Actually, I would tend to suggest the majority of polarization shift is simply due to the always changing attitude of the spacecraft with respect to the user.
The fact that all TVRO Satellite dishes worked perfectly well when switching back and forth from horizontal to vertical polarization when changing channels and once the dish was initially aligned then those vertical and horizontal polarizations remained accurate across the entire sky and across the many dozens of satellites, then would suggest th contribution due to faraday rotation was small (at C band anyway)...
Yes, there is some faraday rotations at HF and at extremely low elevations, but I think for one using an ARROW antenna, all of the polarity issues are simply due to the instantaneous orientation of the satellite. Not the ionosphere...
But, just my humble opinion...
Bob WB4APR
-----Original Message----- From: AMSAT-BB [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob Sent: Tuesday, May 31, 2016 1:52 PM To: Doug Andrews Cc: AMSAT-BB Subject: Re: [amsat-bb] Polarization
"The antennas I see in the photos of satellites we work are whips. Is the polarization becoming "circularized" as it re-enters earth's atmosphere or something?"
Yep, that is exactly what is happening. It is called Faraday Rotation, and as the signal from the satellite passes through the ionosphere, all sorts of polarity changes can and do happen. A linear polarized satellite antenna (horizontal or vertical) can appear to be the opposite or somewhere in between. That's why folks rotate their Arrow or Elk antennas -- trying to match the polarity.
Using a circular polarized antenna helps a bunch -- it doesn't matter what the polarity of the linear satellite antenna happens to be at any moment in time.
But there is no free lunch -- Even a circular polarized antenna might need to be switched from Right Hand Circular Polarization (the default) to LHCP from time to time depending on what nasty thing the ionosphere is doing at any given moment. Changing the polarity switch might bring a S0 signal up to S5, a 30 dB improvement. I had that happen to me during a recent ARISS contact.
73, Bob, WB4SON
On Mon, May 30, 2016 at 8:25 PM, Doug Andrews dougg27@hotmail.com wrote:
I too have wondered about this. I have not had much trouble hitting SO-50 and some success on AO-85 with a 5 watt handheld and arrow antenna without turning it. Worth a try. DougKG7UNU
Sent from my Sprint Samsung Galaxy® Note 4.
-------- Original message -------- From: Ken Alexander k.alexander@rogers.com Date: 5/30/16 4:41 PM (GMT-08:00) To: amsat-bb@amsat.org Subject: [amsat-bb] Polarization
I clipped this from another message because I didn't want to drag the discussion off course. It's a question I've been wondering about since getting into this a few short weeks ago.
I've also read (but haven't tried yet) about the trick of rotating the antenna 90 degrees on transmit, once you've established the best receive orientation.
73 de Bill, KG5FQX
So far, with SO-20 I have rotated my Arrow antenna for best reception of the downlink and don't think I've had too much trouble being heard. At the same time I have wondered whether I should twist the antenna when transmitting to orient the 2m elements to give the same polarization as in receive. I don't know if this is a good idea or not, and frankly I have enough trouble remembering calls and grids, tracking the satellite, adjusting frequency and switching back to the correct VFO to worry about one more thing.
I've seen that some commercial OSCAR antennas use circular polarization. The antennas I see in the photos of satellites we work are whips. Is the polarization becoming "circularized" as it re-enters earth's atmosphere or something?
Comments and observations would be most welcome!
73,
Ken Alexander VE3HLS, FN03
Sent via AMSAT-BB@amsat.org. 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: http://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org. 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: http://www.amsat.org/mailman/listinfo/amsat-bb
_______________________________________________ Sent via AMSAT-BB@amsat.org. 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: http://www.amsat.org/mailman/listinfo/amsat-bb