NEC-2 should work down to a very low height (inches). If you want to model
the antenna on or under the surface, you'll need NEC-4!
Eric is right about frequency dependence -- my own trial was at 40M. I was
forced to figure out the conductivity in order to tune a 40M beam at 25 feet
and get it to work as desired at 75 feet. The data correlates acceptably on
80 and 160; I changed Beverage terminations and obtained much cleaner
By the way, the FCC graphs show this area (30 mi. East of Atlanta) to have a
conductivity of 2 to 4 mS/m. Under my station, there is zero to a few feet
of red clay on top of granite bedrock (I have an exposed 40x100 ft. granite
ledge just South of the tower). Localized conductivity is less than 1 mS/m.
From: "Eric Scace K3NA" <firstname.lastname@example.org>
> The choice of elevations to make measurements is frequency dependent.
Pick a "low" and "high" height that are appropriate to the
> frequency band being considered.
> I'm not personally familiar with the computation limitations for NEC-2,
but know that there is some point which is "too close to
> ground" to give accurate results. The "low" height should be above any
such limit for the calculating engine.
> Lastly, don't be surprised if ground characteristics are different for
different bands. RF penetration can be frequency
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