[TenTec] Even MORE on vertical antennas!

AC5E@aol.com AC5E@aol.com
Tue, 3 Sep 2002 18:25:27 EDT

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