Has anybody noticed the GPS signal is scrambled again? I was trying to get a rough layout on some property lines in the mountains and it was wandering all over the place. Is it just my Delorme PN-20 getting old or what?
GPS Scrambled? (1 Viewer)
- Thread starter SteveLCetc
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
were you near a military installation? they scramble gps signals close to bases sometimes.
- Joined
- Sep 17, 2003
- Threads
- 65
- Messages
- 4,456
- Location
- Sunnyvale, CA
- Website
- www.george4wd.taskled.com
Did you check to see how many satellites you had locked and what the geometry was. Most GPS units can report the overall position fix 'quality' - if you were surrounded by mountain peaks etc you may have had limited satellite reception leading to a bad GPS solution/fix.
There is no magic with a GPS 'fix', you need several satellites with good geometric separation to enable good triangulation. Worst case would be 3 or 4 satellites in view but all in line or in one quadrant of the sky.
I REALLY doubt that the DOD has re-implemented SA, especially given the ever increasing reliance of GPS data.
cheers,
george.
There is no magic with a GPS 'fix', you need several satellites with good geometric separation to enable good triangulation. Worst case would be 3 or 4 satellites in view but all in line or in one quadrant of the sky.
I REALLY doubt that the DOD has re-implemented SA, especially given the ever increasing reliance of GPS data.
cheers,
george.
Same problem in NorCal yesterday, was about 50' off...weird.
Try this and see if the date/location may be related:
https://www "dot" notams.jcs.mil/dinsQueryWeb/displayGPSWAASNotamAction.do
The gov'mt periodically conducts intentional degradation or outright denial of the signals; these NOTAMs are designed to warn pilots before they plan a flight relying upon GPS in those areas.
https://www "dot" notams.jcs.mil/dinsQueryWeb/displayGPSWAASNotamAction.do
The gov'mt periodically conducts intentional degradation or outright denial of the signals; these NOTAMs are designed to warn pilots before they plan a flight relying upon GPS in those areas.
- Thread starter
- #8
Using a Delorme Earthmate PN-20 I got an error ring that was significantly less in diameter than the track I got when I just set it stationary. I had several satellites green. I was not near a military installation.
psfpilot, your link comes up with an invalid security certificate.
psfpilot, your link comes up with an invalid security certificate.
- Thread starter
- #9
This happened last weekend, +/- one day of Sept 11th, less than 20 miles from Los Alamos National Lab. That must have applied SA for that weekend there. Hopefully they have turned it off now... I'll find out tomorrow.
Checking against my two laptop systems yesterday at home the error was reduced and comparable to those other units, but still above normal.
Thanks for the responses!
Checking against my two laptop systems yesterday at home the error was reduced and comparable to those other units, but still above normal.
Thanks for the responses!
The secure DoD sites' encryption certs are not recognized by IE and Firefox's built-in list of certificate publishers; you'll have to click the buttons to allow the browser to go there after the cautionary message pops up. I forgot about that, as I have mine set to permanently accept that encryption certificate and no longer get the warning every time.
you probably just had crappy PDOP. you can look up the PDOP forecast for the day & area you will be going. It will tell you times of the day that you will get the best "reception"
Southeast Overland
Get lost! Go explore!
More than likely you had poor satellite geometry / alignment in the sky which = poor PDOP (Dilution of precision (GPS) - Wikipedia, the free encyclopedia) which = poor collected data accuracy. Higher end GPS units will effectively 'cut off' data collection when accuracy is too poor.
rusty_tlc
Dain Bramaged Member
Really? I wonder how they could localize that. If they modify the signal from the GPS sats I would think it would affect the hemisphere.
- Thread starter
- #14
Actually I have seen that in action. Flying from the San Francisco Bay area to Albuquerque one gets close to the Nevada Test Site. Flying south of it and turning to fly over Vegas I have, on more than one occasion, seen the track take off to the northwest - this despite that according to the topo below and shadows from the sun we were still on track for our destination...
You are correct though in that I agree that the algorithm is quite complex. It is a local phenomenon though.
You are correct though in that I agree that the algorithm is quite complex. It is a local phenomenon though.
rusty_tlc
Dain Bramaged Member
Maybe a low power interference signal on the same frequency?