Polarization - As Jerry K4SAV stated, the electron gyro-frequency plays an
important role on 160m since our ionosphere is immersed in a magnetic field
- it also affects ionospheric absorption and refraction. For those of us at
mid to high latitudes, vertical polarization on 160m is *theoretically*
optimum since it couples the most energy to the limiting polarization at
the entrance to the ionosphere. I don't understand Mark K3MSB's comment
about the polarization terms disappearing unless it has to do with that
fact that the polarization going up to the ionosphere has nothing to do
with the polarization going thru the ionosphere (which is dictated by the
ionosphere).
Elevation angles - Ray tracing shows that elevation angles up to about 10
degrees are E hops since there is still enough E region ionization at night
to refract 160m. I don't know how important these E hops are - probably
okay for short distance, but the losses (absorption and ground reflection)
add up quickly for the longer distances. Above 15 degrees or so we get F
hops. From 10-15 degrees is where ducting occurs in the electron density
valley above the nighttime E region. Ducting in the valley likely requires
shallow angles. But when a signal gets dumped out of the duct, that
suggests a higher down-coming angle.
K4SAV said it best: ". . . and the real world on 160 is very complicated."
Carl K9LA
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