Roy Lewallen, W7EL, posted:

No, that's not the problem. The problem is
that you're looking for a single voltage
between two points separated in space. There
is no single value for that voltage. If you
made some kind of "artificial ground" close
to the antenna, then there are an infinite
number of possible voltages between it and
the Earth.

As another case study, I analyzed a half-wave,
inverted-V antenna over perfect ground with the
ends of the antenna close to the ground. I
placed high-resistance (1e12-ohm) loads between
these open ends and ground as voltmeters. The
angle of the inverted-V was 90 degrees, placing
the apex of the antenna 0.35 wavelength above
ground.

The feedpoint impedance was trimmed up to be
19 + j0.4 ohms. Going right for the maximum,
1500 watts into this impedance requires an
8.9 amp current source.

The voltage to ground across the load on the
antenna endpoint is 5300 volts for 1500 watts
of radiated power.

This scales back to 1370 volts for 100 watts.

Again, this is just a special case of the general
problem. But it has a configuration that is easy to
implement in the EZNEC program and is quite
relevant to typical ham-radio, low-band dipole
installations.

If anyone wants to go over this data, or that for
the vertical, half-wave monopole, drop me an e-mail
at k7jeb (at) qsl.net and I will send over the .EZ
files.

Jim, K7JEB