Reg, G4FGQ wrote:
"On the other hand, a simple vertical does reasonably well when working
just across country because of the short propagation path, almost
straight up and down again, even via the groundwave for a very short
distance."

True, but the thread is: "Verticals versus Horizontal Dipoles". Reg`s
choice, I think.

Verticals have a null toward the zenith which tends to impair their
"straight up and down again" performance. The horizontal dipole`s nulls
are at its tips, too, but are pointed elsewhere, not at the zenith. This
mey actually avoid some noise and interference beyond that originating
in the directions of straight up or down again. As much noise is
vertically polarized, it may be rejected by ctoss-polarization.

The horizontal dipole performs pretty well in the directions near the
zenith when it is elevated at less than 1/2-wavelength in height, and
for frequencies below the maximum usable frequency at near vertical
incidence. At 1/2-wavelength elevation, the horizondal dipole develops a
null toward the zenith, too.

Propagation of H-F signals via the groundwave is for a very short
distance indeed. Frequency has a pronounced effect upon sffective earth
conductivity. Conductivity falls fast with increasing frequency due to
skin effect. . The earth layer penetrated by the wave thins as frequency
increases, making it less conductive and increases loss. For example,
over soil of 10 mmhos/m, a fairly common value, a transmitter would have
to ptoduce 1,000 times more power at 5 MHz to produce the same signal at
10 miles as would a 0.5 MHz transmitter.

The earth`s attenuation of low-angle radiation from a 1/4-wave vertical
antenna has a significant effect on the vertical radiation pattern. ee
Fig. 54-1 on page 465 of B. Whitfield Griffith`s "Radio-Electronic
Transmission Fundamentals". This figure shows field intensity curves
versus vertical angle from a 1/4-wave vertical antenna radiating 1
kilowatt over earth of average conductivity. Anything below about
5-degrees is gone, eaten by the earth`s losses.

I conclude that for high frequencies, unless you have good or very good
conductivity soil, horizontal polarization will likely serve you better
than vertical polarization.

If you are at sea or immediately on the sea shore, you likely may do
better with vertical polarization.

There are so many variables that it would likely be best to have
antennas of both polarizations available, and to use the antenna which
gave the best signal in the particular instance.

Best regards, Richard Harrison, KB5WZI