W7EL wrote:

So even at 10 km distance from the antenna at 3 MHz over average ground,
the sky wave is more than 60 dB stronger than the surface wave. The
difference becomes greater at higher frequencies and greater distances.
This is why the surface wave is of little practical interest to most
amateurs. And it's why you'll never see the wonderful low-angle
ionospheric propagation effects Rich predicted in his original posting
on this thread.

Surface wave applies mostly to day time propagation at AM band and 160.
When we propagate during the night at low bands, horizontal (high angle)
antennas give stronger signals within about 500 -700 miles. Beyond that the
low angles (surface?) rule, except in some high angle propagation at
sunrise. Those who work long pass and far DX on 160 know that verticals (low
angle) dominate (while being "inefficient" at closer distances at the same
time). Being at the salty beach front enhances the signals and low angles by
about 10 - 15 dB. Can we call those angles "surface"?

The point is that propagation modes are very finicky and vary, making blank
statements about attenuation some times doesn't jive. Way back when
scientwists figured out that no way signals on HF can go large distances,
because of calculated dispersion etc. we (OK, our forefathers) were given
"useless" HF bands to play with.

The EZNEC/4 results are just what we should expect, given a knowledge of
how the surface wave and sky wave are attenuated with distance.

That is somewhat valid within close proximity (one "hop").
EZNECs do not incorporate propagation mechanisms. They are usefull to
calculate the pattern of particular antena, but how that fits the
propagation and delivering the signal to the target, is another story. Most
people trivilialize the propagation and assume that signals nicely bounce
between the ionosphere and earth, which in reality gets way out of those
distorted pictures of earth-ionosphere in the books.
http://members.aol.com/ve3bmv/bmvpropagation.htm

I caution people to take care in extrapolating propagation or antenna
performance results at AM broadcast frequencies to the higher
frequencies more commonly used by amateurs. If done carelessly, it can
lead you to reach some pretty seriously wrong conclusions.

That applies also when trying to use EZNECs and other antenna modeling
software in predicting propagation and how the signals get to the other end.
The beautifull and unknown thing is that propagation can play games with
paths of signals and unless one has variety of antennas that can "see" the
angles and modes, you would never know.

Roy Lewallen, W7EL

Just an example: I was at Cape Hatteras on 10m in a contest. Band started to
open and ZS6EZ told me I was the only NA station he was hearing. Was that
"dead" surface wave? It was definitely low angle from my pair of verticals
stuck in the sand and running barefoot. Big multi/multis with their stacked
beams and kWs were not audible, and they CQ even on the dead band. The point
is that I was "manufacturing" signal at low angle, that according to
calculations should have been "expired".
Another one was when operating 160m from W8LRL. There was short opening to
Japan. Wal has different antennas for that area. Vertical circle 8 el.
array, EWE, regular Beverage, phased Beverages and 3.5 wave long Beverage.
JAs were audible only on 3.5 wave one, which has the lowest angle than any
other antennas.
Obviously, low angles are not useless for DX as above calculations might
imply.

W8JI way back argued with me that there is no way there could be high angle
propagation from long haul DX on 160, or skewed path. (Now he is the guru on
the subject :-) At he sunrise, low (high angle) inverted Vee can run
circles around verticals and Beverages. The difference could be dramatic,
like S7 vs. no signal.
I discovered way back than one has never enough of antennas, especially for
serious contesters, if they want to take advantage of different propagation
modes and angles/polarizations.

73 Yuri, K3BU, VE3BMV etc,.