danny wrote in :

Owen,

Based upon your findings above, have you thought of increasing the
height of your model to determine at what height would be necessary to
equal the same efficiency as your 120 radial reference?

I don't think it is a simple as that Danny. With sufficient height, the
pattern changes significantly and so you cannot compare the antennas on
efficiency alone.

It might seem intuitive that a ground plane a very long distance (say km)
above earth would approach 100% efficiency, and we tend to assume that for
VHF ground planes many wavelengths above ground, the model does not
indicate that. At sufficient horizontal distance above flat earth, some
rays must reflect off the ground and so warm to soil to some extent, no
matter how high the antenna.

The study was more to answer the question whether elevated radials were
effective, and how high they needed to achieve similar performance. The
model suggests that just three radials at 2m height is about 1dB down on
120 buried radials, or about 90% of the efficiency or EIRP (since patterns
are almost identical).

Owen