[amsat-bb] Polarization

[Bob]

"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 at 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 at rogers.com>
> Date: 5/30/16  4:41 PM  (GMT-08:00)
> To: amsat-bb at 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
>
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