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philpugh Lifetime Member
Joined: Dec 28, 2005 Posts: 2003 Location: Antrobus, Cheshire
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Posted: Tue Jul 04, 2006 6:33 pm Post subject: SA - is it being turned off and on? |
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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 |
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lbendlin Pocket GPS Staff
Joined: 02/11/2002 22:41:59 Posts: 11878 Location: Massachusetts, USA
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Posted: Tue Jul 04, 2006 11:17 pm Post subject: |
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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. _________________ Lutz
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philpugh Lifetime Member
Joined: Dec 28, 2005 Posts: 2003 Location: Antrobus, Cheshire
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Posted: Wed Jul 05, 2006 1:45 pm Post subject: |
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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 |
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fwor Occasional Visitor
Joined: Dec 01, 2005 Posts: 39
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Posted: Sun Jul 09, 2006 12:17 am Post subject: |
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lbendlin wrote: | No they are not. Clinton had it switched off for good. |
Lutz - are you sure about that? My (typically bad) memory had me thinking that Clinton agreed to have it turned off, but the US military reserved (and still have) the right to turn SA back on anywhere in the world at any time 'if they needed to'. I thought that was one of the justifications for the European Galileo system? |
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lbendlin Pocket GPS Staff
Joined: 02/11/2002 22:41:59 Posts: 11878 Location: Massachusetts, USA
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Posted: Sun Jul 09, 2006 12:45 am Post subject: |
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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... _________________ Lutz
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Foghat Occasional Visitor
Joined: Jun 21, 2006 Posts: 8
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Posted: Wed Jul 19, 2006 2:30 am Post subject: |
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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. |
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Arimus Regular Visitor
Joined: 25/11/2002 13:13:12 Posts: 117 Location: Wales, United Kingdom
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Posted: Thu Jul 20, 2006 10:41 pm Post subject: |
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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. |
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Skippy Pocket GPS Verifier
Joined: 24/06/2003 00:22:12 Posts: 2946 Location: Escaped to the Antipodies! 36.83°S 174.75°E
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Posted: Fri Jul 21, 2006 12:08 am Post subject: |
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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. _________________ Gone fishing! |
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Quantum Frequent Visitor
Joined: 16/02/2003 03:21:58 Posts: 285 Location: Seattle, Ecotopia
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Posted: Fri Aug 04, 2006 3:04 pm Post subject: |
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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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