Topband: Modeling "Ground"

[Richard Fry]

In reality, NEC4 can produce quite accurate results when modeling buried 
radial wires and groundwave propagation losses along a real earth path -- as 
long as earth conductivity is known for that path and operating frequency.

The link below shows the value of the groundwave E-field at a range of ~28 
miles produced by a NEC4 model of an AM broadcast station.  Even though NEC 
does not account for earth curvature, this groundwave path is short enough 
for that error to be negligible.

The NEC field is rather a close match to the value shown for this set of 
conditions when using the FCC's groundwave propagation curves for this 
frequency, radiated power and earth conductivity (see the table at the 
bottom of the graphic).

http://s20.postimg.org/tkg5hcfsd/WLS_NEC_vs_FCC_Field.jpg

R. Fry, CPBE