thomas at gstaedtner.net
Mon Jul 14 15:05:56 CEST 2008
On Mon, Jul 14, 2008 at 10:45 AM, Kalle Kärkkäinen <
kalle.karkkainen at intstream.fi> wrote:
> In my past life I developed a fleet management device that had GPS and
> GSM in it, able to send the fix data to server in intervals. we even
> implemented some location alerts (around the vicinity of, or near
> Based on that experience, we used on of falcoms devices for it, it most
> probably did not have much of a cache for gps data (black box, tough to
> tell), but it needed a strong antenna for gps. For a GSM antenna you
> could use a hairpin, anything that had 10-15 cm of length was totally
> enough for good quality gsm connection. GPS required much more, in our
> case we supplied all the devices with external antennas.
> My knowledge is based solely on this work experience, I'm no radio-geek
> so I cant really tell much about antennas and signal catching. What kind
> of GPS-antenna is there in FR? Embedded for sure, but could that be the
> I guess your TomTom comes with an external windshield antenna?
No, it has no external antenna, only a window-mount with antenna connector
but without one connected.
That GSM works better is sure, because mobile GSM devices can receive at
-110 dBm (usually ~ -70 to -90) while GPS chips receive at up to -160 dBm
(usually between -130 and -150 at the antenna).
I think the antenna in the freerunner is not that bad, it even has a preamp.
Ublox can receive at -158 dBm (according to the datasheet), what is pretty
good (and definitely not worse than every good navigation device), and
should get at least -130 dB (good enough for a cold boot fix) _after_ the
antenna (preamplified) I guess. It even has it's own additional amp on chip.
So the problem is imho only bad build quality (QA) at least in some of the
devices (might be a defect connector by 3rd party, don't know).
Short version: antenna good (I bet it's better than the antennas in most
other smartphones with GPS), chip very good -> bug.
And btw. - SIRF Star III are damn good chips and used in many navigation
devices and bluetooth gps devices, but the antaris is almost at the same
It surely is no software issue, theoretically it could be a firmware issue
of the u-blox, but I don't think it is.
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