Another GPS problem?
rcw.schaller at web.de
Sat Aug 23 20:06:16 CEST 2008
I have to report another GPS problem. I'm quite unsure, but I guess it's
only a problem of my GTA02 and no general problem, but I'd like to hear
your opinion on this before I send back my device.
First I have to tell that the sd card IS ALREADY REMOVED!!!
After I discovered this problem, I followed this howto
(http://wiki.openmoko.org/wiki/Howto_Test_Your_GPS_with_agpsui) to be
sure its not a simple mistake of mine.
Well now to the problem itself. It takes a real long time to get a first
fix. Usually it takes about 250 to 400 second TTFF outside with blue
sky, but I also had 900+ seconds. The shortest TTFF I ever got were 96
seconds. That's far away from the data sheet of the U-blox ANTARIS 4
ATR0635. Under the same conditions the GTA02 takes its usual TTFF, my
GPS mouse (Sirf III chipset) takes about 40 seconds to get a fix.
Once the Freerunner has a fix the signal levels are about the same as
the ones my mouse gives (the highest are about -130dbm), so I guess the
problem is not a bad connected antenna.
But during the search for satellites they are like “frozen”. The GPS
discovers the first satellites about 10s after power on and displays
them with a level about -155dbm, but this level is frozen. It doesn't
change a bit for minutes and covering the device with your hand doesn't
have an effect on the level. After a while(about 3-4min after discovery)
the satellites one by one getting out of this frozen state and suddenly
rise to their normal levels. As soon as they are unfrozen, they change a
bit every few seconds and when you cover the device with a hand you can
see a clear decrease of the levels of the satellites that are already
unfrozen (the frozen ones still don't react).
Also the HDOP seems to be very high to me. Short after the first fix
it's about 10 to 7, after a while it is getting to 2.5 to 2. The GPS
mouse placed next to it is about 1.5 to 1.
And you can easily get the GTA02 to loose the fix, for example the mouse
I can put into my trouser pocket without loosing its fix, but the
freerunner than loses its fix by doing this longer than about one
minute. When you take it out again the next good fix takes not long,
maybe about 5 seconds.
I haven't disassembled the device yet to look for the antenna or
something, but I'm not going to do this on my one during the guarantee
I haven't tried an external antenna, because I do not own one and do not
want to buy one only for this purpose.
After all this testing I am on the verge to blame the GPS module or
maybe also the antenna.
My serial number is 8A8603100, date code 20080626.
Hay anyone ever seen a similar problem? Did I something wrong or can I
try something else?
P.S.: Please remember, the sd card is ALREADY REMOVED!!!
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