Richard Fry wrote:
On Dec 22, 11:13 am, "Frank" wrote:
In this example the vertical half wave dipole, with the base 30 ft above
an average ground, on 147.3 MHz, shows a field strength at ground
level of: 0.418 uV/m from 30 W into the antenna.
And, obviously, at 50 km.
________________

Here is another method (Longley-Rice) for calculating the field
intensity produced at the receive site by your model. But the NEC
approach is less accurate than L-R for long path lengths (due to earth
curvature), and for specific terrain contours.



Once you get away from the near field, there's tons of models and
modeling approaches available, depending on the kind of path you're
interested in, and what you're looking to find out. For instance,
ioncap and its ilk (VOACAP,etc.) model skywave paths in a statistical
sense. Other models do raytracing for a more "point solution" type
model. Yet others are good for things like forests or terrain.

Since nobody has a full up computed electromagnetics finite model of
everything at fine resolution, all those models basically trade off
computational resources against some approximations. Whether it's
approximating the earth as flat surface of a uniform dielectric (NEC)
or whatever..