Excellent Post, Jim and brings back some wonderful memories. 73, N0AN Hasan
On Wed, Mar 25, 2020 at 9:08 AM James Jipping via AMSAT-BB < [email protected]> wrote:
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 _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb