[time-nuts] GPSDO simulation tool
Magnus Danielson
magnus at rubidium.dyndns.org
Sat Mar 22 20:34:05 EDT 2014
On 22/03/14 23:25, Lars Walenius wrote:
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> Many thanks Tom for an excellent tool and also the data you have provided. You don´t happen to have data for a non sawtooth corrected M12?
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> Another question: how do you insert the options for ticres and dacbits? With “gpsim1 avg1=10 gps-mtk3339.txt ocxo.dat >gpsdo.txt” I managed to get different prefiltering in the same way as you had in your graphs. But inserting dacbits=10 instead of avg1=10 gave an error for me.
To further illustrate this, I redid the ADEV plot (forgot I have 399999
samples and not 40000) and now for no, 10 ns, 100 ns and 1 us TIC
resolution.
Turns out that there is essentially no difference between no and 10 ns
resolution and doing just 100 ns has only a small impact that becomes
more distinct at longer taus. At 1 us this becomes more obvious.
Turning over to TDEV it becomes more clear what happens in the higher
taus, so we want to look more closely at it, so we turn to the phase
where we see how the TIC resolution has us scooter between the different
quantization steps when we get captured near one for a long time.
Lessons learned:
1) Too coarse TIC resolution can get us alternate between two stages,
separated by the TIC resolution.
2) TIC resolution near the noise of the GPS is sufficient to track it,
higher resolutions provides no significant gain.
No big surprise when you think about it.
Cheers,
Magnus
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