SA - is it being turned off and on?

philpugh

I've noticed on my last walking / cycling trips (over the last couple of months) that my GPS log (taken every 10 secs) seems to be dead on the road / footpath for all but a couple of random points which seem to be 20-30metres out. Now these have been 3-4hour trips and the last one (a walk) was undertaken in a treeless environment (Kinder Scout - Derbyshire) so I don't believe they are environmentaly produced.

I was wondering if the US military are 'playing' with SA at present?

Phil

lbendlin · Posted: Tue Jul 04, 2006 11:17 pm Post subject:

No they are not. Clinton had it switched off for good.

Don't forget that GPS is stochastic. You will never have absolute precision. There may be a ionised cloud overhead etc. Or maybe a reservoir of quicksilver underground. Don't try to put tooo much meaning into it.
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philpugh · Posted: Wed Jul 05, 2006 1:45 pm Post subject:

Thanks for that - I realise that you can't put any reliance on position - but I haven't notice such obvious (one off) changes in my track logs since the days of SA.

Phil

fwor · Occasional Visitor Joined: Dec 01, 2005 Posts: 39

lbendlin · Posted: Sun Jul 09, 2006 12:45 am Post subject:

You are right, since the system is operated by the US Navy they can do with it what they want. Currently it is however highly unlikely that they " play with it" in the UK area.

In addition SA has been made mostly obsolete by the introduction of earth based DGPS (along the coastlines etc). So you could find ways around SA if they decide to switch it on again.

Other than that yes, Galileo is supposed to remove the dependency on GPS, in order to create a dependency on, uhm, Galileo...
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Foghat · Occasional Visitor Joined: Jun 21, 2006 Posts: 8

Rumour at Trimble is that the US is playing with things at present due to the North Korean missile testing that's been going on recently.
GPS surveyors are noticing various anomalies that fit with this too.

Arimus · Posted: Thu Jul 20, 2006 10:41 pm Post subject:

Nope, no issues SA. I've got access to both keyed and unkeyed receivers with SAAS modules and not noticed over the last month anything odd.

Skippy · Posted: Fri Jul 21, 2006 12:08 am Post subject:

What you are seeing is just the random jitter in the GPS positioning.

You would hear about it pretty damned quick if the Americans started messing about with the GPS system - there would be a hell of an uproar.
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Quantum · Posted: Fri Aug 04, 2006 3:04 pm Post subject:

Phil, chances are that what you are seeing is due to multipath interference. SiRF3 is particularly vulnerable to this.

When I used to go downtown with my Holux236, it would skate me all around, turn me on my head, and have me skidding out into the grass. Far less of an issue now, with the new Nemerix chipset pods. (iTrek M5)

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