It seems one of the latest GPS satellites is having signal distortion problems that can affect the accuracy of GPS units.
I wonder if that's why my house keeps drifting - oh wait, the mooring lines slipped.
To the best of my knowledge, that satellite's performance is still within spec but it has not been marked "in service" because its performance, without a "work around" is not up to par with the other satellites in its class. Bottomline - it is not affecting the performance of your GPS.
This bird has not even been put into service yet, so it has not had a chance to effect any GPS signals.
I have to disagree at one level. The sat has to be brought on line for testing or how else would they know if the signals were bad? When it is being tested, it does transmit and your unit WILL receive the distorted signal. We just don't know when it is being tested.
It can be tested and send signals without being set in service.
Interesting write up.
I was late because of the bad satellite. That's my story and I'm sticking to it.
As others have stated, it can be tested without actually being put into service and in use by your GPS. Yes, it is sending out signals, but the packets contain information within it that will let the GPS receiver know whether to use it or disregard it. Once the satellite is fully opertational, the packets will contain the "ok" to use data within and your GPS will of course use it to triangulate its position.
FWIW, the United States Naval Observatory has a web page that shows the current status of all the U.S. GPS satellites.
If the consumer level units have the code in their software to know if the data packet is valid? I know there are two levels of signals sent, one level being for mil-spec service and the other commercial grade service. Are the packets being transmitted in both services and does the commercial GPS units have the software to tell if a sat is in test mode only?
maybe we can launch him next Monday
If the consumer level units have the code in their software to know if the data packet is valid?
Since this is a basic function of the system, there is no reason why your unit wouldn't do this.
I'm sure if you plow through the references in the wiki page:
you'll find the exact answer.
most commercial/consumer units ignore birds in test mode. On some Trimble units using their proprietary protocols, you can force the receiver to use specific birds, including ones in test mode. Usually not a good idea.
There's a big difference between receivers and correlators -- a GPS receives (decodes and stores) almanac and ephemeris data on the birds (in the active constellation).
But for finding position, it uses correlation -- your GPS receiver already knows *exactly* the signal it is looking for. In essence, it slides that known signal back and forth (in time) in the correlation window trying to get the signal it's looking for to line up. If it does, and gets a good correlation, it looks at the time offset, and uses that offset along with the calculated position of the bird, to calculate the position of the GPS receiver.
This use of correlation is one of the reasons GPS receivers can pick up such weak signals -- for that portion of location determination, they know exactly what the signal is that they're looking for.
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