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. > -- Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW Omnium finis imminet _______________________________________________ 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.
