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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: (
Date: Fri, 20 Jul 2001 13:20:26 +0200
Just a series of thoughts ...
In case of horizontally polarized antennas placed at a reasonable 
height, the ground costants have a neglegible impact on the radiation 
pattern and efficiency, while the model should better take in account 
the soil profile rather than conductivity or dielectric constant.
In case of vertically polarized antennas I've instead some doubts on 
results and reliability of common amateur software over poor 
conductivity media, either because of inefficient ground slope modeling 
and also because of electrical discontinuities between different soil 
Expecially in case of vertically polarized antennas infact, what's 
exactly below the antenna can be always overcome by an artificial 
ground made of radials or screens (in term of losses) but what's far 
away is instead what determines if and how there will be reflection, 
refraction or absorbment at a stated frequency.
In the case one believes to be in an area with constant ground 
parameters, than any measure or chart can be a good choice.
The noticeable advice that a soil practically good on 1.8 Mhz can be 
instead rather awful a few octaves above is surely something to keep in 
mind when modeling, and not only when evaluating the ground by 
measuring impedance on a sampling horizontal antenna at different 

Mauri I4JMY

> ---------- Initial message -----------
> From    :
> To      : <>, <>
> Cc      : 
> Date    : Thu, 19 Jul 2001 22:44:02 -0400
> Subject : Re: [antennaware] question on ground system for good ground
> NEC-2 should work down to a very low height (inches).  If you want to 
> 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
> patterns.
> 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. 
> ledge just South of the tower).  Localized conductivity is less than 
1 mS/m.
> 73, Gary
> K9AY
> ----------------------
> From: "Eric Scace K3NA" <>
> >    The choice of elevations to make measurements is frequency 
> 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 
> but know that there is some point which is "too close to
> > ground" to give accurate results.  The "low" height should be above 
> 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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