Dave,
I saw your note and question and would like to add a few remarks.
The idea of ducting being responsible for 160 meter propagation is mainly
as a means of getting signals to great distances (largely loss-free within
the duct). And there's nothing mysterious about the duct; it's there at
night and seen by all the incoherent scatter radars that probe the
ionosphere.
The duct (electron density valley between the E- and lower F-region) is
probably "leaky" so what you get out is a fraction of what went in. Some
of the RF may leak out after shorter E-F hops. But that is signal
strength, not direction.
For ionospheric refraction, whether in the vertical or horizontal planes,
the important thing is the variation of the electron density with
position. Normally, our earth-ionosphere hops result from the fact that
the electron density increases with altitude. And RF sent upward is then
REFRACTED AWAY from regions of higher ionization. That is theory of a
general nature.
The skewing of paths follows the same principles so whenever you note a
skewed path, you should realize there is a horizontal gradient in
ionization along the path. But "Where and How?", that is the $64 question.
Auroral ionization would be a prime source for skewing on Top Band as
most interesting DX paths go across polar latitudes. But looking at your
dark path around 2300-0000 UTC, one would think that RF from Heard would
be refracted AWAY from the more intense ionization that's west and along
the terminator. That suggests to me that RF reaches you from a more
southerly direction and may be sneaking in the back of your Beverage.
I know people are very defensive of their Beverages and I do not want to
rub them the wrong way. But I think they do have a finite F/B ratio that
varies with RADIATION ANGLE. So that is the serious idea that I can come
up with, short of invoking some wierd, unnatural distribution of
ionization.
The only other idea that I heard about was to the effect that Romeo was
out there again, pulling Top Bander's legs, but I seriously doubt that too.
73,
Bob, NM7M
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