The link in the opening post of this thread shows an interesting, animated
analysis of the elevation gains of a monopole, based on a NEC far-field
analysis not including the surface wave.
I then posted this comment, "Reality is that radiation leaving the monopole
at elevation angles of at least 5 degrees decays at a 1/r rate. Therefore
that radiation is a space wave which propagates in a ~ straight line to
reach the ionosphere, where (with suitable conditions) it can return to the
earth as a skywave."
Others have been skeptical that this low-angle radiation was a space wave
that could reach the ionosphere.
Recently I investigated this more closely, leading to the NEC4.2 study
linked below. It shows that the 3.8 MHz radiation existing on a departure
angle of 5 degrees at a distance of 3/10 of a mile from a monopole continues
on toward the ionosphere along that path, while its value decays at a 1/r
rate -- indicating that it is a space wave.
http://s20.postimg.org/6yau4m225/Monopole_Radiation_5_deg_Departure.jpg
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