On 3/23/20 10:05 PM, Dan Maguire wrote:
Grant wrote:
If you really want to know the parameters, see antennasbyn6lf.com as Rudy
describes techniques for ground RF properties measuring.
Turns out that very subject was being kicked around on a recent qrz.com thread:
https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/
Dan, AC6LA
This was pretty well studied by George Hagn at SRI in the 60s/70s in the
context of antennas for field use of HF and VHF in Vietnam and there are
some publications out there. In fact, that's what led to the development
of the Open Wire Line (OWL) technique.
The problem with a dipole measurement is that it measures a large area,
and the answer you get is some unequally weighted average of the
properties of the soil under the dipole. I can't remember if it
effectively weights the ends or the middle of the dipole more heavily.
The other problem is that it is affected by surrounding vegetation (i.e.
anything within the near field potentially affects the numbers). That's
generally a smaller effect except in dense forest or jungle, and one can
argue that what you're really looking for is a number to plug into a
model for "environment"
That doesn't make it a bad technique, but one needs to understand what
you're actually measuring and to what use you're going to put the
numbers you've calculated.
For instance, if you're setting up a phased array, and you want to
calculate Mutual Z (rather than measuring it) - you typically need soil
properties on a finer grid.
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