[time-nuts] Re: Question about GPS 1PPS ADEV

[Matthias Welwarsky]

On Samstag, 16. April 2022 19:20:57 CEST Matthias Welwarsky wrote:
> On Samstag, 16. April 2022 17:55:17 CEST John Ackermann N8UR wrote:
> > Finally, it looks like you're comparing the raw PPS with an oscillator
> > that is steered by that same PPS.  I have to think their correlation
> > could lead to possible and unpredictable errors.  It would be better to
> > have the OCXO remain unsteered during the measurement.
> 
> That's correct. But I'm not trying to characterize the OCXO or the GNSS
> receiver. I was just wondering about this perceived discrepancy.

Of course curiosity got the better of me. I switched the GPSDO to hold-over 
and recorded about 4000 seconds of data. Result is attached. BTW I terminated 
the experiment after the temperature compensation kicked the DAC one LSB down. 
I am quite pleased with the performance of the OCXO, though. I was not 
expecting that, it is really nothing special. Not a surplus Chinesium OCXO, 
but something you can buy for quite reasonable money from Digikey.

So, the bulge is getting a bit more prominent, but it is in no way as 
prominent as the figure 26 in John Ackermann's paper. 

John, what constellations did you have enabled during the test? Just GPS, or 
also others? I usually run with GPS and Galileo enabled (and I avoid GLONASS, 
it messes everything up). Can this make a difference?


> > Best,
> > John
> > ----
> > 
> > > Best regards,
> > > Matthias
> > > 
> > > https://hamsci.org/sites/default/files/publications/2020_TAPR_DCC/
> > > N8UR_GPS_Evaluation_August2020.pdf
> > > 
> > > 
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