On Tue, 28 Nov 2006 22:33:43 GMT, Cecil Moore
wrote:

John Ferrell wrote:
Dabbling with EZNEC seems to suggest there may be something happening
like a 5/8 wave radiator but many factors had to be forced into place.
So that leads to my question: How do you shunt feed a 28 foot
vertical?

If you feed it at zero feet, you get a feedpoint impedance
of zero. At the frequency at which the radiator is resonant,
i.e. about 234/28 = ~8.4 MHz, the feedpoint resistance will
increase as you raise the feedpoint. Somewhere on the way up,
it will be 50 ohms with some inductive reactance so you need
a series capacitor. It's a Gamma feed. It is easy to model
with EZNEC.
I will go back to EZNEC 4 and see if I can determine what I am missing
on the Gamma match.
John Ferrell W8CCW