Topband: gyro frequency

Carl K9LA
Mon, 23 Apr 2001 21:04:52 -0500


> can you explain what should happen, and
> why, with propagation of radio waves
> around the electron gyro frequency?

In the December 2000 issue of the Low Band Monitor, I explained
absorption and the electron gyro frequency.  It showed how absorption
varied between the ordinary wave and the extraordinary wave, and how it
varied based on the angle between the direction of the propagating wave
and the magnetic field.  In the future I plan to do the same for the
index of refraction.  And probably polarization.  I'm not sure many are
really interested in these topics (I think I caught NM7M's attention,
though), but I personally think it's some neat stuff that makes 160m
very, very unique.

On 3.5MHz and higher it's pretty safe to assume that absorption, etc, is
independent of the angle between the magnetic field and the direction of
travel of the propagating wave.  That really simplifies things, and
makes propagation predictions on 80-10m much simpler.

Not so on 160m.  As our operating frequency approaches the electron gyro
frequency (160m is getting real close), absorption, etc, is very
dependent on that angle.  That's because electrons aren't sitting still
up there - they move in a spiral motion around magnetic field lines, and
are influenced primarily by the orientation of the passing wave's
electric field.  I think this is the main reason why our propagation
prediction programs (except for Proplab Pro) do not address 160m - they
do not take the dependence of that angle into account because it's too

For all the details and mathematical derivations (and there's a lot of
math in there), I think Ratcliffe's book (The Magneto-Ionic Theory & Its
Applications to The Ionosphere, 1962) is the way to go.

As I said earlier, I think 160m is very unique compared to all our other
bands.  There's still a lot that's not understood, but that's what makes
it such an intriguing band.

Carl K9LA

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