[time-nuts] Characterising frequency standards
Steve Rooke
sar10538 at gmail.com
Fri Apr 10 10:54:39 UTC 2009
Ulrich,
2009/4/10 Ulrich Bangert <df6jb at ulrich-bangert.de>:
> Steve,
>
>> I think the penny has dropped now, thanks. It's interesting
>> that the ADEV calculation still works even without continuous
>> data as all the reading I have done has led me to belive this
>> was sacrosanct.
>
> The penny may be falling but it is not completely dropped: Of course you can
> feed your ADEV calculation with every second sample removed and setting Tau0
> = 2. And of course you receive a result that now is in "harmony" with your
> all samples / Tau0 = 1 s computation. Had you done frequency measurements
> the reason for this appearant "harmony" is that your counter does not show
> significant different behaviour whether set to 1 s gate time or alternate 2
> second gate time.
So why would my counter show any significant differences between a 1
sec or 2 sec gate time?
> Nevertheless leaving every second sample out is NOT exactly the same as
> continous data with Tau0 = 2 s. Instead it is data with Tau0 = 1 s and a
> DEAD TIME of 1s. There are dead time correction schemes available in the
> literature.
I've just done a Google search for "dead time correction scheme" and I
just turn up results relating to particle physics where it seems
measurements are unable to keep up with the flow of data, hence the
need to factor in the dead time of system. This form of application
does not appear to correlate with the measurement of plain
oscillators. Yes there is dead time, per say, but I fail to see how
this can detract significantly from continuous data given a sufficient
data set size (as for a total measurement time).
I guess what we need is a real data set which would show that this
form of ADEV calculation produces incorrect results, IE. the proof of
the pudding is in the eating.
73,
Steve
> Best regards
> Ulrich Bangert
>
>> -----Ursprungliche Nachricht-----
>> Von: time-nuts-bounces at febo.com
>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Steve Rooke
>> Gesendet: Donnerstag, 9. April 2009 14:00
>> An: Tom Van Baak; Discussion of precise time and frequency measurement
>> Betreff: Re: [time-nuts] Characterising frequency standards
>>
>>
>> Tom,
>>
>> 2009/4/9 Tom Van Baak <tvb at leapsecond.com>:
>> > The first argument to the adev1 program is the sampling
>> interval t0.
>> > The program doesn't know how far apart the input file samples are
>> > taken so it is your job to specify this. The default is 1 second.
>> >
>> > If you have data taken one second apart then t0 = 1.
>> > If you have data taken two seconds apart then t0 = 2.
>> > If you have data taken 60 seconds apart then t0 = 60, etc.
>> >
>> > If, as in your case, you take raw one second data and remove every
>> > other sample (a perfectly valid thing to do), then t0 = 2.
>> >
>> > Make sense now? It's still "continuous data" in the sense that all
>> > measurements are a fixed interval apart. But in any ADEV
>> calculation
>> > you have to specify the raw data interval.
>>
>> I think the penny has dropped now, thanks. It's interesting
>> that the ADEV calculation still works even without continuous
>> data as all the reading I have done has led me to belive this
>> was sacrosanct.
>>
>> What I now believe is that it's possible to measure
>> oscillator performance with less than optimal test gear. This
>> will enable me to see the effects of any experiments I make
>> in the future. If you can't measure it, how can you know that
>> what your doing is good or bad.
>>
>> 73,
>> Steve
>> --
>> Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
>> Omnium finis imminet
>>
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>
>
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--
Steve Rooke - ZL3TUV & G8KVD & JAKDTTNW
Omnium finis imminet
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