Spot Beams

[ejjames]

I'm interested in knowing more about spot beams and how they work. It seems like amazing technology we just sort of take for granted.

[veryoldschool]

I'm not sure how amazing they are. They're simply a smaller focused antenna beam. Smaller area = stronger power density for the same power out. What makes them "most useful" is, since they're localized to one area, it means the same frequency can be used in another part of the country, without crosstalk.

[carl6]

In a way, you can think of spot beams much like a local over the air television station. There are a lot of channel 5's (or 2, or 7, or whatever) in the country, but none of them are in adjacent cities. That same frequency is being re-utilized many times over. In the case of the tv stations, the transmitters are widely separated. In the case of spot beams, the transmitters are beside each other, but have a very tightly focused beam that is aimed at parts of the country that are widely separated.

[ejjames]

Thanks for the info/

[HoTat2]

It is also important to keep in mind the uplink side of the matter where spotbeam capability is made possible by having unlinks to the satellites spotbeamed as well. That is the satellites are designed to receive from only certain locations on the earth.

Thereby allowing multiple strategically placed ground stations to reuse the same entire 500 MHz uplink bandwidth to communicate with separate transponder groups on the satellite (for example six ground stations for the Ka band birds DIRECTV10/11). With one or possibly two of the stations assigned to uplinking CONUS beam transponders for national programming and possibly spotbeam transponder groups for LiLs. And the others uplinking solely to spotbeam transponder groups for LiL markets.

[veryoldschool]

It is also important to keep in mind the uplink side of the matter where spotbeam capability is made possible by having unlinks to the satellites spotbeamed as well. That is the satellites are designed to receive from only certain locations on the earth.

Thereby allowing multiple strategically placed ground stations to reuse the same entire 500 MHz uplink bandwidth to communicate with separate transponder groups on the satellite (for example six ground stations for the Ka band birds DIRECTV10/11). With one or possibly two of the stations assigned to uplinking CONUS beam transponders for national programming and possibly spotbeam transponder groups for LiLs. And the others uplinking solely to spotbeam transponder groups for LiL markets.
I'm not sure what this has to do with "spot beams", since this is on the uplink side. Given that the receive antennas are pointed to different ground locations, yes they can "re-use" the same frequencies and the switching inside the SAT will determine what part of the uplink goes where on the downlink.

[evan_s]

On the Ku side of things multiple uplink facilities are required to use spot beams effectively because you only have an equal amount of uplink bandwidth to downlink bandwidth. You need to have some way to get the signal uplinked before it can be downlinked on a spotbeam. On the Ka side of things they actually have twice as much uplink bandwidth as downlink bandwidth so could do some spots with out having multiple uplink facilities but it doesn't ultimately end up being enough so they still use multiple uplink facilities.

[Mertzen]

just some cool spot beam maps:

http://www.scottandmichelle.net/scott/spots1.png

http://www.wildblue.cc/wb1.jpg