You would have to model the skirt wires as a transmission line working
against the tower. There is a free program called "atlc" that can
determine the characteristic impedance. However, it only runs on
Linux. You can also try the free program Maxwell SV from Ansoft
to determine the characteristic impedance.
In your case, since your tower is close to a quarter wave, the
transmission line is a shorted quarter wave, which will look like
a very high impedance from the feedpoint, and it doesn't much matter
what the characteristic impedance is. Thus it should load up pretty
much like a cage vertical, with the tower "disappearing", assuming
you drive all three wires. You can model a cage vertical on EZNEC, etc.
I would not recommend driving only one wire and grounding the others.
Rick N6RK
John King wrote:
> Does anyone know of or have access to a modeling program for a Folded Unipole
> Antenna for 160 and/or 80 meters?
>
> I have a GROUNDED 130 foot Rohn 25 tower with nothing on top of it. The guys
> are broken up with insulators.
>
> I am thinking of not putting anything on top of it and using it as a folded
> unipole or maybe a shunt fed antenna. I think the folded unipole with three
> wires, one on each face, approximately 3 feet from the tower would be easier
> to feed.
>
> I have the tower and instead of taking it down, why not use it. I am
> considering putting my 2 element Quad on a 51 foot motorized, crank up, tilt
> over tower. With hurricane winds each summer, here in Louisiana, I am
> convinced to keep the HF antennas closer to the ground. Recently losing two
> five element monoband beams that were over 100 feet up made it clear to me
> that lower was best for HF antennas. Thanks and 73, John, K5PGW
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|