Grey satellites on satellite view page

[proxima]

I have an eTrex Legend. It suits my needs perfectly, and works well. However, I have one question:

On the satellites view page, as well as the 'white' (out of sight) satellites, and 'black' (visible) ones, I get some 'grey' ones. Often these remain grey for quite a while, before finally turning black. What does the grey status mean?

[Tim Buxton]

Grey means that the unit knows that the satellite is there but is not currently using information from it. It's part of the 'handshaking' period, I suppose.
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Tim

[Skippy]

The satellites transmit data which contains information about the position of the satellite and other information. This data takes 30 seconds to transmit and it constantly repeats.

Your GPS can recognise the number of the satellite from the way the data is encoded (at this point the sat appears grey in your GPS display).

From "Cold", your GPS must receive a full 30 second data stream from start to finish before it can "lock" on to the satellite. If it gets interrupted during the 30 seconds then it has to go back to the start and wait for the stream to start over. This means the GPS will have to "see" the satellite for 30 to 60 seconds to get a lock.

If you are in open space when you get your first fix then it's worth waiting a minute or two for it to lock on to all the available sats before you move off. If you are moving then something could block the view and it will take longer to lock on. This is why some bars stay grey for quite a while - the GPS hasn't had an uninterrupted view of the sat for long enough.

Once it has the lock (black bars), it can lock on again almost instantly (ie a "Hot" fix) so it doesn't matter if it loses sight of the sats for a while.

If the GPS is switched off for a few hours, the data it downloaded becomes out of date and it does a cold start again.
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Gone fishing!

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