Aloha,
I believe I have successfully transformed my elevated "ground
plane", two elevated radial 10 meter Gladiator into a half wave
vertical, center fed.
I am sitting out here near mid-Pacific listening to QSO's from JA
land all across the US mainland, even to Maine; and now,
mainland to DU land on 28480, where DU4DX, Jun, is holding
forth with QSO's to many of the states.
The center feed point is 0.7 wave above the soil below, and
around the house. All I did was to take the two "resonant"
elevated radials, and twist them together!. Then, instead
of having them go out an an angle below the feedpoint
as is done with elevated radials in ground plane
configuration, I dropped the twisted pair almost
straight down below the vertical 10 meter element.
Of course the upper half is aluminum tubing, while
the lower dipole half is a twisted pair of #14 wire.
At the feed point is still the Gladiator "unun" which
acts as a choke of coax shield current.
Measured result with the MFJ 259B follows:
28001, R=36, X=28, swr=2.0
28484, R=99, X=0, swr=1.9
and X remains at 0 ohms from 28484 up
to 28647, where R has increased a bit
to 102 ohms, and swr=2.0
R then drops steadily on up to 29.7, where:
29.7, R=15, X=11, swr=3.5
The above are the impedance's as read at the end of
the transmission line down here in the shack.
So the real part of the feed impedance has gone way up
from a measurement in the "ground plane" configuration,
where, as an example, at 28580, R equaled 33 ohms,
with X=26, and swr=2.1. Now, configured as a center
fed, half wave dipole, R is about 100 ohms, X=0, and
swr is still about 2:1.
So I wonder if I have improved my antenna efficiency by
this reworking of the two elevated radials into the
lower half of a vertical dipole??
73, Jim, KH7M
On the Garden Island of Kauai
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