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[email protected] · April 3rd 14, 06:31 PM posted to rec.radio.amateur.antenna

wrote:
Wimpie wrote:

snip

A quarter wave monopole with near vertical radials has same current
distribution as a vertical half wave dipole (use sum of current in all
radials). Of course provided that you don't have significant common
mode current in the mast or coaxial cable, as this may increase or
decrease the free space gain.

In the simulation there is no mast or cable.

This got me to wondering...

I took the model from the longer comparison post, i.e. radials at 45 deg
and 5% longer than the driven element, and looked at the currents.

The sum of the currents in the 4 radials is exactly equal to the current
in the driven element.

Then I added a 10 foot conductive mast.

This had a very small effect on the resonant frequency, SWR, and pattern,
but now there was a significant difference between the current into the
driven element and the radial/mast structure.

This says to me that you DO want to provide current choking at the feedpoint
for a GP as even if the mast is non-conductive, the outer coax shield is
conductive.

--
Jim Pennino