To All from PA0SE
Jim, M0MBU, wrote:
Software such as EZNEC gives the result that there is
zero propagation along the horizontal with anything other than
perfectly conducting ground, but we all know this is not so.
That is so because the program does not compute the surface wave.
Maker Roy Lewallen, W7EL, wrote to me:
"'Only the professional versions of EZNEC (EZNEC-M and EZNEC/4) directly
report the ground wave. However, a reasonable approximation of the ground
wave strength can be gotten by using the EZNEC near field analysis. This is
because the "near field" analysis actually calculates the total field, both
near and far, including the ground wave. The near field analysis results are
available only as numbers; they are not plotted as a graphical pattern".
I found out that the same applies to the program AO by K6STI that I use.
In the region where field strength of the ground wave decreases in a linear
way with distance the ground wave fills the area between the pattern lobe
presented by EZNEC or AO and the surface and the result resembles the
pattern that the programs (and text books) show as the vertical radiation
pattern of a short vertical antenna over perfect ground.
73, Dick, PA0SE