Strange GPS readings near Grayling?

[kroppe]

We drove from St. Ignace to Ann Arbor today, and I was getting non-sensical readings from my Magellan Sport Trak Pro from Indian River down to Roscommon along I-75. North of there, and south of there, the readings were fine.

I was getting things like 975 mph, heading of north when I was heading south. Completely off kilter.

Has anyone else had this problem? This sounds crazy, but is it something to do with the fact that the Army base is in Grayling and the signals get scrambled? I just thought it was strange.

Of course the GPS unit could be acting up, but it was acting fine earlier that day, and as I mentioned once we got south of Roscommon everything was OK again.

While I was getting the strange readings, I checked what I think is the "signal strength" screen and I didn't have the usual number of 4 or so strong satellite signals. Why would this be?

[Mike]

Maybe because of the military base?

Mike

[wmduckman]

There is signal jamming technology for G.P.S. guided bombs. I'm sure they are jamming incase of any incomming.;)

[SnowSledHead]

Probably just a couple satelites acting up. You didn't see any black helo's w/ U.N. markings did you?! Ha!:eek:

[Huntress]

kroppe,

I think that being near the Army base had a lot to do with your GPS acting up. The Government does scrammble the signals to help with security issues. Have you noticed any other times your GPS has not worked correctly? I would recommend calling the manufacturer of your GPS unit if you continue to have concerns.

Best Regards,

Huntress

[stoney]

kroppe,
I have the same model as you and have not notice anything like that. I have only had it for a couple of months and have not been up 75 yet this year. Next time I get up that way I wil try to remember to have it on...

Stoney

[SnowSledHead]

Quote "While I was getting the strange readings, I checked what I think is the "signal strength" screen and I didn't have the usual number of 4 or so strong satellite signals. Why would this be?"


All it was was just a couple satellites that were off line for periodic adjustment. Plus you were in hill country and the antenna is on the unit and not an external on the roof, right? Plus, most windshields have UV blocking filters in them and it blocks RF signals. Ever see a Ford coming down the hyway at you and see the rainbow on it's windshield?
It had Nothing to do w/ the Camp at Grayling. Happens all the time. If you used your GPS 6-10 hours a day you would see it often.:D

[jduck]

Being in the National Guard I spend a weekend a month up in grayling, and usally have the gps running, and it happens every so often. But I have to agree its not because of the military base there... Nothing anyone would want to bomb anyway :D

[wackoangler]

I am a surveyor and use "real GPS" often. Lots of things happen that can screw up your coordinates, most likely it had nothing to do with your unit, and if you use it enough, you will probably see it happen again.

[Hunt4Ever]

A combination of lots of things probably. Even time of day can impact accuracy.

I fly airplanes for a living and we run "Predictive RAIM" tests on long range routes (anything over 1,000 miles or so ) to see if we will have adequate satelite coverage to provide us with minimum navigational requirements. Sometimes we don't get it. Once we didn't get it 4 miles from Ann Arbor. That one was just the time of day and the position of the satelites.

[dogjaw]

A friend of mine can't use his gps in his Toyota Tundra pickup. The electronics in the truck screw it up. He has a digital compass in the overhead console. Maybe that's it.

[SARDog]

He might need an external antenna to run it in his toyota.

[dogjaw]

Aaaaaaaaaaaaaaaaaaaaaaah, I'll pass that along to him. Thanks.

[PaulD]

I Am a Sergeant in the Michigan Army National Guard and we use our personal GPS all the time in the field @ Grayling. I have never encountered any problems. Maybe it was just bad signals? :confused: Paul

[MSUICEMAN]

Although most likely this wasn't the reasoning, sometimes (and i do mean sometimes), around some installations, home GPS units will not get true readings as a safety measure. The government controls the accuracy of the GPS signals, and can (and will) use their discretion as to accuracy.

Not saying that this was the problem, but it could have been. I've heard several other accounts of bad readings near Grayling, and my buddy's was giving some weird readings near Fort Hood, TX when we were there also.

Steve

[wackoangler]

The thing is that if it was the feds doing something to the signals, you would know it everywhere, not just in one area, the sattelites are a long ways up there, and the radio waves that your reciever gets from them can be picked up for thousands of miles.

[twohats]

There has been some very strong solar activity this week that has been causeing problems with some sat. comunications. Space.com posts info when ever there is strong solar activity that could effect comunications.

[ih772]

:yeahthat: ...

[Rondevous]

I was getting things like 975 mph, heading of north when I was heading south.



You were driving the the "TOP SECRET" new FORD I bet :)

Rumor has it, The NEW FORD production will start about three days before we run out of fossil fuel :)

[MSUICEMAN]

the new ford concord.....

[kbkrause]

The thing is that if it was the feds doing something to the signals, you would know it everywhere, not just in one area, the sattelites are a long ways up there, and the radio waves that your reciever gets from them can be picked up for thousands of miles.

You wouldnt have to mess with the signals at the satelite, you could just scramble the signals with some ground based signal

[umas911]

Well if the millitary use gps why would they scramble there own signal?

[ih772]

All the information you could ever want about GPS and how it works is on this page. Somewhere it explains how solar flares and other phenomenon disrupt the signals from the GPS satellites and give erroneous readings.

http://gpsinformation.net/

[sfw1960]

BJ probably passed close to a RADAR transmitter near the base & got EMI/RFI.
(Electro Magnetic Interference/radio frequency interference)

G00GLE (http://www.google.com/custom?q=interference&sa=Google+Search&sitesearch=gpsinformation.net)

[TomW]

Although most likely this wasn't the reasoning, sometimes (and i do mean sometimes), around some installations, home GPS units will not get true readings as a safety measure. The government controls the accuracy of the GPS signals, and can (and will) use their discretion as to accuracy.

Not saying that this was the problem, but it could have been. I've heard several other accounts of bad readings near Grayling, and my buddy's was giving some weird readings near Fort Hood, TX when we were there also.

Steve

The accuracy is controled by the government, but it's completely based on the satalite. The way these units work is via very acurate timing singnals encoded into the signal beamed to earth by the bird. The receiving units can be jammed, but probably wouldn't function at all in the area. I have seen what you have discribed happen frequently in all sorts of areas mostly in the woods or in urban areas with lots of tall buildings when moving relatively fast on the ground. (bike, car or running). It usually occurs when some of the satalites signals are momentarilty lost or when a bird goes below the horizon and another hasn't been acquired. I was on a train once and the GPS told me I momentarily jumped to Japan and back when I looked at the recorded track on my computer!

Tom W