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Old 11-01-2006, 11:20 AM   #1
obk
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Default multiple sats and repeater simultaniously?

Stupid question probably (and yes, there are some stupid questions), but when I am listening to the sat reception, am I only connected to one satelite at a time, or can I be connected to the two in range... Also, if I am in repeater coverage area, am I actually using the repeater and the two sats? I know the aiming screen will show the amount of reception from sats and terrestrial together.
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Old 11-01-2006, 04:56 PM   #2
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I think the receivers have a way to lock in on whichever signal is the strongest at any given moment. For example, if Sirius 2 is the strongest satellite, your receiver will stay with it until the signal gets too low, at which point it will seek either another bird or a ground repeater. A good example of this would be when you go into a tunnel or under an overpass while driving. I'm just speculating here, of course.
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Old 11-01-2006, 06:10 PM   #3
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multiple sats and repeater simultaniously?
 
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Sirius units pick up all three signals together if possible. This can be done because they're all on different frequencies.

One statellite and the repeaters have a four second delay applied to them. The other satellite broadasts in real time.

The receiver has a buffer built in to it. This allows it to delay the real time satellite so that it matches the two other signals with the 4 second delay. These are digital signals.. There is no audio or any channels yet.

All three signals are fed into an integrator that combines them into one digital signal. The beauty here is that you can have up to two signal sources blocked, and you're still receiving a signal. If ALL the signal sources get blocked, you have up to four seconds of buffered signal from the real time satellite.

The integrator takes the three separate signals and converts them into one good signal. This is known as space and time diversity. It's needed for the rigors of mobile satellite reception where you're passing trees and buildings that can block any or all of the signals at one time or another. The idea here is to have as many signals coming in as possible.

To deliberately lock onto one source and ignore the other two would defeat the purpose of having time delays and signals coming from multiple sources.

There is on 'problem' with this.. That lies with the repeaters... The repeaters have a radiated power of thousands of watts. The satellites are up to 30,000 miles away and by the time the signal hits your antenna it's flea powered. The repeater signal can be up to a billion times stronger than the satellite signal..

If you're near the powerful repeater, it can swamp the satellite receiving portion of the radio and drown out the satellites. If you've ever get close to a repeater, you'll see the SAT signal disappear. This isn't desirable because you lose the advantage of the 4 second time diversity delay. It's technically impossible to get around this, so if you're close to a repeater and you get behind something that blocks the signal, then you get a dropout.

Edit.. I forgot to add a link.. You can read about it in more technical detail HERE

Last edited by jwt873; 11-01-2006 at 06:15 PM..
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Old 11-01-2006, 08:00 PM   #4
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Excellent explanation! Thanks!
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