Yes, we have yet another proof that the oscillator in (cheap?) GPS receivers can be a source of troubles... shall we start to design Ovenized GPS Receivers (OGPR) too? Or ovens for GPS receivers.
On Fri, Dec 28, 2012 at 11:35 PM, Bob Camp <[email protected]> wrote: > Hi > > The GPS does an estimate against the local crystal frequency. It generates > the PPS off of it's estimate. The less often it updates the estimate the > more odd things you see as the crystal drifts. > > Of course, the crystal can have trouble all it's own. If the crystal has a > rapid rate of frequency change over a narrow temperature range, the GPS > simply can't keep up with the crystal. > > Bob > > On Dec 28, 2012, at 5:27 PM, Fabio Eboli <[email protected]> wrote: > > > Like I mentioned in a precedent message > > (answering Magnus) I'm seeing some temp > > effects on my GPS module, see this message: > > http://www.febo.com/pipermail/time-nuts/2012-December/073310.html > > > > In this graph there are the FE5680 voltages > > and temperatures, and the temperature sensed > > on the PCB near the GPS: > > http://www.flickr.com/photos/14336723@N08/8318815981/ > > > > At time 20000s I heated the GPS receiver directly > > with hot air gun and the drift started to change > > rapidly. > > At 25000 I heated the FE5680#2 I was using > > as reference, but no visible effects, (apart > > the slight variation in it's voltage :) > > At 30000 33000 35000 seconds I heated the > > GPS with a resistor placed near the PCB, > > this generated more gradual temperature > > variation on the GPS. > > > > Here can be seen the results of the heating > > on the drift, (logging GPS PPS against Rb): > > http://www.flickr.com/photos/14336723@N08/8318816213/ > > the hotair generated so much variation, that > > the script was unable to unscrable the data. > > The resistor heater generated slower temperature > > variation on the GPS, it's visible a glitch > > everytime there was a temperature variation, > > and the drift magnitude seem to follow the > > variation of the temperature in time (dT/dt). > > > > I will try to reduce temperature sensivity > > incrementing the thermal capacitance and > > isolating the GPS from the ambient. > > > > Is this normal or it's a defect ("feature") of > > my unit? I'm also curious about what internal > > structure can generate this wander in PPS. > > Like I said before it's like if the PPS pulse > > (for intervals of few 100's of nS) depends on > > something that is very temperature dependent. > > > > Thanks, > > Fabio. > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
