I would need a copy of your EZNEC model to be sure, but one of the
elephant-in-the-room issues in modeling vertical antennas has to do with
modeling the ground connection.
If you look at the current in your models, you will note that the shunt-fed
version carries FAR more current than the simple model at the base of the
tower. The high current of the shunt must pass through ground or close to
ground to complete the circuit.
If you want to drop me an email with your .ez file attached, I'll take a
look at it. There are quite a few ways to depict the shunt and the
feedpoint, and you will be using but one of them. Further comment requires
knowledge of your method.
73, Guy K2AV
On Tue, Aug 18, 2009 at 10:42 AM, <k8gg@voyager.net> wrote:
>
> ...
> When I model it as a shunt
> fed tower, base grounded, with 50 feet of 1.6 inch OD pipe about 27 inches
> from the center of the tower as the shunt feed rod, the gain drops to
> about 0 (zero) dbi. The radiation pattern, etc. stays the same.
> Is this a fault of EZNEC4, or does the shunt feed truely reduce the gain
> of the antenna?
>
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