A common use for correctly defined NEC models shows the electrical characteristics of the radiator system itself. But NEC also will show the field intensities that system will produce at a given distance for a given applied power, frequency, and earth characteristics -- and do so quite accurately. The link below leads to a comparison of the groundwave field measured from a real-world AM broadcast system by a broadcast consulting engineering firm vs. the NEC-2D output using those same system parameters.
Included in the NEC analysis is the value of the space wave field at an elevation of 100 meters above the (level) ground plane, for this installation -- which should help better understand the points of the opening post in this thread. Note that the value of the space wave at 100m elevation and 100m downrange is lower than the groundwave 100m downrange, and increases as the range increases. This is as expected, because the relative field (E/Emax) of the elevation pattern "launched" by this 1/4-wave monopole reduces as the elevation angle increases. Hope this graphic and explanation are useful. http://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
