Subject: Re: Link budgets for upcoming HEO/GEO sats
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
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@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 _______________________________________________ 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
Hi John,
On these ku band hd lnb's we're playing with for 10 GHz, you do have to be careful with the voltage fed to them as that is how they switch polarity remotely.
Typically, vertical is 12-14.5v and horizontal is 16-18v
Mike
On 4/11/2016 4:39 PM, John Toscano wrote:
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@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 _______________________________________________ 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
participants (3)
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Bob Freeman -
John Toscano -
Mike Seguin