K9AY wrote:
> In the near-field, A/B comparison measurements on a simple antenna
> like a
> vertical would normally be valid, but not necessarily so with
> changes to the
> ground system. The change in the surface wave (ground wave) can be
> different
> from the change in skywave.
What I have never seen documented is actual measurements of far-field
sky-wave changing with numbers of radials, along with the
corresponding measurements at the ground. Sky-wave has always been by
inference, such as how much field is theoretically "available" with a
given power level at the feed, given some "ideal" situation. All had
one assumption or another at root, with one's confidence in the
assumption propagated to the inferred sky-wave.
It always seemed to me that some very tall non-conducting structures,
or the likes of a helicopter and GPS or some strict, accurate
positioning method for the helicopter would be required to document
the ground/skywave correlation.
Since the commercial and regulatory interest at MF was
millivolts/meter at the ground, there doesn't seem to have been much
motivation.
It's not the sky wave that I would suspect as quirky, but real ground
is subject to such variation as might give some kind of non-linear
result with increasing radials that would not appear in the skywave.
20 degree skywave at a distance of one mile (~10 wavelengths at 160m)
would require an elevation of 1922 feet for the measurement.
There may be some directly measured data out there, but I have never
seen it, and would love to see the citation if it exists.
73, Guy.
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