On Wed, 13 Feb 2008 20:58:31 -0800 (PST), N0GW
wrote:

It was then that I noticed that when I
overlayed the pattern from a vertical half wavelength dipole with that
of a horizontal half wave dipole at the same center height over real
ground that the pattern from the vertical was completely enclosed by
the horizontal dipole pattern, at least broadside to the horizontal
dipole that is. The vertical dipole pattern definitely showed a lower
angle of peak radiation but no greater gain a low angles than the
horizontal dipole.

Hi Gary,

You have so much left unsaid, that it is shooting in the dark.
However, proceeding with that risk in mind....

A vertical dipole described above is not the vertical antenna that you
describe following:
The interesting question then: Is the improved performance of
vertical antennas over horizontal dipoles on 75 meters at DX distances
due to a combination of direct radiation plus radiation from the
ground in the area of strong ground wave strength out hundreds of
meters? Is the ground wave leakage providing additional low signal
strength in both transmit and receive?

Better? You are relying too heavily on anecdotal reports.

For one, I seriously doubt you compared a 75M vertical dipole to a 75M
horizontal dipole in your lecture - no one in your audience would have
the financial clout to go there I suspect. That vertical dipole tip
would have to be hoisted quite a distance to see that the bottom tip
wasn't buried in the earth.

The next problem is height (again) and how it contributes to (or
subtracts from) gain as that varies. There is no "similar" comparison
between the two. You could model and present variations on horizontal
dipole elevation alone for two hours, much less both of them.

Rule 1 of presentations: Don't give them off the cuff unless you are
prepared to follow the surprises.

Rule 2: If you are willing to follow the surprises; then you aren't
really giving a presentation.

73's
Richard Clark, KB7QHC