Hi Mike,
> Are you suggesting that signals arriving from the ionosphere at
> moderate to low elevation angles are predominatly vertically
> polarized? I was always led to believe that they were basically
> randomly polarized and that the polarization was time varying
> to some degree.
That is my understanding also, although without an airplane or
balloon I don't how to confirm it at very high heights.
I can understand how the earth modifies the
> pattern of an antenna (the reflected versus direct waves add or
> subtract depending on their relative phase), but please explain
> to me how the earth modifies the polarization of an incident
> wave independent of the antenna?
I guess it is like the paradox about a tree falling in the woods or the
chicken and the egg. While the earth certainly does not change the
arriving wave, within a small fraction of a wavelength any low angle
horizontal component is cancelled by re-radiation from the earth.
So what does it matter if we consider it an antenna pattern
problem, or a "signal" problem? The result is response to low
angles is not there. It is a good demonstration of reciprocity, and it
illustrates how difficult is to tell what is coming down from the sky
when we are trying to observe it near earth.
All that aside, I think if there was a significant higher angle
component (say above 30 degrees) at modest or long distances
my low dipole and high dipole would better than the vertical. Either
the low angle signal of my vertical is much better than modelled, or
the wave angle generally very low, or both. I wish there was a way
to tell which was true, but at least I know the wave angle is
definitely not high.
73, Tom W8JI
W8JI@contesting.com
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