[time-nuts] Characterising frequency standards

[Ulrich Bangert]

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. 

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.

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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