[time-nuts] GPS Locked and Unlocked Performance Comparison

[SAIDJACK at aol.com]

Hi Kirby, Didier,
 
I agree, the short term performance (typically <200s or so) is almost  
entirely determined by the OCXO performance itself.
 
That particular Miller OCXO is exceptionally good in terms of short  term 
stability, I am surprised that the OCXO can perform so well <1000s  free-running.
 
For longer hold-over periods one would need to electronically compensate  for 
Aging-drift, temperature compensation, and other drifts to establish  good 
ADEV for intervalls >5000s or so, and this does not seem to be done  on the 
Miller and Thunderbolt units.
 
Of course the Z3801A is the Grand-Daddy OCXO of them all. The Z3801A does  
seem to have some short term noise issue compared to the others, maybe it's due  
to the Sigma-Delta modulation on its DAC?
 
It seems that the measurement below 0.2s intervalls is limited by the  
measurement equipment since all (except Z3801A) units seem to have identical  
performance <0.2s intervalls?
 
bye,
Said
 
 
 
 
In a message dated 2/12/2008 16:57:28 Pacific Standard Time,  
kirbybq at bellsouth.net writes:

Its  interesting that the Miller/Jupiter design appears to outperform  
everything except the Z3801, in the GPS locked modes.  Maybe the KISS  
principle at work.

SAIDJACK at aol.com wrote:
> Hello  Tom,
>  
> excellent web-page! That looks like a lot of work  was done.
>  
> Would you have data for 24 hour hold-over  performance (86400s ADEV)  for 
> these units?
>   
> thanks,
> bye,
> Said
>  
>   
> In a message dated 2/11/2008 21:17:49 Pacific Standard Time,   
> tvb at LeapSecond.com writes:
>
> Sifting  through old  data, in addition to recent measurements
> made in the past few   months, I have 4 very interesting plots
> of GPSDO  performance.
>
> The  goal was to see real-life plots of  disciplining in action by
> contrasting  free (unlocked) vs.  GPS-locked performance as
> compared with my 10 MHz house   reference. The four GPSDO
> measured so far are: Z3801A, Fury,  Thunderbolt,  and Miller.
>
>  http://www.leapsecond.com/pages/gpsdo/
>
> Comments  &  questions welcome.
>
> I hope to measure quite a few more this  year.  Contact me
> offline if you want your favorite one included  in the list.  Note
> that I'm not necessarily looking for the best  GPSDO; instead,
> for  this page at least, the more variety  the  better.
>
> /tvb
>
>
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**************The year's hottest artists on the red carpet at the Grammy 
Awards. Go to AOL Music.      
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