GPS - Selective Availability

[lezgar]

Last season my GPS gave a EPE (Estimated Position Error) of 3 feet. Today the GPS give a EPE of 98 feet.

Do you know if Selective Availability is on?


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[tome]

No, SA isn't on and nor will it be.

If necessary the US will locally jam the L1 frequency carrying the C/A code which is what we use (the military only use L1 for initial acquisition then switch to L2 Y code which is a different frequency and encrypted). The more modern mil GPS receivers don't use L1 at all. If you want to read more about it check out

<A target="_blank" HREF=http://www.rin.org.uk/SITE/UPLOAD/DOCUMENT/War&GPS.pdf>http://www.rin.org.uk/SITE/UPLOAD/DOCUMENT/War&GPS.pdf</A>

More likely to be poor geometry/blocked satellites. Where were you, and at what time?

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[snowleopard]

during the last disagreement with iraq the americans turned s/a off for the duration.

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[rob]

hi,
they never turned off!!
but they did do some thing

rob

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[BrendanS]

and as said before, it's been turned off permanently for a few years.

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[maxi]

Talking last week to someone within the Satellite industry, he stated that the geo-stationary satellites had been shifted in their orbits, to provide a consolidated band of cover over the middle east, giving accuracies there of some 13 cms, whilst further north and south accuracies were down to 90m or so.
Cruising the Red Sea this spring should provide a wonderful navigation opportunity.

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[pandroid]

They had to. They ran out of military sets and had to go and buy the boys some retail ones just like you and I have.

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[gjeffery]

I have not noticed any recent degredation and yesterday measured an averaged EPE of 17 feet.

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[qsiv]

My understanding was they turned it off in order to go and buy recreational (Garmin) GPS units to give to the grunts as they didnt have enough milspec kits to dish out. It's stayed off pretty much ever since, although it was only formal;ly turned off 3 or 4 years ago.

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