Used GPS to compare my speedo yesterday...

You wouldn't want to have relied on GPS navigating around the freeway on the lower mainland of BC for the past couple year. A mega project rebuilding the whole freeway for about 20 miles. I think they rebuild and re designed every exchange in that project that is almost done now. I still think the maps have yet to be updates my whom ever does that, for this area.

 

The DOD have a system called selective availability, when activated then a commercial grade GPS will only be accurate to approx 100 metres. They used it originally, but it has been turned off since the mid/late 90's. Now too much stuff relies on it & they can't turn it off.

That said the USA are having trouble maintaining the satellites & the shuttle was supposed to return defective units to the ground. Now that can't happen, so they are likely to struggle in the future with US Budget cuts etc. That's why the Chinese crashed a missile into an old satellite, just to let them know that their smart weapons aren't & GPS can be jammed with some stuff from RS very simply !

It is NOT. A reliable system, the Royal Navy did a jamming test a couple of years ago here in the UK & wiped out a 200mile circle of reception from one ship. Deliveries of all sorts got screwed up that day, as they had told local media, but national didn't pick up on it !
On a seperate occasion a satellite died (space debris hit) and a boat approaching western Scotland suddenly had its GPS report it just off Norway approx 200mile error ! These are just a few I know of.

As a friend of mine who works on GPS receiver systems tells me, there is less energy reaching the earth from a GPS satellite, than if you had a candle burning on the moon (assuming it could burn there !) So very very weak signal, hence easily jammed.

Be careful out there.

 

Three words...

The Big Dig

 

Some people have way too much time on their hands!!!

 

That's what happens when you can't ride...