There are two quite separate ways which ground affects a vertical
antenna's performance.

The first is loss due to current returning to the antenna base when the
antenna is grounded, or induced in the ground under an elevated radial
system. To minimize loss, you want as much of the current to flow
through radial wires as you can. The power loss is I^2 * R. For a given
power input, I is much lower for a half wave bottom fed vertical than a
quarter wave bottom fed vertical. So the loss due to the conducted or
induced current is much less, and you can get by with a much simpler
ground system with the half wave vertical and still have low loss.

This ground loss is usually the chief determining factor of a vertical's
efficiency.

The other effect of ground is that the field from the antenna reflects
from it some distance from the antenna. The reflected field adds to the
directly radiated field to form a net field which is different at each
elevation angle. This is a major factor in determining the antenna's
elevation pattern. The conductivity and permittivity (dielectric
constant) of the ground affect the magnitude and phase of the the
reflected field, so the pattern changes with ground quality. In general,
the more conductive the ground the better the low angle radiation.
However, you can't compensate for this factor when the ground is poor by
improving the ground system. The reason is that the reflection takes
place much farther from the antenna than nearly any ground system
extends. And low angle radiation, where the improvement is most needed,
reflects the greatest distance away. The only way to improve the
situation is to move the antenna to a location where the ground is
better, which usually isn't possible or practical.

Because of the two separate effects, the overall field strength might be
better or worse as the ground conductivity improves, and it might even
be better at some elevation angles and worse at others.

Roy Lewallen, W7EL

Yuri Blanarovich wrote:
"Cecil Moore" wrote in message
...
Al Lorona wrote:
It's funny to think that really terrible ground can have an advantage
over pretty good ground.
Free space is just about the most terrible "ground"
that one can imagine. :-)
--
73, Cecil http://www.w5dxp.com

So much disinformation by W8JI School of DC circuitry :-)

Modeling various configurations shows benefits of good ground, especially
for taller than 1/4 wave radiators.
Myth that half wave radiators do not need ground is spreading like snake oil
wild fire. They need it but "looking" for it further out, not just at the
base.
I will anytime trade good ground (mirror) for lossy (RF sponge) ground. Its
just where the radiator is "looking" for the mirror, taller one - further
out, enhancing signals at lower angles.
3/8 vertical with some 3/8 physical length radials start morphing into far
field.

Yuri, K3BU.us