Danny K6MHE wrote:
"Boy Richard you sure missed on that one!"

A broadcast tower over a perfect ground system is the source of radiated
energy even though its image in the ground system produces a pattern
which behaves as if there were a dipole, the lower half of which is
buried.

The earth is not radiating. It is conducting. The tower above the earth
is the source of radiation.

Every ground radial in the broadcast system (usually all 120 of them),
has a twin running in the opposite direction. All radials are tied
together at the base of the tower. So the current in the radials all
starts out in the same phase and stays roughly in the same phase as it
progresses outward. It declines in magnitude away from the feedpoint.
That`s the reason ground radials don`t need to be unlimited in length.
You don`t need radials after the current plays out. As current travels
in opposite directions in the groind radials. the fields they prodoce
add to zero.

The two halves of a dipole are fed with opposite polarities at their
feedpoint. this puts the two halves running in opposite directions
in-phase. Their fields thus reinforce.

A 1/4-wave ground plane in free space has the same power gain as a
center-fed 1/2-wave dipole.

The matched power radiated by either ground plane or dipole is the same,
but the resistance at the feedpoint of the ground plane is only 50% that
of the dipole. Radiation resistance is defined as the resistance at the
high current point of the antenna unless otherwise specified. Radiated
power is (I) squared times the radiation resistance.

Danny did not specify where he thought I erred in my previous posting. I
said that a whip mounted on a vehicle is not exactly like a dipole. I
meant that the whip did most of the radiating because it carried a
concentration of current in the same direction while in the car body the
current is dispersed in various directions, some of which canncel in
their effects.

I still insist that is the case.

Best regards, Richard Harrison, KB5WZI