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Poor GPS lock in Alfa Romeo 156 Sportwagon - windscreen ?

 
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Matrick
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PostPosted: Sat Jan 03, 2004 3:17 pm    Post subject: Poor GPS lock in Alfa Romeo 156 Sportwagon - windscreen ? Reply with quote

I'm using a IPAQ H2210 with TT2 and a Royaltek Sapphire receiver.

I have only been using this setup for 3 days and have run into GPS locking problems. Basically first lock can take 20 minutes (the worst case) but typically takes up to five minutes. Signal is frequently lost and takes a while to re-aquire. Today to prove a point I placed the receiver on the roof through an open window - perfect, immediate lock, with more satelites!

I therefore assume that the problem is due to the vehicles windscreen. Global Positioning Systems are sending me a Fortuna Clip On Bluetooth unit to try out.

I am hoping to install this in the boot of the car as there is a spare cigarette socket (then I don't have to worry about re-charging the battery - I can leave it permanently connected). Is the rear windscreen likely to give similar GPS lock problems as the front ?

Alternatively what other solutions are open to me. Re-radiating ariels? The problem here is that I don't really want to mount anything on the roof, so the same with a waterproof GPS receiver....

Any thoughts or ideas appreciated

Regards

Matt J
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Dave
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PostPosted: Sat Jan 03, 2004 3:45 pm    Post subject: Reply with quote

In that case it is the windscreen which is probably UV coated. Rear windscreen may be the same, but the only way would be to try a Bluetooth Receiver or something you can plug in, in the boot to test this for sure.

A re-rad is another option but it requires having an antenna on the roof of the car and also a powered accessory socket in use by the re-rad all the time.
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Matrick
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PostPosted: Sat Jan 03, 2004 5:24 pm    Post subject: Reply with quote

Thanks for the reply Dave.

I will try out the receiver in the boot and see what happens. With regard to the re-rad, can it be permantly installed, so that the antenna is always on the roof or does the antenna need to be placed each day ? How near does the antenna need to be to the GPS receiver?

Thanks in advance

Matt
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johnnyxx
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PostPosted: Sun Jan 04, 2004 5:43 am    Post subject: Reply with quote

i have the bluetooth reciever and i was told about the windscreen having a front heated windscreen is meant to block the sats seeing the gps reciever. but mine works ok i get about 6 to 8 sats seeing me all the time. can u not wire it to your arial so you get a stronger signal ?
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Dave
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PostPosted: Sun Jan 04, 2004 9:48 am    Post subject: Reply with quote

Matrick wrote:
Thanks for the reply Dave.

I will try out the receiver in the boot and see what happens. With regard to the re-rad, can it be permantly installed, so that the antenna is always on the roof or does the antenna need to be placed each day ? How near does the antenna need to be to the GPS receiver?

The Re-Rad could permanently be powered, it just means it will be re-radiating a signal inside the car all the time when there's nothing there to grab the signal. No real problem I guess.

You need to be within 45cm of the antenna (inside). Basically you'll have an external antenna and an internal antenna. Take a look at http://www.pocketgpsworld.com/reradiating.php
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Dave
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PostPosted: Sun Jan 04, 2004 9:51 am    Post subject: Reply with quote

johnnyxx wrote:
i have the bluetooth reciever and i was told about the windscreen having a front heated windscreen is meant to block the sats seeing the gps reciever. but mine works ok i get about 6 to 8 sats seeing me all the time. can u not wire it to your arial so you get a stronger signal ?

There are two issues that will dampen signals, a UV coated windscreen, and a windscreen with a coil. A UV coated windscreen will seriously block signals and will require in 90% of cases a Re-Rad or placement of the antenna outside. A coil in the windscreen won't necessarily dampen the signal. It will but by a small percentage. Basically you are putting an electrical current through the wires in the windscreen, and anything like this will dampen a signal, but not to the extreme like a UV coated windscreen will. It really depends on whether the heater is on (current travelling through the coil), angle of windscreen and whether depending on how it's manufactured. Most people with coils can use a GPS without problems, but some can't.
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Matrick
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PostPosted: Sun Jan 04, 2004 1:34 pm    Post subject: Reply with quote

Dave

With regard to permanently mounting the re-rad external antenna, am I right in assuming that a hole needs to made in the vehicles roof ?

Regards

Matt
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Matrick
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PostPosted: Sun Jan 04, 2004 2:10 pm    Post subject: Reply with quote

I've just been talking to one of the techs at Global positioning Systems. He has informed me that there is an external antenna made by by Fortuna specifically for the clip on bluetooth unit. So for £20 I shall give it a try. I will be able to permanently power the bluetooth unit in the boot of the car (using the spare ciggarette socket) and run the external antenna to the roof running the cable shut in the boots door.

I'll let you know how it works.

Regards

Matt
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Dave
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PostPosted: Sun Jan 04, 2004 7:16 pm    Post subject: Reply with quote

The Re-Rad's always have a magentic base to the external antenna so no holes are needed. You should be able to get an external patch antenna (again which will have a magnetic base) but the cable length on these are only usually 1-2 meters.
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johnnyxx
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PostPosted: Mon Jan 05, 2004 2:12 am    Post subject: Reply with quote

so is 6 to 8 sats seeing me all the time any good then, i thought it was Laughing Out Loud.
and another thing on a route about 60 miles long it took my pda about 10 mins to calulate the route . and thats on fast routing my pda is a compaq 3970 , does this seem right . im new to all this as you can prob see
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Dave
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PostPosted: Mon Jan 05, 2004 9:44 am    Post subject: Reply with quote

johnnyxx wrote:
so is 6 to 8 sats seeing me all the time any good then, i thought it was Laughing Out Loud.
and another thing on a route about 60 miles long it took my pda about 10 mins to calulate the route . and thats on fast routing my pda is a compaq 3970 , does this seem right . im new to all this as you can prob see


7-9 sats is usually a good average. People who are experiencing difficulty with a satellite fix can find they will only get around 3, and fixes will take a long time. You should be okay. Route calculation depends on whether you have changed road speeds, the application you are using and how many minor roads in the vacinity could lead to navigating you to your ultimate destination, and the length of the journey. 10 mins is usually a bit of an overkill.
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Matrick
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PostPosted: Tue Jan 06, 2004 3:41 pm    Post subject: Reply with quote

Sorted!

I haven't yet tried the external antenna but using the Xtrac mode it works.

I have mounted the receiver, permanently to the rear cigarette socket, in the boot and am getting 7 - 10 satellite locks. Interestingly it was hit and miss in ST mode. It also worked the same in Xtrac when mounted on the dash, so it appears that the Xtrac mode can work with the UV windscreen anyway.

I have travelled on the M4 and through very built up areas of central London today and never once lost GPS lock, perfect Laughing

I will try the ST mode again with the external antenna but even if not, I do have a perfectly satisfactory solution.

Thanks for all the advice, it's well appreciated!

Regards

Matt
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Matrick
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PostPosted: Fri Jan 09, 2004 5:49 pm    Post subject: Reply with quote

I've just connected the Fortuna external antena and switched the unit back to the preferred ST mode:

8 to 12 satelite locks, very strong signals - now I'm really chuffed!

I definitely reccomend this antena, especially at only £20.00

Regards

Matt
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