Terryl
Specialist Contributor
- My Satellite Setup
- OpenBox X5 on a 1 meter motorized dish.
And now a 10 foot "C" band dish.
Custom built PC
- My Location
- Deep in the Boonies in the central Sierra Nevada mountains of California.
The satellite down converted signals are in 1 block but with spacing between them, if you look at the transponders on one satellite you will see that they are spaced apart, all your LO in the LNB does is to mix with the amplified signals from the satellite at 10.5 to 12.2 GHz or 12.2 to 12.7 GHz in a frequency mixer, the LO (local Oscillator) is low side injection, what happens is the frequency's mix all up, this causes new frequency's to be created, some are +, lets say 11.5 GHz on the transponder, 9.750 GHz on the LO = 21.25 GHz, this is too high to send down the coax.
So with hi-pass and low-pass filtering the mixers output is restricted to the low band output, using the transponder of 11.5 GHz, minus the LO of 9.750 GHz, would give you a signal at 1.75 GHz to send down the coax to the receiver, this will work as the coax can handle this frequency.
But what happens is every transponder on that satellite of one polarity or the other gets down converted and sent down the coax, you can have as many as 20 signals coming down the coax, and they can be detected and demodulated with the right equipment.
Over here in the US the Dishnutwork satellite LNB's use band stacking, all one polarity is on one low band 950 to 1450 MHz, and the other polarity's are in the high band 1650 to 2150 MHz with a guard band of 200 MHz in between, with good equipment and a high gain antenna you can look at this signal and tell what satellite it is on, the FCC does this in some cases.
This is a view of the transponders before they hit the down converter in the LNB, it looks the same coming out of the mixer except they are at a higher level and in a different frequency band ("L" band) this is also called the IF signal.
So with hi-pass and low-pass filtering the mixers output is restricted to the low band output, using the transponder of 11.5 GHz, minus the LO of 9.750 GHz, would give you a signal at 1.75 GHz to send down the coax to the receiver, this will work as the coax can handle this frequency.
But what happens is every transponder on that satellite of one polarity or the other gets down converted and sent down the coax, you can have as many as 20 signals coming down the coax, and they can be detected and demodulated with the right equipment.
Over here in the US the Dishnutwork satellite LNB's use band stacking, all one polarity is on one low band 950 to 1450 MHz, and the other polarity's are in the high band 1650 to 2150 MHz with a guard band of 200 MHz in between, with good equipment and a high gain antenna you can look at this signal and tell what satellite it is on, the FCC does this in some cases.
This is a view of the transponders before they hit the down converter in the LNB, it looks the same coming out of the mixer except they are at a higher level and in a different frequency band ("L" band) this is also called the IF signal.
