[amsat-bb] RH or LH ??

[James Jipping]

Good Morning!  Just reviewing some past email and the topic of which 
polarization "RH or LH ?" showed up.

It must have been close to a solar activity maximum that I started my 
satellite adventure.  Faraday rotation was in full swing (or should I 
say "rotation").  It was a phenomenon we all experienced and had to deal 
with.

My first antenna project included a polarization switch  and I have 
always had one on my satellite antennas.  My arrow linear polarized 
antenna has one  (my arm/wrist rotation device).  I would like to advise 
that if you can manage it (financially or creatively -- "in the good old 
days it was creatively")  to include some way of changing the 
polarization plane or direction of both the transmitted and received wave.

ALL signals WILL experience some amount of polarization depending on the 
strength of the earth's magnetic field strength IN THE PATH of the 
signal from station to satellite (and vice/versa).  The total rotation 
effect is constantly changing.  And do not forget the effect that the 
earth's ionosphere has on polarization.  As we know, the ion density of 
the ionosphere, is constantly changing.  Right now that effect is at 
it's minimum as the sun's sunspot activity is at it's minimum.  IT WILL 
change and the effect will really begin to be noticed.

Please remember that the entire effect is proportional the total 
magnetic and ion densities, so the rotation is not going to be 90 
degrees or 180 degrees.  We will not always get RH OR LH, vertical OR 
horizontal.  If the right conditions exist a RH signal could actually 
turn into a linear signal.

Another factor to consider is the degree of rotation is proportional to 
the square of the wavelength. The effect is noticed at UHF frequencies, 
so for the many satellites whose uplink is UHF there is an effect but as 
we go to higher frequencies rotation effects become less a problem.  
Imagine the fun we had with mode A satellites in the beginning. All 10 
meter down link and 2 meter up link and the Sun was doing it's sunspot 
thing.

Well that's PHYSICS lesson for the day.  It's been a while that I could 
do that.

My advice for the day ---  get a switch!  You are going to need it. I 
always find, even now, that a switch in polarization at the antenna is 
needed to maintain a good QSO.

Have a good day, at home or where you have to be,

Jim Jipping, W8MRR
AMSAT # 5512