RE: Capability of NEC for Accurate Modeling of Groundwave Fields Close to a
Monopole using Elevated Radials
As an example...
The FCC groundwave propagation chart for 1490 kHz (Graph 18-A) shows that
the field at 1 km over 1 mS/m earth is 51% of the inverse distance field.
The inverse distance field is the field existing for a perfect ground plane.
The reduction for real earth paths is due to propagation loss over less than
perfect earth.
Going back to my NEC model of a 1/4-wave monopole driven against 4 x
1/4-wave elevated radials, I changed the ground type from perfect to a
conductivity of 1 mS/m. The NEC-calculated field at a distance of 1 km for
1 kW of applied power dropped from 313 mV/m to 160 mV/m, which is a
reduction to 51% of the field for a perfect ground plane.
NEC is quite capable of giving us the correct answer, when it is asked the
right question.
_________________
Topband Reflector
