Sport Pilot Talk

ibgarrett · Joined: 04 Dec 2008 Posts: 147 Location: Westminster, CO

This one has me baffled. http://www.aopa.org/advocacy/articles/2011/110520gps_testing_in_new_mexico_prompts_advisory.html

How does a GPS system, which triangulates a given position using three satellites, just "stop working" in a given area?

Certainly I'm making the assumption that the planes are flying, so clear vision of the sky, so it's not a visibility issue.

Could it be a radio frequency jamming things? This is New Mexico after all, home of the alien landing (Roswell), so it could be anything...

I'm seeking smarter minds than my meager brain to sort this part out...

roger lee · Posted: Fri May 20, 2011 2:52 pm Post subject: GPS

Hi Brian,

This is not that uncommon and there are a couple of things that can cause it. First, if you have a Garmin they had some issues with
antennas. I had that problem and they sent me a new antenna and the problem was fixed. Second the auto locate function sometimes needs resetting. Third make sure your GPS has all the latest updates from that company.

Here is how to do 2 Garmin (296, 396,496) GPS resets.

If you have a slow or a gps that takes 10 minutes to pick up a satellite here is an easy reset.
This one is how to reset the "Auto Locate" function so the gps will hopefully do a quicker job at finding itself.

Press and hold the "Out" function and then press and hold the "Power" button until the "I Agree" message comes up. This only resets the satellite locating function and you will not loose any data.

This next one is a hard reset and will dump any saved data like way points or routes, ect... This one is used if nothing else works.

Press and hold the "Quit" button, the "Out" button and then the "Power" button. Hold all three down for 15 seconds. This is like re-booting your computer.

ibgarrett · Joined: 04 Dec 2008 Posts: 147 Location: Westminster, CO

But wouldn't antenna issues, software issues (auto locate for example) or updates then present the same problems throughout the country rather than in one specific area? I seem to remember there have been other postings for this type of issue in NM before.

I just find it odd to pre-announce an issue and not even related it to a particular GPS type of system. From the AOPA announcement it doesn't say a specific GPS, but rather "potentially unreliable GPS signals"

I can totally buy if an antenna wasn't installed/mounted correctly, but then why not specify that as the issue than the way they did?

It just seems to be a little more involved than what's being described...

Jon V · Joined: 21 Apr 2011 Posts: 156 Location: Dallas...

They are probably doing localized jamming/spoofing of the clock signals or ephemera...or something that will confuse receivers anyway.

GPS works by referencing the receiver to transmitters which have known positions. If you transmit a signal which looks valid but is coming from the wrong position(s) or contains incorrect information, the receiver will use the garbage signal(s) to give you a garbage position.

zaitcev · Joined: 05 Jan 2010 Posts: 258 Location: Albuquerque, NM

ibgarrett wrote: This one has me baffled. http://www.aopa.org/advocacy/articles/2011/110520gps_testing_in_new_mexico_prompts_advisory.html
It's just one of those experimental Light Squared towers. I am suriprised that you haven't heard about it, forums and media are overflowing with discussion. This is a typical example:
http://www.pilotsofamerica.com/forum/showthread.php?t=41909

zaitcev · Joined: 05 Jan 2010 Posts: 258 Location: Albuquerque, NM

Jon V wrote: They are probably doing localized jamming/spoofing of the clock signals or ephemera...or something that will confuse receivers anyway.
Not even close. It's just unrelated transmissions in the adjacent band that GPS receivers pick up because it's impossible to create an ideal band filter.

Jon V · Joined: 21 Apr 2011 Posts: 156 Location: Dallas...

Now that you mention it I remember reading about LightSquared/LTE GPS interference...but that was months ago and based on simulated tests, not real world towers.

I take it they are testing with actual equipment now?

zaitcev · Joined: 05 Jan 2010 Posts: 258 Location: Albuquerque, NM

L4 are testing and in fact they have tested in NM, but at appears that the next test is in the area of Las Vegas, NV. Therefore, I jumped to conclusions improperly. Russ Niles of AVweb says:
Quote: It's not immediately clear if the advisory is related to LightSquared's ongoing program to test for interference resulting from its 4G broadband transmitters.

ibgarrett · Joined: 04 Dec 2008 Posts: 147 Location: Westminster, CO

I'm going with alien transmissions... at least it sounds good to conspiracy theorists... :)