T the ends of the T-top for extra loading.
>
> >From experiments I made at 100 MHz, a T looks like
> about 10% longer than the distance from the base of
> the T to one side of the top.
I'd suggest Teeing the top as much as possible and adding a loading coil at
the base. That should be much better than folding over the entire upper end
of the antenna!
"Linear loading" or folding the element back on itself is extremely
ineffective if done at the open end of an antenna. The loading effect is
nowhere near equal to the amount of wire in the folded section, contrary to
popular folklore.
"Linear loading" is also not so hot when implemented at other places in the
radiator either. If a lumped inductor with state-of-the-art Q is placed at
the same ***effective*** point as the linear loading, the lumped inductor
antenna will be more efficient. Some recent mods to a 75 meter beam have
shown this, as have direct measurements I've made on test verticals.
73 Tom
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|