Topband: verticals by the sea

[Richard Fry]

NEC modeling to determine the effects on the fields radiated by a vertical 
monopole when siting it near a salt-water coastline can be highly misleading 
if the surface wave field is not considered.

For example, the plots linked below show that for average earth conductivity 
the E-field at 5 degrees elevation is about 2.44 times greater in the 
surface wave plot than in the far-field plot, at the same horizontal 
distance from the radiator. Their difference is infinite in the horizontal 
plane.

But if this radiator was sited 1 km from the ocean, then the fields at 1 km 
shown in the surface wave plot would decay at nearly a 1/r rate as they 
propagated further on that bearing, along and over the ocean surface.

This is a much different conclusion than reached when considering only the 
NEC far-field analysis.

Comment/discussion is invited.

R. Fry

http://s24.postimg.org/6nchfpt1h/NEC_FF_vs_NF_Calcs.jpg