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.
-- Eric K3NA
-----Original Message-----
From: owner-antennaware@contesting.com
[mailto:owner-antennaware@contesting.com]On Behalf Of Gary Breed
Sent: 2001 July 18 Wed 23:45
To: antennaware@contesting.com
Subject: Re: [antennaware] question on ground system for good ground
Here in the U.S., the simplest way to get an estimate of regional
ground conductivity is from the records of a nearby directional
(multi-tower) AM (medium wave) radio station. Their operating
parameters are based on field strength measurements that are
correlated with established ground conductivity curves. I don't know
if there are equivalent field strength measurements routinely made by
European MW stations.
An alternate experimental approximation would be to make a
dipole and measure its impedance at a low height (3 to 5M), then
raise it to 15-20M and measure it again. I was able to determine
that the ground under my antennas is lower conductivity than
expected from broadcast data simply by measuring the change in
resonant frequency (R +j0) at two heights. Select various values
for conductivity in your modeling program until the model matches
the measured data. I use EZNEC with the NEC-2 engine.
73, Gary
K9AY
>
> From: "Henk Remijn" <hremijn@zeelandnet.nl>
> To: "Antennaware" <antennaware@contesting.com>
> Subject: question on ground system for good ground
To: <antennaware@contesting.com>
> Date: Wed, 18 Jul 2001 22:20:52 +0200
>
> Hi,
>
> I want to model some antennes but I am stuck with what ground type to
> choose.
> The place the antennes are is on a place which was before 1850 salt
> water.
> since then there is land.
>
> What I like to know, how can I measure or calculate the ground
> resistance of
> a location.
>
> Is there somebody around who can help me on this or who can give me some
> good links to info.
>
> 73, Henk PA5KT
>
>
>
>
> --
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>
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