[Loadstone] GPS Receivers

[Rob Melchers]

Hi all, some more notes on receivers,

After having read different reports by users of the QStarz Q818 (MTK 
chipset) we had a look at the specs. We couldn't find any reliable data on 
SN or sleep mode. We have tested a receiver that uses the MTK chipset (the 
iBlue 737) and noticed that this receiver reports a large number of usable 
satellites (sometimes 13). However, lots of satellites don't guarantee 
better reception. If a satellite is two degrees over the horizon its 
presence in the calculation is of little value. The MTK chipset also 
promises a high sensitivity (-158 dBm). Again, this may help under certain 
circumstances but be a disadvantage under other. Therefore high sensitivity 
and lots of satellites reported don't qualify a receiver for use with 
Loadstone-GPS.

The iBlue 737 worked well when used in speeds over 5 KpH. Lower speed 
showed inaccurate data being sent from the receiver to the phone. The log 
we studied was taken on a walk in two main directions, a turn in the middle 
of 90 degrees. The first 5 minutes reported the opposite direction and the 
receiver reported a speed of 103 KpH. Only after several minutes the data 
confirmed with the actual situation, but still issued long streams of 
non-changing information, a sign of activated sleep mode. Also position 
reporting was not reliable (with errors of almost 100 yards). Since at this 
moment there is no way to change or look at the manufacturers settings we 
assume that this receiver has a high SN ratio set or goes into sleep mode 
when used at low speed. Buffered information from a previous trip is fed 
into the phone and results in unreliable information.

This does not mean that the MTK chipset is not able to perform well for our 
purposes, but if a manufacturer sets a number of settings to show a 
'smooth' track and a high mumber of satellites pedestrian use is 
prohibited. Please take this into account when purchasing a new receiver. 
If possible, take the receiver for a test run at low speed before you 
decide to buy it. The ideal test run is a 6 minute walk starting in one 
direction (preferably to the south) and making a right or left turn after 
three minutes while checking direction and speed every 30 seconds. If an 
owner of a receiver that uses the MTK chipset could send us a log of such a 
walk we could analyze the results even more accurate. A written report that 
states direction, duration and curving is mandatory for us to be able to 
make conclusions.

Windows users who want to do their own testing can e-mail me off-list, I'll 
try to assist in setting-up your own testing facility.

I don't know about the US, but in Europe you can return a product within 8 
days for a complete refund when buying of the web. So don't wait too long 
with testing.

If you want to play it safe, the Royaltec 20 and 21 series have proven to 
work fine with Loadstone-GPS, both in accuracy and Bluetooth connectivity. 
In Europe the AD750 and 800 by Adapt are more readily available and work 
fine too.

Rob


At 5/23/2007, you wrote:
>I have had good luck with the Royaltec RBT-2000.  I have also heard good
>things about the RBT-2100.  I just ordered the QStarz Q818.  Other people
>who use Loadstone have said good things about it.  I haven't used it.  I
>heard it goes into sleep mode at slow speeds.  I don't know how that will
>affect me or how it pairs with a Nokea 6680 at this time.
>
>
>Mike Hanson
>
>
>
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>Loadstone mailing list
>Loadstone at loadstone-gps.com
>http://www.loadstone-gps.com/mailman/listinfo/loadstone
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