[time-nuts] Characterising frequency standards
Steve Rooke
sar10538 at gmail.com
Wed Apr 8 12:27:28 UTC 2009
Bruce,
I hear what you say but the results seem to correlate quite well:-
1 tau, 3.0127e-009 adev(n=399998), 3.0127e-009 oadev(n=399998)
1 tau, 3.0257e-009 adev(n=199998), 3.0257e-009 oadev(n=199998)
And using the first half of the data:-
1 tau, 3.0411e-009 adev(n=199998), 3.0411e-009 oadev(n=199998)
So I'm trying to understand why this won't work.
73,
Steve
2009/4/9 Bruce Griffiths <bruce.griffiths at xtra.co.nz>:
> 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 <bruce.griffiths at xtra.co.nz>:
>>
>>> 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 <tvb at leapsecond.com>:
>>>>
>>>>
>>>>> 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
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>> and follow the instructions there.
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
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>>>
>>
>>
>>
>>
>
>
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--
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet
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