[time-nuts] GPS Locked and Unlocked Performance Comparison

Didier Juges didier at cox.net
Wed Feb 13 01:06:12 UTC 2008


To me, the interesting part is that both the Thunderbolt and the Miller
designs appear to degrade the performance of the OCXO in locked mode at
short Tau compared to unlocked. The Z3801 does very well < 300sec, but
degrades the ADEV at Tau farther out. The Fury does best, never worse locked
than unlocked. The practical difference between the Fury and Z3801 at short
Tau looks to be mostly in the OCXO, the Fury is the one that actually has
the least degradation of the OCXO performance overall.

Performance at short Tau cannot be better locked than unlocked, so it is
driven by the OCXO and software, but the fact that two designs (we will
forgive the Miller design, which looks to be mated to a very good OCXO, but
the Thunderbolt is less excusable) actually degrade the ADEV at short Tau is
surprising to me.

Didier KO4BB 

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Brian Kirby
> Sent: Tuesday, February 12, 2008 6:57 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] GPS Locked and Unlocked Performance 
> Comparison
> 
> 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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