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Pocket GPS World :: View topic - Navman 3450 in France and poor lock no signal in mountains
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Navman 3450 in France and poor lock no signal in mountains

 
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gregh
Regular Visitor


Joined: 27/04/2003 17:15:12
Posts: 129
Location: United Kingdom

PostPosted: Wed Dec 03, 2003 2:21 pm    Post subject: Navman 3450 in France and poor lock no signal in mountains Reply with quote

so as a long term old Navman sleeve with TomTom, I took advantage of the recent 199 offer to get a new sleeve and tried out the Navman software.

I was travelling from Geneva to Val D'Isere for some skiing.

The initial lock on in France was horrible, around 1 hour, then as we got near the mountains it lost it's lock and couldn't lock on.

The same thing coming back, it took around an hour to lock on, only once we had left the mountains.

Is there something faulty or is this expected behaviour?
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Dave
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Joined: Sep 10, 2003
Posts: 6460
Location: UK

PostPosted: Wed Dec 03, 2003 2:35 pm    Post subject: Reply with quote

Make sure you don't drive until you have a fix, that will help, Is it the 3450 you have, with the external antenna socket ? If so, these are much better than previous sleeves and shouldn't experience too much problems.
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gregh
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Joined: 27/04/2003 17:15:12
Posts: 129
Location: United Kingdom

PostPosted: Wed Dec 03, 2003 2:41 pm    Post subject: Reply with quote

yes it's the one with the external socket. The first time we were sat still for 30-45 mins.

Also why would it drop out in the mountains? I thought some people used GPS in the mountains for walking etc.

regards,

greg
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Dave
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Joined: Sep 10, 2003
Posts: 6460
Location: UK

PostPosted: Wed Dec 03, 2003 3:08 pm    Post subject: Reply with quote

It shouldn't really drop out in the mountains, generally the higher up you get, the less multipath errors you will see down to rebounded signals off of tall buildings, if you're low in the valleys then you will probably see multipath errors, and this can cause signal problems.

The 3450 sleeve should be much better and less prone to having long TTFF's, a number of other things could have been the cause like local interference on or around the same frequency, whether you had a clear view of the sky, the clock being out by an hour or more on your Pocket PC or many other things. The main problems with the Navman Sleeves (and actually this was one of the main reasons for starting this website!) was that the sleeve is far too close to the iPAQ. What happens is that the GPS chip sometimes gets interference (RF Noise) from the iPAQ processor, and this can cause you to lose GPS data and extend the fix. A cold fix, e.g. 4+ hours when the receiver has been off for, should take 50 seconds, if it doesn't receive all the information from at least 4 satellites by this time, it can extend itself. That's the Ephemeris tables. If however somethings gone wrong on the sleeve and the backup battery isn't storing Almanac table then it could take 12.5 mins to obtain a fix, and if it doesn't get all of the data correct in this time frame, it could take a lot longer.

It's hard to tell on the odd occasion when things like this happen, it's much easier to diagnose and fault find (like most things) if you can duplicate the problem time and time again and perform a process of elimination.

The 3450 sleeves were much better and do have a military grade crystal which is supposed to help with the fix, but the sleeve is very close to the iPAQ. Another way other people surfing the forums have found is to take an old antistatic hard drive back and fold this up and put it between the sleeve and iPAQ and this can dampen the RF noise (the reflective kind of bags).

Generally speaking in the past Navman sleeves haven't performed as well as most GPS Receivers, the 3450 does acquire fixes much qiucker than the older 3000 and 3400 sleeves.

The easiest way if you do have time is to make sure you have WinFast Navigator installed, learn about what each GPS sentence means and you can fault find a little more when you experience problems like this.
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gregh
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Joined: 27/04/2003 17:15:12
Posts: 129
Location: United Kingdom

PostPosted: Wed Dec 03, 2003 3:25 pm    Post subject: Reply with quote

thanks for the detailed reply.

I guess the ipaq clock would have been on UK time.
and the vehicle had it's own GPS system (but with Swiss maps) so maybe that was causing inteference?

We were using the GPS status to watch it get between 2-7 satellites for the 45 mins it took to lock on.

I'll look into getting Winfast.

regards

greg
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Steveee
Lifetime Member


Joined: Dec 16, 2003
Posts: 203
Location: Colchester, Essex

PostPosted: Wed Dec 17, 2003 12:31 am    Post subject: Reply with quote

I've just bought a new Navman3450. I used it successfully and it worked straight out of the box. I used it on a recent trip to a Heathrow hotel with no problems. :D

Overnight I used the Ipaq 3850 for planning the next days route, games and diary!

The next morning it reported no satellite signal despite seeing 7 satellites the night before. Confused

I used the reset button and received the 7 satellites again within 30 seconds. :D

Looks as though the Ipaq may loose some files when used for other applications.

Regards

Steveee
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