Tom W8JI said
<It is only at sunrise I find the dipoles useful, approaching or even
beating a vertical. The question is WHY are they better. Is it polarity
or wave angle? I suspect wave angle and probably not polarity, but it is
only a guess.>
Don?t count out polarization, Tom. Remember that British IEE paper I
sent you? Although the limiting polarization for those of us in North
America is predominantly vertical (which means the polarization exiting
the ionosphere going down is predominantly vertical and going up vertical
polarization couples best into the ionosphere), steep gradients of
electron density can cause this predominantly vertically polarized
ordinary wave to excite the extraordinary wave, which would be
predominantly horizontally polarized. And of course there are steep
gradients of electron density at sunrise.
I?m not saying this is the why the dipole is stronger at sunrise - it?s
just a possibility that needs some good controlled observational data to
prove or disprove (perhaps using a vertical over salt water, a vertical
over average ground, a low horizontal dipole, and a high horizontal
dipole - one hell of an experiment indeed). Maybe it is angle. I don?t
know. But I do know that there are some pretty interesting things
happening at 1.8MHz due to the Earth?s magnetic field that usually can be
ignored on the higher HF bands. This interaction of the Earth's
magnetic field with 1.8MHz energy results in interesting things
happening with the refractive index and with polarization (and
absorption).
And another thing that clouds the issue - many of our antennas have a
response to the other polarization. For example, Beverages respond to
horizontal polarization off the side. This certainly doesn't help clear
up matters.
Carl K9LA
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