What's a Transponder?

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ride525

SatelliteGuys Pro
Original poster
Sep 7, 2003
443
0
SF Bay Area, California
I have a Dish 500 system. When I go and check the Dish signal strength, I see various transponder numbers on the screen, which I can change.

What is a transponder? Where are the different numbered transponders located?

Thanks,

Jeff
 
I'm not sure if this is the right way of putting it but each Sat. has a number of transponders and each transponder holds a number of channels. So a transponder is a group of channels.
 
My rough uneducated understanding was a transponder is the mechanical object on the satellite beaming channels down.
 
ride525 said:
I have a Dish 500 system. When I go and check the Dish signal strength, I see various transponder numbers on the screen, which I can change.

What is a transponder? Where are the different numbered transponders located?
Each DBS satellite location has a section of frequency set aside for broadcast. That bandwidth is divided into 32 frequency chunks, and each is assigned to a DBS provider.

The satellites that DBS providers launch have "transponders", which are simply put transmitters - each of which broadcast on one of those 32 frequencies. What you are seeing on your signal strength screen are the transponders (on frequencies) licensed to E*. On 119º you can scan through 1-21, on 110º you can scan through 1-27, 29 and 31. On 148º you can scan through all 32 and on 61.5º you can scan through even transponders 2 through 22, as well as 25-32. These represent the frequencies E* has permission to use.

Each transponder signal carries a QPSK modulated* MPEG-2 encoded signal that mixes many video and audio signals together. For you to tune a channel on your receiver, it must know what transponder to tune to, then what digital streams within that signal to use to create the channel you have chosen. Each signal on a transponder carries up to 12 video and audio signals. Through creative numbering, it appears that some have more than 12 channels, but they don't!

You will notice while looking that some of these transponders read 0 signal, and some of them read as spotbeams. On 119º, E* has taken transponder frequencies for transponders 1,3,5,7, and 9 and instead of using a large transmitter that would reach the entire nation, they have divided the footprint up so that frequency can be reused. Depending on where in the country you are, you receive a different set of spotbeams than people in other parts of the country. There are five spotbeam transponders possible on each freqency in E*'s system - almost all channels on spotbeams are local broadcasters. (On 110º the spotbeams are 2,4,6,8, and 10.)

Most of this is more than you asked, but I hope it answered the basic question. Once you get into this it seems that a transponder becomes a transponder - no definition possible. :)

JL

*Some of the transponders use 8PSK encoding instead of QPSK. Only newer receivers can decode 8PSK (including HD receivers, older ones will have a 8PSK module if they can receive these streams). 8PSK is currently used only for HD programming, and can run at a higher symbol/bit rate than QPSK. More bits means a better picture. If E* converts their primary feeds over to 8PSK they will need to replace most every receiver in the market. Look at 110 West, Transponder 13. If you have signal strength 0 then you have a QPSK receiver (or a bad installation). If your signal strength is normal, you have an 8PSK receiver (HD or 311/322/522 IIRC).
 
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