I'm weighing in with Tom here. The reciprocity theorem in electromagnetism
is well known, and it shows that no amount of focusing, defocusing,
scattering, refraction, or reflection will by themselves cause one way
propagation. If you take away the earth's magnetic field and its attendant
Faraday rotation, I do not see any other reason for one-way propagation if
noise levels at both ends of the path are equal.
See
http://en.wikipedia.org/wiki/Reciprocity_(electromagnetism)
and
http://en.wikipedia.org/wiki/Faraday_effect#Faraday_rotation_in_the_ionosphere
.
73, Carl WS7L
Tom,
>
> It is a known that the ionosphere is not a perfect sphere. It is always
> moving and it is lumpy and tilted. Together these occurrences can cause
> focusing and defocusing of the wave due to deformities especially if they
> are concave or convex. One-way-propagation can reveal itself as a deep
> and/or prolonged fade on only one end of the link because of the
> aforementioned reasons. Of course fades can be caused by other reasons,
> such as multiple paths, etc.
>
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