Synchronization of PDA clock with GPS clock

Buffy Beagle

Until yesterday I had assumed that, because accurate timing is fundamental to GPS, TTN would ensure that the Pocket PC's clock was kept synchronised with the real time as broadcast by the GPS satellites. I've looked up the NMEA sentence format and see that every positioning message received by the computer from the GPS unit incorporates the current UTC time.

However, I noticed yesterday that the ETA reported by TTN was 13 minutes too early and discovered that this was because our iPaq's clock was running 13 minutes slow.

Does anyone know if it is possible to arrange for the Pocket PC's clock to be synchronised automatically with the accurate time obtained from the GPS?

Hugh

Dave · Posted: Sun Oct 05, 2003 2:36 pm Post subject:

The Pocket PC time will not be set via the GPS atomic clocks. It's something I've thought should be done for quite some time.

I'm not too sure how accurate the clocks are, I know when I checked a while back I was getting some strange times back showing 1978, some showing 2007, this may have been down to receiving bad data at the time from these clocks. Any clocks that did show the correct date were offset on UTC and not BST, so grabbing the time is better done via your PC and making sure your PC syncs with an atomic clock over the internet.

Buffy Beagle · Posted: Sun Oct 05, 2003 6:02 pm Post subject:

Surely, the satellites must keep their clocks synchronized to the correct time in order that they can know where they are?

And therefore, surely, it should be a simple matter for TTN or some other program running on the PDA to use the time received from the GPS to update the PDA's clock, provided that it is told what time-zone to use?

Hugh

lbendlin · Posted: Mon Oct 06, 2003 6:53 pm Post subject:

Yes but as Dave states you should not always trust the stuff that the Sats are trying to tell you. Between them they already have some trouble to synchronize their atomic clocks properly (last week was especially bad) but then there's still the atmosphere distorting the signal that arrives at your GPS receiver. You can see that sometimes when your position jumps about even though you are not moving physically.. So it is well possible that the GPS time is not always stable. Maybe that's why some of the software vendors (like TomTom) are shying away from including this feature. I think they should leave it up to the user to decide if the Pocket PC clock should be set to the GPS time or not...
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Dave · Posted: Tue Oct 07, 2003 6:35 am Post subject:

I'm still waiting for a plug-in CF card that will receive atomic clock signals like some of the newer radio clocks you see on sale. That way you could just plug the card in, update your time correct then unplug it again. Or perhaps something that plugged into the sync port on the Pocket PC ?

cuk0724 · Posted: Thu Oct 09, 2003 8:13 pm Post subject:

GPS Dash is a small programe that will set your PDA clock from the received sat signal amonst other things.http://gpsdash.shows.it/

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