Thanks to everyone for your comments on polarization. I certainly agree with Tom W8JI in that this discussion is a brain exercise (he also said enjoyable). It forces me to delve deeper to asses whether I have a screwed-up understanding of all of this. And he has a good point in that this is a system analysis.
It also seems to me that polarization in the ionosphere is a bit fuzzy to many people. First, an HF electromagnetic wave upon entering the ionosphere splits into TWO waves that propagate thru the ionosphere - one of these characteristic waves is called the ordinary wave and the other one is called the extraordinary wave - they rotate in opposite directions - and the polarization ellipse at HF for both is pretty much circular (a special case of an ellipse). On MF, the polarization ellipse tends towards a thin ellipse - with the ordinary wave essentially being vertically polarized since the major axis of the ordinary wave is parallel to the magnetic field lines at these latitudes - which in general dictates vertical polarization on 160m at mid to high latitudes in the northern hemisphere. Did anybody note the signal difference between OH8X's horizontal Yagi (before it came down, of course) and a vertical (or 4-Square) also in OH-land? Second, the magnetic field dictates that only two characteristic waves can propagate in the ionosphere - and as I said above they are pretty much circularly polarized at HF. Chapter 3 of "Ionospheric Radio" goes thru the math that shows this (equation 3.7). Again we're talking about waves that propagate in the ionosphere. Of course the polarization of the wave from your antenna to the entry point of the ionosphere is that of the antenna - and it should be very constant until it enters the ionosphere. So the job of your transmit antenna is to deliver the most power at the azimuth angle dictated by the ionosphere, at the elevation angle dictated by the ionosphere, and at the polarization that couples the most power into the characteristic wave (ordinary or extraordinary) that is propagating best thru the ionosphere. Tom asked "What ratio of V to H signals levels do you expect?" I can't answer his question as it's really an ellipse - not a V component and H component. What I can say is on 160m, from my work with the PropLab Pro ray tracing software, I would expect the ratio of the major axis to the minor axis of the ordinary wave's polarization ellipse when it comes out of the ionosphere to be in the neighborhood of 2.5 (the major axis length is 2.5 times the minor axis length). For reference, circular polarization would be a ratio of 1.0 (both axes are the same length). That's enough for now. This is interesting stuff for sure (at least to me!). Carl K9LA _________________ Topband Reflector Archives - http://www.contesting.com/_topband
