Just to note that the low-angle radiation produced by monopoles is not
accurately shown by a NEC model/study that does not include the surface
wave, regardless of whether one or two ground-plane media are specified in
the model.
Below is a link to a NEC study of the low-angle fields of a monopole
__including the surface wave__ for three values of earth conductivity
ranging from extremely good to very poor.
The curves there all show maximum relative field in the horizontal plane.
If the surface wave had not been included in these studies then all of those
fields would have a zero value in the horizontal plane, and reduced fields
at low angles just above the horizontal plane.
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.
NEC analyses of a vertical monopole of 5/8-lambda and less, and not
including the fields of the NEC surface wave do not recognize the radiation
sector capable of producing the greatest single-hop skywave service range
that can be provided by that monopole.
http://s20.postimg.org/9xqgzu9d9/Monopole_Low_Angle_Radiation.jpg
R. Fry
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