"Roy Lewallen" wrote in message
...
I should elaborate a little.

The average gain is the ratio of the total power in all directions at a
great distance (beyond the point where the surface wave has decayed to a
negligible value) to the power into the antenna from all the sources.
(There's a factor of two also involved when using a ground plane with NEC
but not with EZNEC.) So the average gain is the efficiency if you consider
ground reflection and the decay of the surface wave to be part of the
loss.

Roy Lewallen, W7EL

I was using average gain for my calculation of efficiency; i.e.
XNDA = 1001, or 1002. I have also been considering
the factor of "2" in the results. To be accurate, and to
determine the radiation resistance of a structure, you do
need to include the surface wave. The only way I
can think of doing this is to sum "E X H" close enough
to the radiating structure so as to include all its
elements. At the moment I am using Excel
to compute the Poynting vector.
Even then, there is some question as
to how much ground absorption effects the results
between antenna and the hemispherical radius
of computation. I have noticed some weird results
if you get too close to the ends of a buried radial system.

Regards,

Frank (VE6CB)