It's not how low a frequency, it's how high. "Faraday rotation" describes a
more or less steady rotation of a radio wave's E (and H) field as that wave
is propagated.
Faraday rotation is a result of electrons orbiting their nuclei at an
"electron gyro frequency " under the influence of the Earth's magnetic field.
The electron gyro frequency is something between 600 khz and 2.4 mHz,
depending on the location and the instantanious level of the magnetic field.
The wave polarization at the recieving antenna depends on the intensity of
the Earth's magnetic field, the electron gyro frequency, the frequency of the
desired signal, and the path length. Any change in any of these factors can
shift polarization 90 degrees - and cause an almost total fadeaway.
The textbook electron gyro frequency is 1.8 mHz for the northern hemisphere,
but it varies with latitude.
The closer a given frequency is to the egf the more effect it has. Therefore
Faraday rotation is greatest on 160, a bit less on 80, less yet on 40, etc..
It does occur on 10 when the magnetic field is agitated, and I have been told
it sometimes occurs on 6. But I have never seen that. And I would take any
reports of Faraday rotation on two meters and up with a bucket of salt.
73 Pete Allen AC5E
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