[TruthInThoughtWordAndDeed]

Then please explain the bit about the signal disappearing as you drive south into Mexico.

[discostu]

When it comes to signal range a satellite is functionally a REALLY tall tower, nothing terribly magical about it, and still subject to being on the other wrong side of the horizon and unreachable. If the satellites your GPS is talking to are exclusively over America you will still wind up over the horizon eventually.

[Magnum44]

The signal is not disappearing. Its world wide, over land, over sea, in the low Earth orbit range and used out even at Geosynchronous altitude today.

What GPS does not do: GPS does not penetrate solid walls or structures well. It does not penetrate Earth. So signal strength becomes inadequate when you are in steep canyons, surrounded by tall buildings like in big city streets, or indoors or caves. Or if someone has a transmitter that is blasting noise on the carrier frequency.

If you have experienced this in Mexico and it was actual jamming, the only thing I could guess at was that south of the border, where the FCC cant enforce its rules, some cartel types could conceivably use jammers to frustrate law enforcement. But I doubt that's the case.

[semimojo]

I have no knowledge of or explanation for that. I was only responding to your comment that the effect couldn't be regional if GPS was satellite based.

[DBrow]

“Then please explain the bit about the signal disappearing as you drive south into Mexico.”

I’ve used GPS in Mexico, Bolivia, and Paraguay. As long as my antenna can “see” three sats I’m OK.

The signal can be obscured by clouds and rain but the sig definitely comes from the GPS constellation.

DGPS is a system that uses ground-based transmitters to enhance the 17 meter accuracy of GPS, DGPS is definitely ground-based, but sat GPS coverage is pretty much global except for parts of Antarctica where the birds are too close to the horizon to get three at a time.

http://www.gpsinformation.org/dale/dgps.htm