Richard Fry wrote:
"Roy Lewallen"
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.
___________

Roy, didn't the experiments of Brown, Lewis & Epstein of RCA in ~1937
show that the h-plane field measured 3/10 mile from a vertical monopole
of about 60 to 88 degrees in height, over a set of 113 buried radials
each 0.41 WL, was within several percent of the theoretical maximum for
the applied power as radiated by a perfect monopole over a perfect
ground plane? And conductivity at the NJ test site was poor -- 4 mS/m
or less.

That tends to show that the fields radiated at very low elevation angles
also will be close to their theoretical values when measured at this
radial distance, even though ground conductivity at the antenna site is
poor. The relative field (E/Emax) for radiators of these heights and
propagation paths approximately equals the cosine of the elevation angle.

I believe we've discussed this before, so I'll be brief.

Their calculation of the field at the receiving site when the radial
system is perfect was adjusted for the effect of ground wave attenuation
caused by the imperfect ground conductivity. If the ground between the
antenna and receiving site were perfect, the field strength would have
been greater.

Also, I'm speaking of sky wave. Ground reflection isn't a factor in
determining surface wave, which is what they measured and which isn't of
interest to most amateurs.

The greatest radiated fields always will be directed in or near the
horizontal plane when measured/calculated for such conditions. This
also will be true for any monopole from infinitesimal to 5/8 wavelength
in height, although the elevation pattern of monopoles from /4- to
5/8-WL no longer are described by the cosine function (see
http://i62.photobucket.com/albums/h8...omparison.jpg).

Elevation patterns show maximum relative field centered at various
elevation angles above the horizon, when those fields are measured at
progressively longer radial distances from the monopole, due to the
propagation loss for the surface wave over other than a perfect, flat,
infinite ground for those ranges. Earth curvature and terrain
diffraction add to those losses for longer surface wave paths over real
earth, and for very great distances the h-plane relative fields falls to
~zero.

As I thought you were aware, the surface wave propagates considerably
differently than the sky wave.

But that pattern shape is not the pattern shape originally radiated by
the monopole, it also includes the effects of the propagation
environment at the range where it was measured (or calculated).

If this were not true then MW broadcast stations would have essentially
zero coverage area for their groundwave signals.

It would be a mistake to design HF antenna systems based on optimizing
surface wave propagation as AM broadcasters do, unless you desire
communication for distances not exceeding a few miles.

Roy Lewallen, W7EL