[time-nuts] Some long-term data

Magnus Danielson cfmd at bredband.net
Sun Dec 24 22:04:09 EST 2006


From: Magnus Danielson <cfmd at bredband.net>
Subject: Re: [time-nuts] Some long-term data
Date: Mon, 25 Dec 2006 03:43:16 +0100 (CET)
Message-ID: <20061225.034316.-1476063739.cfmd at bredband.net>

> Now, I made a quick little program that process the data, here is the result:

Ehum... no... forget those plots. I just realized a little error in my
drift(tau) estimator. I had a divide by tau too little, which will make the tau
rise. As I said, the devil is in the details.

Corrected it becomes the less interesting plots:

magnus at heaven:~/febo$ ./process cs1-gps.dat
Processing cs1-gps.dat
f = -1.371312943e-13
d = -2.464638917e-19
  tau         ADEV             drift       ADEV drift corr
    600  6.669673909e-12 -2.464638917e-19  6.669673909e-12
   1200  3.834415574e-12 -8.108122133e-20  3.834415574e-12
   3000  2.262840286e-12 -2.392890882e-19  2.262840286e-12
   6000  1.321830189e-12 -3.349535739e-20  1.321830189e-12
  12000  6.871654621e-13 +3.846473719e-20  6.871654621e-13
  30000  3.721752717e-13 +2.056358286e-20  3.721752717e-13
  60000  2.376494277e-13 -1.810085678e-20  2.376494276e-13
 120000  1.702980952e-13 +2.320652509e-21  1.702980952e-13
 300000  1.549264955e-13 +3.629179727e-21  1.549264954e-13
 600000  1.401676798e-13 -5.790456326e-21  1.401676797e-13
1200000  6.799762269e-14 +1.948183423e-20  6.799761934e-14
3000000  1.010049262e-13 +4.150533462e-20  1.010049006e-13
6000000  1.550028203e-13 +3.651598399e-20  1.550027944e-13
magnus at heaven:~/febo$ ./process cs2-gps.dat
Processing cs2-gps.dat
f =  5.853529458e-13
d =  1.816049729e-19
  tau         ADEV             drift       ADEV drift corr
    600  7.508211487e-12 +1.816049729e-19  7.508211487e-12
   1200  4.527916555e-12 +9.729746560e-20  4.527916555e-12
   3000  2.722308557e-12 +4.515867825e-20  2.722308557e-12
   6000  1.721060210e-12 -7.880496874e-20  1.721060210e-12
  12000  1.035443547e-12 +9.560956213e-20  1.035443547e-12
  30000  6.178807446e-13 +1.132639019e-19  6.178807443e-13
  60000  4.117968150e-13 +1.218708103e-19  4.117968139e-13
 120000  2.667708446e-13 +8.332110720e-20  2.667708431e-13
 300000  1.831015144e-13 +7.249210859e-20  1.831015101e-13
 600000  1.607481137e-13 +6.187329751e-20  1.607481066e-13
1200000  9.695302954e-14 +6.246924523e-20  9.695300539e-14
3000000  1.780291901e-13 +7.356014755e-20  1.780291445e-13
6000000  3.223233857e-13 +7.588775895e-20  3.223233321e-13
magnus at heaven:~/febo$ ./process rb1-gps.dat
Processing rb1-gps.dat
f =  1.081017978e-14
d = -4.280688646e-19
  tau         ADEV             drift       ADEV drift corr
    600  6.497785589e-12 -4.280688646e-19  6.497785589e-12
   1200  3.673171557e-12 -5.189198165e-20  3.673171557e-12
   3000  2.152493532e-12 -3.462165333e-19  2.152493532e-12
   6000  1.229699919e-12 -1.347603914e-19  1.229699919e-12
  12000  5.983794472e-13 -2.793891384e-20  5.983794472e-13
  30000  3.088139889e-13 -1.001855674e-19  3.088139884e-13
  60000  2.375139899e-13 -1.183043196e-19  2.375139881e-13
 120000  2.408230821e-13 -9.341989437e-20  2.408230800e-13
 300000  2.703779963e-13 -5.825801115e-20  2.703779944e-13
 600000  2.336053294e-13 -5.052904535e-20  2.336053261e-13
1200000  1.439223207e-13 -3.937365625e-20  1.439223143e-13
3000000  1.847594665e-13 -6.727980125e-20  1.847594298e-13
6000000  2.953067943e-13 -6.935111621e-20  2.953067454e-13

You do that drift corrections do change the numbers a bit. The distance is
however so large that for these numbers we can safely ignore drift correction.

There is a subtle point in the drift(tau) calculation, it is designed to
model the ADEV(tau) sensitivity to drift, rather than just using the overall
drift averaging. The overall drift averaging may however be a good indicator
on weither drift compensation is needed or not. With an alternative form of
ADEV can all three measures be calculated concurrently and with a much
smaller memory usage than keeping all samples and post-process it.

Cheers,
Magnus




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