jim Jarvis wrote:
> I wasn't going to comment on this, because wiser heads have
> prevailed, on this topic,
> for the most part.
>
> HOWEVER, I learned something today that may be worth contributing to
> the discussion:
>
> I have always assumed that fading was principally a result of changes
> in arrival angle,
> due to ionospheric dynamics, and accepted the literature which said
> that all signals arrived
> horizontally polarized. This morning, I learned that it may be
> polarization that is the principal
> variable.
>
> At k2ttt's place, getting my taxes done, we were playing with his new
> K3, and discussing the
> impact of having dual receivers. This past season, on 160m, he had
> an inverted vee, horizontally
> polarized, and a loop, which was fed to be vertically polarized.
>
> By putting one antenna into each receiver, he was able to observe
> that the principal variable
> seemed to be polarization. Selecting diversity receive, he had dead
> solid signals, when either of
> the individual channels was fading to the point of no copy.
>
>
There's been a lot of work in the literature on implementing very
reliable HF data links, and polarization diversity on receive is almost
always an essential component. Your observations fit in with both the
theory and the empirical data. In fact, it turns out that you don't
really need to obsess about having two orthogonal antennas, since the
polarization for HF antennas close to the ground is pretty funky and has
lots of wiggles and bumps. A typical receive setup in the literature
combines a short vertical and a small loop, or a couple loops in
different orientations.
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