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CanarySlayer
Occasional Visitor
Joined: Feb 28, 2006
Posts: 4
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 Posted: Sat Sep 23, 2006 11:23 pm Post subject: GPS Satellite Grey bars |
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Hi
I am sure this question has a very simple answer, but forgive me for my lack of knowledge...but. I have just purchased a Holux GPSlim to replaced my original wired TomTom 3 receiver (very happy so far).
I am currently using TomTom 5.0 on an Ipaq 2210, but when i select the 'show GPS status' and the satellites are displayed, it picks up 10-12 satellites but there are only 9-10 that have blue moving 'signal strength' bars, the others display grey moving bars. I presume it is not using that satellite data for the grey ones, but those grey bars never turn blue if the other blue bars are lost.
I hope someone can make the murky water of GPS a little clearer to me.
Thanks very much |
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pendlemac
Lifetime Member
Joined: Aug 13, 2005
Posts: 72
Location: Lancs
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| Posted: Sun Sep 24, 2006 12:39 am Post subject: Re: GPS Satellite Grey bars |
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| CanarySlayer wrote: | I presume it is not using that satellite data for the grey ones, but those grey bars never turn blue if the other blue bars are lost.
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I was under the impression that it's more a case of 'it cannot use the data from the grey ones' rather than 'it chooses not to use the data from the grey ones'.
The receiver will use as many satellites as it can so in a perfect world you could get all twelve bars showing blue. :D |
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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: Sun Sep 24, 2006 2:25 am Post subject: Re: GPS Satellite Grey bars |
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| CanarySlayer wrote: | | it picks up 10-12 satellites but there are only 9-10 that have blue moving 'signal strength' bars, the others display grey moving bars. |
The receiver shows a grey bar for 30 to 60 seconds while it "aquires" the satellite. If something interrupts the view of the satellite then the timer resets to zero and it has to start again. Once it has been aquired (blue bar), it can reaquire the satellite almost instantly.
It often pays to switch to the satellite screen and wait a minute or two until you get all the available satellites aquired before you move off.
If you are moving while it's aquiring, then the view of the sats often gets blocked and the unit takes longer to aquire all the satellites. In some cases where you only have 4 or 5 sats, you can get big positioning errors.
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philpugh
Lifetime Member
Joined: Dec 28, 2005
Posts: 2003
Location: Antrobus, Cheshire
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| Posted: Fri Sep 29, 2006 5:37 pm Post subject: |
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| It requires to download the ephemeris data from the satellite in order to turn the bar from grey to blue I believe. Only then does the GPS unit have the precise information about the satellite required for it to be used in position calculations. |
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Border_Collie
Pocket GPS Verifier
Joined: Feb 01, 2006
Posts: 2543
Location: Rainham, Kent. England.
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| Posted: Fri Sep 29, 2006 10:44 pm Post subject: |
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To put it simply, after doing my brain in reading up on all this.
The satellites send information about all other sats. therefore you will get info of the 12 in view. If a satellite is low down on the horizon you won't necessarily receive the signal from it. If the satellite happens to be 'rising' then you'll find there will come a time when your 'signal strength' bar turns blue. If they are blue and turn to grey, the satellite has moved down towards the horizon.
You only really need 4 satellites to give a 3D fix of where you are so any excess data will be ignored.
When you start TT, go into the GPS screen and you'll see the satellites towards the centre of the 'compass' are blue and the nearest to centre will be the furthest left blue bar. The ones on the out edge are low down on the horizon and will probably be grey as will the corresponding bar.
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