Topband: Elevated Radials

Richard Fry rfry at
Wed Mar 6 10:06:48 EST 2013

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. 

More information about the Topband mailing list