Steve It cant, it must be a matter of interpretation. Perhaps it means something like:
1 tau means tau = 1x the interval between consecutive measurements. 2 tau means tau = 2x the interval between consecutive measurements 100000 tau means tau = 100,000 x the interval between consecutive measurements Bruce Steve Rooke wrote: > Bruce, > > But how does that explain the output of Tom's adev1 program which > still seems to give a a good measurement at tau = 1s? > > 73, > Steve > > 2009/4/8 Bruce Griffiths <[email protected]>: > >> Steve >> >> If you delete every second measurement then your effective minimum >> sampling time is now 2s and you can no longer calculate ADEV for tau< 2s. >> You can still calculate ADEV for tau = 100,000 sec. >> >> If you delete all but the first 200,000 lines then you can calculated >> ADEV for tau=1sec and up to tau= 25,000 sec with reasonable accuracy. >> >> You shouldn't lose sight of the fact that ADEV and OADEV are both >> estimates of the Allan deviation. >> >> >> Bruce >> >> Steve Rooke wrote: >> >>> Tom, >>> >>> I understand fully the points that you have made but I have obviously >>> not made my point clear to all and i apologise for my poor >>> communication skills. >>> >>> This is what I'm getting at: >>> >>> Using your adev1.exe from http://www.leapsecond.com/tools/adev1.htm >>> and processing various forms of gps.dat from >>> http://www.leapsecond.com/pages/gpsdo-sim/gps.dat.gz. >>> >>> C:\Documents and Settings\Steve Rooke\Desktop>adev1.exe 1 <gps.dat >>> >>> ** Sampling period: 1 s >>> ** Phase data scale factor: 1.000e+000 >>> ** Total phase samples: 400000 >>> ** Normal and Overlapping Allan deviation: >>> >>> 1 tau, 3.0127e-009 adev(n=399998), 3.0127e-009 oadev(n=399998) >>> 2 tau, 1.5110e-009 adev(n=199998), 1.5119e-009 oadev(n=399996) >>> 5 tau, 6.2107e-010 adev(n=79998), 6.1983e-010 oadev(n=399990) >>> 10 tau, 3.1578e-010 adev(n=39998), 3.1549e-010 oadev(n=399980) >>> 20 tau, 1.6531e-010 adev(n=19998), 1.6534e-010 oadev(n=399960) >>> 50 tau, 7.2513e-011 adev(n=7998), 7.3531e-011 oadev(n=399900) >>> 100 tau, 4.0029e-011 adev(n=3998), 4.0618e-011 oadev(n=399800) >>> 200 tau, 2.1512e-011 adev(n=1998), 2.1633e-011 oadev(n=399600) >>> 500 tau, 9.2193e-012 adev(n=798), 9.1630e-012 oadev(n=399000) >>> 1000 tau, 4.9719e-012 adev(n=398), 4.7750e-012 oadev(n=398000) >>> 2000 tau, 2.6742e-012 adev(n=198), 2.5214e-012 oadev(n=396000) >>> 5000 tau, 1.0010e-012 adev(n=78), 1.1032e-012 oadev(n=390000) >>> 10000 tau, 6.1333e-013 adev(n=38), 6.1039e-013 oadev(n=380000) >>> 20000 tau, 3.8162e-013 adev(n=18), 3.2913e-013 oadev(n=360000) >>> 50000 tau, 1.0228e-013 adev(n=6), 1.5074e-013 oadev(n=300000) >>> 100000 tau, 5.8577e-014 adev(n=2), 6.7597e-014 oadev(n=200000) >>> >>> So far, so good. Now I delete every even line in the file which leaves >>> me with 200000 lines of data (400000 lines in original gps.dat file). >>> (awk 'and(NR, 1) == 0 {print}' <gps.dat >gps1.dat) >>> >>> C:\Documents and Settings\Steve Rooke\Desktop>adev1.exe 1 <gps1.dat >>> >>> ** Sampling period: 1 s >>> ** Phase data scale factor: 1.000e+000 >>> ** Total phase samples: 200000 >>> ** Normal and Overlapping Allan deviation: >>> >>> 1 tau, 3.0257e-009 adev(n=199998), 3.0257e-009 oadev(n=199998) >>> 2 tau, 1.5373e-009 adev(n=99998), 1.5345e-009 oadev(n=199996) >>> 5 tau, 6.3147e-010 adev(n=39998), 6.3057e-010 oadev(n=199990) >>> 10 tau, 3.3140e-010 adev(n=19998), 3.3067e-010 oadev(n=199980) >>> 20 tau, 1.7872e-010 adev(n=9998), 1.7810e-010 oadev(n=199960) >>> 50 tau, 7.9428e-011 adev(n=3998), 8.1216e-011 oadev(n=199900) >>> 100 tau, 4.2352e-011 adev(n=1998), 4.3265e-011 oadev(n=199800) >>> 200 tau, 2.2001e-011 adev(n=998), 2.2593e-011 oadev(n=199600) >>> 500 tau, 9.6853e-012 adev(n=398), 9.5441e-012 oadev(n=199000) >>> 1000 tau, 5.0139e-012 adev(n=198), 5.0387e-012 oadev(n=198000) >>> 2000 tau, 2.7994e-012 adev(n=98), 2.7090e-012 oadev(n=196000) >>> 5000 tau, 1.4280e-012 adev(n=38), 1.2214e-012 oadev(n=190000) >>> 10000 tau, 7.4881e-013 adev(n=18), 6.5814e-013 oadev(n=180000) >>> 20000 tau, 7.6518e-013 adev(n=8), 3.7253e-013 oadev(n=160000) >>> 50000 tau, 2.4698e-014 adev(n=2), 1.3539e-013 oadev(n=100000) >>> >>> Obviously we don't have enough data now for a measurement of 100000 >>> tau but the results for the other tau are quite close, especially when >>> there are sufficient data points. Now this is discontinuous data, >>> exactly what I was trying to allude to. >>> >>> OK, so now I take only the top 200000 lines of the gps.dat file (head >>> -200000 gps.dat >gps2.dat) >>> >>> C:\Documents and Settings\Steve Rooke\Desktop>adev1.exe 1 <gps2.dat >>> >>> ** Sampling period: 1 s >>> ** Phase data scale factor: 1.000e+000 >>> ** Total phase samples: 200000 >>> ** Normal and Overlapping Allan deviation: >>> >>> 1 tau, 3.0411e-009 adev(n=199998), 3.0411e-009 oadev(n=199998) >>> 2 tau, 1.4985e-009 adev(n=99998), 1.4999e-009 oadev(n=199996) >>> 5 tau, 6.1964e-010 adev(n=39998), 6.2010e-010 oadev(n=199990) >>> 10 tau, 3.1315e-010 adev(n=19998), 3.1339e-010 oadev(n=199980) >>> 20 tau, 1.6499e-010 adev(n=9998), 1.6495e-010 oadev(n=199960) >>> 50 tau, 7.1425e-011 adev(n=3998), 7.3416e-011 oadev(n=199900) >>> 100 tau, 3.9940e-011 adev(n=1998), 4.0730e-011 oadev(n=199800) >>> 200 tau, 2.1488e-011 adev(n=998), 2.1558e-011 oadev(n=199600) >>> 500 tau, 8.4809e-012 adev(n=398), 9.0886e-012 oadev(n=199000) >>> 1000 tau, 4.9223e-012 adev(n=198), 4.7104e-012 oadev(n=198000) >>> 2000 tau, 2.4335e-012 adev(n=98), 2.4515e-012 oadev(n=196000) >>> 5000 tau, 1.0308e-012 adev(n=38), 1.0861e-012 oadev(n=190000) >>> 10000 tau, 5.9504e-013 adev(n=18), 6.1031e-013 oadev(n=180000) >>> 20000 tau, 3.6277e-013 adev(n=8), 3.1994e-013 oadev(n=160000) >>> 50000 tau, 1.0630e-013 adev(n=2), 1.6715e-013 oadev(n=100000) >>> >>> Is there any Linux tools for calculating adev as I'm having to run >>> Windows in a VMware session? >>> >>> 73, >>> Steve >>> >>> 2009/4/8 Tom Van Baak <[email protected]>: >>> >>> >>>> Steve, >>>> >>>> You've asked a couple of questions. Let me start with this. >>>> >>>> It is true that if one were only interested in the performance >>>> of a pendulum (or quartz or atomic) clock for averaging times >>>> of one day that all you would need is a series of time error >>>> (aka phase) measurements made about the same time once >>>> a day (doesn't have to be that exact). After one week, you'd >>>> have 7 error measurements (=6 frequency =5 stability points) >>>> and this is adequate to calculate the ADEV for tau 1 day. >>>> This alone allows you to rank your clock among all the other >>>> pendulum clocks out there. Note also you get time error and >>>> rate error from these few data points too. >>>> >>>> As another example, suppose you have a nice HP 10811A >>>> oscillator and want to measure its drift rate. In this case you >>>> could spend just 100 seconds and measure its frequency >>>> once a day, or even once every couple of days. Do this for >>>> a month and you'd have several dozen points. If you plot >>>> these frequency measurements you will likely see that they >>>> approximately fall on a line; the slope of the is the frequency >>>> drift rate of the 10811. The general shape of the points, or >>>> the fit of the line is a rough indication of how consistent the >>>> drift rate is or if it's increasing or decreasing. >>>> >>>> Neither of these examples require a lot of data. Both of these >>>> are real-world examples. >>>> >>>> OK so far? >>>> >>>> /tvb >>>> >>>> >>>> >>>> _______________________________________________ >>>> 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.
