Long long, Lock-on time when in Portugal

RoystonB · Occasional Visitor Joined: Aug 16, 2006 Posts: 19

Hi All,
I just read a thread relating to the time it takes for the TT to lock on to satellite signals.
I have a 710 with all the latest updates that I can find from TT.

My problem is that although it only takes a minute or so to lock on when I’m in England, when I travel to Portugal it can take up to an hour. I usually switch it on as soon as I get the Car hire premises but it can take a long, long time to get a fix.

I’ve stopped downloading the QuickGPSfix in case that was the problem and I’ve purchased an extension aerial which I pop out the side window, in case of heated windscreen blockage.

I’m not sure what QuickGPSfix actually downloads, I’m in the London area. When QuickGPSfix is downloaded will my tt only search for those satellites visible from there, or is it a world wide sat. position fix?

Any thoughts on this problem would be most appreciated.

DennisN · Posted: Mon Apr 21, 2008 5:21 pm Post subject:

Presumably you fly there with the 710 switched off. My 710 took a few minutes to lock on when I went to Corfu last summer - the important thing is to leave it with a clear sky and not moving. I sat mine on a table on the verandah until it locked - don't know how long because I knew it wouldn't be instant and went to check if a beer in the fridge needed drinking before it went sour Twisted Evil

- by the time I'd done the bottle opener thing and tested the taste, I had a lock.
_________________
Dennis

If it tastes good - it's fattening.

Two of them are obesiting!!

Darren · Posted: Mon Apr 21, 2008 6:16 pm Post subject:

The delay when you initially switch on in Portugal is because you have moved thousands of miles since its last fix.

The satellites it expects to see are not there and so the device will download a full set of Ephemeris and Almanac data. Give it time to do this and it'll all run fine there after.

This is a good primer worthy of a quick read:

http://www.pocketgpsworld.com/howgpsworks.php
_________________
Darren Griffin

Andy_P · Posted: Tue Apr 22, 2008 12:46 pm Post subject:

Darren, just for interest's sake, I looked up your link to see what the difference was between the 'ephemeris' and the 'almanac' data.
Unfortunately...

Darren · Posted: Tue Apr 22, 2008 12:49 pm Post subject:

DennisN · Posted: Tue Apr 22, 2008 12:57 pm Post subject:

Well I looked and believed it all so much I nearly went out to buy three. Confused

_________________
Dennis

If it tastes good - it's fattening.

Two of them are obesiting!!

Darren · Posted: Tue Apr 22, 2008 1:29 pm Post subject:

I've re-written the entire section to clearly explain the differences between almanac and ephemeris data and tried to explain cold/warm starts and the issues that occur when you have moved hundreds of miles between position fixes. Thumbs Up

_________________
Darren Griffin

Andy_P · Posted: Tue Apr 22, 2008 2:28 pm Post subject:

Brill... all clear now! Thumbs Up

But... (there's always a "but" Laughing

)
From your description, it sounds like TomTom's "GPSQuickFix" downloads must be 'Almanac' data, whereas they always refer to it as 'Ephemeris' and the downloads even go in a folder called that.
Wikipaedia seems to agree with you... Are TT wrong again?

Darren · Posted: Tue Apr 22, 2008 2:31 pm Post subject:

IIRC QuickFix uses a calculation algorithm to calculate extended validity ephemeris data, I'll see if I can find a reference to it.
_________________
Darren Griffin

Darren · Posted: Tue Apr 22, 2008 6:46 pm Post subject:

From our resident tech guru:

Andy_P · Posted: Tue Apr 22, 2008 7:27 pm Post subject:

Curiosity satisfied , thanks!

(potters off to learn more about solar wind.....)

Calomax · Posted: Wed Apr 23, 2008 8:54 am Post subject:

RoystonB wrote

Darren · Posted: Wed Apr 23, 2008 9:02 am Post subject:

Calomax · Posted: Wed Apr 23, 2008 9:03 am Post subject:

Thanks Darren
_________________
TT Go Essential

	PocketGPS
	Web