Tom,
In response to your question about why the polarization is dependent on
the direction of the wave relative to the earth?s magnetic field, it
looks like NM7M beat me to the punch (heavy sigh - the luxury of being
retired). There?s not much more I can add, except to talk about NM7M?s
reference to the work of the BBC engineers in ?65.
What he?s referring to is an IEE (out of the UK) paper by Phillips and
Knight titled ?Effects of polarization on a medium-frequency sky-wave
service including the case of multihop paths?.
What this paper does is derive the limiting polarization for an ordinary
wave exiting or entering the ionosphere. The main feature of the paper
is a graph of the orientation of the polarization ellipse vs magnetic
bearing of the wave and magnetic dip angle. This is just the graphical
presentation of what NM7M is talking about and what VE7FPT summarized a
week or so ago.
It?s easy to see from this figure that for those of us in the US,
vertical polarization is the way to go. But if you?re near the
geomagnetic equator, you better think about horizontal polarization for
essentially anything except north-south paths.
Carl K9LA
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