Walter Maxwell wrote:
Roy, W7EL wrote:

I haven't looked into this carefully, but one person I know who was very
involved in NVIS operation (where ground characteristics are important)
tried it some years ago. He concluded that it wasn't possible to
set the antenna height and make measurements with sufficient accuracy to
infer the ground characteristics with any confidence.

Roy Lewallen, W7EL


Understood, Roy, but was this person saying that with just one height it
wouldn't give sufficient accuracy, or is he saying that with impedance knowledge
at many different heights there would still be no determination of any of the
ground characteristics?

I interpreted what he said as meaning that he looked into the method and
determined it wasn't practical. Surely he thought of making numerous
measurements. He's a very capable engineer, so I took what he said at
face value. On the other hand, I don't think he's highly skilled in
making precision antenna measurements, so he might have assumed that a
level of accuracy wasn't achievable which in fact might be.

You might spend a little while with EZNEC looking at how much a change
in ground conductivity or permittivity changes the antenna input Z at
various heights, and how much the height changes the Z with a given set
of ground characteristics. Then consider whether you'd be able to set
the height and make the impedance measurements accurately enough to
infer the ground characteristics with any degree of confidence.

Would you not like to see my data before concluding it couldn't reveal any
ground characteristics.?

I'd like to see your data, but it wouldn't be enough information to
conclude whether the method would be practical or not.

Roy Lewallen, W7EL