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[antennaware] question on ground system for good ground

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Subject: [antennaware] question on ground system for good ground
From: Gary Breed" < (Gary Breed)
Date: Thu, 19 Jul 2001 22:44:02 -0400
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.

73, Gary

From: "Eric Scace K3NA" <>

>    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
> dependent.

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