Morning everyone!

Has anyone noticed their GPS devices (handheld, boat, car, computer and etc) acting strange lately?
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In my line of work GPS is second only to electricity on the "things needed" list to make a cell site work. Each cell site has two GPS devices and they are even calibrated for how many nanoseconds of delay the cable from the antenna to the device causes.

I began noticing my personal vehicle mounted GPS acting a little strange in that it was not keeping good time. Then I noticed it was also coming up about 300 meters off on fixes (like showing me at home when I was still 300 meters away), Keep in mind I used to judge distances in meters by eye as part of staying alive, so that eye is pretty well calibrated.

Next I noticed the computer based GPS in my work computer was also coming up funky. It was more like 150 meters, but it was at one time a government computer/GPS system I bought as a demo unit.

Later I ran into some surveyors using calibrated GPS equipment (the back pack style from trimble). The two fellows were arguing near one of my cell sites around 2500 meters in the back of a field near Kelly AFB. One was sure he knew where the benchmark they were looking for was, because he remembered placing it when that part of Kelly AFB was closed. The other said he was an old fool, because the GPS showed it was directly below their feet.

I had happened to see it inside the cell site compound, exactly 300 meters away from where they were standing! When I told them of this, they said their GPS must need calibration, because it has been acting "funny" for some time.

Later, I ran into several different Cell carrier technicians at a colocation facility, (Sea World to be precise). Each was complaining of issues with their GPS equipment in the shelters, and new antennas had not fixed the problem.

Finally, My son was having trouble last night making his deliveries, because his GPS seemed to be coming up wrong on occasion.

Is Uncle Sam playing with the system? I remember the PY codes were removed during the Clinton/Lewinsky administration, but this seems too uniform to be an accident.

The Garmin Nuvi 760 in my truck seems fine, but it cheats because it also uses the road as a reference. However, yesterday it showed me within a few meters of the waypoint I set a year ago which is close enough for my needs.

If there are issues I'll have a better idea when I use my Garmin 60CSx next weekend hiking down a local ravine. I'll track the ravine and then overlay the track onto the software map to get a ground truth.

In the last few months I have gotten "WEAK GPS SIGNAL" messages in canyons that have had good signals previously.

Four canyons, all runing north and south lose signals. Checking the history, I have many "TRACKS" running the full canyon with no lost legs. Now each canyon loses reception.

It could be Uncle Sam, then again it might not be. Spoofing the unencrypted 1.57542 GHz L1 PRN signals to generate a little local Selective Availability might be of course being performed by someone else. Jamming GPS is even easier. Just a scaled up version of one of these.

http://www.dealextreme.com/details.dx/sku.8758

http://news.bbc.co.uk/1/hi/england/cornwall/6719639.stm

Strange, maybe it's not just a coincidence. I've been very happy with my new Garmin but during the past several weeks I have experienced innacurate readings on several occasions, for the most part in terrain with a relatively good view of the sky where reception shouldn't be a problem. Several times the reading was off about 100 yards, which was really apparent - I was walking on top of a ridge or sitting by a lone building while according to the GPS, I was supposed to be a fair distance away.

One time it was a whole lot worse. I had the unit turned off and when I switched it on to check my position, I got a reading that was off like 200 miles, another state in fact! I was really baffled. To be fair, it happened in the middle of the bush, dense tree cover and all. But the signal did not improve at all after a few minutes. I switched the unit off and on and it worked, I got a good fix on my position right away.

Still, I thought it was very unusual. I've never seen it before so I don't know what to think.

a few summers ago my canoe buddys and i set our GPS units down next to each other to compare them and they were good to a couple feet..things are hot with the talban right now so i would assume to screw up their store bought units we are messing with the signals--

I've had two Garmins both got terrible signals... I stopped even trying to use a GPS for fun.

I have one still and after it failed to work AT ALL when I NEEDED it it's sat in a box somewhere

I was in Botswana, deep in the bush on September 11 2002. I could not hit a single waypoint that day and had to go back to map and compass. I reckon something was changed on that day!!!

Jeremy

300m off with the GPS units surveyors use? Wow, that's HUUUUUGE. I remember reading some specs on a Leica surveyors GPS unit. It said something like it is capable of accuracy to within 6 millimeters!!!

If anyone can give us an alternate satellite navigation system to GPS, it's...Google!

Here's a raw .dxf file generated from a GPS survey carried out by myself out on 11th September 2001. Accuracy was sub metre that day.