Topband: EZNEC Shunt Feed Model Gain

[Dan Zimmerman N3OX]

>
> 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.


There are other issues important to shunt fed towers.

NEC-2 has issues with sources in small loops.  For standard NEC-2 (not
double precision NEC-2D or NEC-4 according to the manual) that seems to be
0.05 wavelength in circumference for small square loops. Close spaced wires
need to have segments that line up with each other for best results.   And
if you connect different diameter wires in critical applications you have to
be careful.  I think you're probably combining all three of those issues to
a certain extent.

I wouldn't rely too much on the gain numbers for a shunt fed vertical
without a lot of testing in juggling the details of the gamma segmentation
to see if things converge, removing all the loss sources (perfect earth,
zero wire loss) to do "average gain tests," and other sort of advanced (and
somewhat tedious) modeling chores.

I think you can do it but I think you have to work to get correct results
you can trust, since you're probably running up against more than one
"tricky" issue...


73
Dan