[amsat-bb] Subject: Re: Link budgets for upcoming HEO/GEO sats

[John Toscano]

I don't know that the polarization has been fully decided at this point.
But one discussion I heard was talking about designing a dual-band feed
horn so a single dish would suffice for both uplink and downlink. They were
saying that one band would be vertically polarized, and the other would be
horizontally polarized, to help get as much isolation between the two bands
as possible. So, we are looking at linear polarization, or more precisely,
two different linear polarizations at 90 degrees from one another.

The FTA Satellite TV LNB that we are experimenting with for the 10 GHz
downlink typically fit into a circular holder on the offset feed arm, and
you can simply rotate the whole feedhorn in the holder to vertical,
horizontal, or anywhere in between, and then clamp it down. Folks with two
dishes to isolate the uplink from the downlink will simply have to use a
feedhorn with the correct (TBD) polarization on the 5 GHz uplink.
Typically, a homebrewed feedhorn often uses a SMA Coaxial to Waveguide
adapter, and the polarization is determined by whether the SMA connector
enters the mouth of the waveguide from the top, bottom, or side. So,
getting the right polarization is mostly a matter of knowing which band
will be polarized which way.

John

On Mon, Apr 11, 2016 at 9:56 AM, Bob Freeman <uwaveguy at gmail.com> wrote:

> Hello,
>
> Have been monitoring the link budget discussion and have questions about
> polarization.  Unlike the 2m and 70cm LEOs, I assume the spacecraft will be
> stabilized with a fixed polarization and not susceptible to Faraday
> rotation.  What polarization is planned for the satellite for up and down
> link and do we need to start designing polarizers for the link?
>
> Keep up the great work!
>
> Regards,
> Bob
> KI4SBL
> http://ki4sbl.dodropin.org/CNCTRK
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