Waiting for valid GPS ... and waiting ... and waiting!

Trevor1234 · Posted: Wed Jun 17, 2009 10:47 pm Post subject:

Hi Folks
There is one thing that I learned from this Forum yonks ago and that was to keep away from ‘Home’ when ever possible. As far as I am concerned its for downloading maps and nothing else. I get a fix very quickly without any help from ‘Home’ and when I think back to the days when I first had a PDA running Tomtom 3 I marvel at the current fix time.
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Tomtom Go 720.
Navcore 9.510
Central and Western Europe v855.2884
GPS World Traffic cameras
Home 2.7
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MrT · Posted: Thu Jun 18, 2009 7:35 am Post subject:

On the X40 range it appears that it will bypass Home and download the QuickGPS fix itself via its inbuilt mobile and there appears to be no settings to control this. I thought it was a manual update function in the unit but it seemed to have done it on its own when I was recently away on holiday and had no access to Home.
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Drivelux

layingback · Regular Visitor Joined: Feb 12, 2009 Posts: 124

quickfix - or equivalent - should help you get a quicker fix in either (or both) of the following situations:

- you've moved the unit a big distance with it powered off, so that it can no longer find the satellites where it is going to initially look for them, which is where it thought it left them (basic rule of thumb is 100 miles);
- unit has been powered off (asleep) so long that the satellites have moved (can't remember the period, but a few days won't be a problem).

Otherwise it will just look for the satellites where it last saw them, and if it can find at least 2 within the range it's looking at it'll be away.

Obviously the above assumes a 360 degree clear view of the horizon, and performance degrades as that drops, but not as badly as one might initially assume, 'cos way more than the 3 needed for a fix are visible horizon to horizon.
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DennisN · Posted: Thu Jun 18, 2009 7:32 pm Post subject:

dhn · Posted: Thu Jun 18, 2009 8:36 pm Post subject:

Yeah, but if your fridge was on Crete ...... Razz

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David

AndyVaughan · Posted: Thu Jun 18, 2009 8:41 pm Post subject:

..... or back at home in your kitchen ...........

DennisN · Posted: Thu Jun 18, 2009 9:14 pm Post subject:

I can't win can I? I make my first serious post this month and promptly some bloke from out west and some bloke from up north both jump on it and give it a ridiculing.

My fridge is right here behind the swivel chair in my computer room.
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Dennis

If it tastes good - it's fattening.

Two of them are obesiting!!

Andy_P · Posted: Thu Jun 18, 2009 9:58 pm Post subject:

There's a couple of widely-held misconceptions rearing their heads again here....

Firstly, no sat-nav can "find the satellites where it is going to initially look for them" as it only has a single not-very-directional aerial and is a passive receiver.
It actually just receives data from the various satellites saying where THEY thought they were at a particular time (the ephemeris and almanac data), and the sat-nav number-crunches that to work out it's position by a sort of triangulation (more correctly - "trilateration").

Secondly, if you powered off the sat-nav for ANY time the satellites most certainly WOULD have moved! They are not geo-stationary, they are whizzing round at about 8,300 miles an hour, making two orbits a day.

What methods like Quickfix do is allow the unit to use published ephemeris data, before it has had time to collect the real thing from the satellites.

DrRobin · Occasional Visitor Joined: Apr 25, 2006 Posts: 14

Hi,

I appear to have encountered a similar problem but with a Binatone T430. I hadn't used the unit for a couple of weeks and when I did, it would find satellites but wouldn't compute a position. I assumed that it had lost it's almanac, which it should refresh from the satellite, but can take some time.

I left the unit on over-night in a position with a clear view of the sky. The next morning it had a position and now finds it's position very quickly even after a full shut down. I do however, have a problem with GPS time, it is reading year 18203 and some of the times aren't valid (E.g. hour 37).

I spoke to Binatone nd they told me that updates to the GPS system are causing problems with some receivers and they told me this started last week. These problems include loss of position and time and problems calculating position. I am a little sceptical of what they told me so decided to check it out for myself and there may be some truth in it, see link below:

http://sidt.gpsworld.com/gpssidt/Latest+News/New-GPS-Satellites-Problems-Indicated/ArticleStandard/Article/detail/596465

Apparently not all GPS chipsets suffer the problem and the only real issue appears to be when the GPS looses it's almanac (switched off or low battery for a long period of time) but it is very annoying.

I asked if there would be a fix for the GPS receiver if this turns out to be a permanent problem but they guy I spoke to wouldn't comment.

I have just compared this with another GPS receiver, which shows almost exactly the same position but displays the correct time. The chipset in the T430 is MStar.

I am bit worried that the unit packs up altogether and if there is no fix then I am left with a duff unit.

Regards

DrRobin

DrRobin · Occasional Visitor Joined: Apr 25, 2006 Posts: 14

Hi,

Apparently there has been a change to the NEMA output from the satellites and the MStar chipset doesn't correctly decode this.

MStar have apparently released a patch which fixes the problem but in most cases you need to get this patch from the manufacturer's of the Sat Nav.

If the MStar chip has correct time apparently it doesn't output any position at all. If like me I have managed to dump the almanac then it will output correct position data but the time flips every second.

My T430 is flipping between 27/1/18216 and 1/1/1601. I am asking Binatone for a patch.

I simply don't know how many other devices use the MStar chip set, worth a check in the specs if your Sat Nav isn't working.

Regards

DrRobin

george57l · Posted: Tue Jun 23, 2009 10:00 pm Post subject:

My better half came home tonight complaining her TT One stopped getting a satellite signal today while she was out. It has never been updated, changed, connected to TT Home or otherwise altered in any way from out-of-the-box. I've had this from time to time with my TT 500 and it usually recovers after a while or a reset.

Have reset the TT One (despite it not having a reset hole - apparently one has to press the power button for 30 secs) and it still sees no sats.

Anyone any ideas? Purely coincidental? (Re the last comments re Mstar?)

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