[Antennaware] Testing the theory..

Guy Olinger, K2AV olinger at bellsouth.net
Thu Mar 29 18:45:34 EST 2007

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 

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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