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[time-freq] Re: Febo.com's Z3801A Performance

K&J Aggett kj.aggett at optusnet.com.au
Fri Jun 29 23:25:23 UTC 2007


Hi John,

I am curious about the regular, large jumps in offset shown in the 
Current Day graph.  These jumps are much larger than others that are 
present, suggesting that the minimum correction possible is of the order 
of 5 microseconds or so.  Now, assuming that the Z801A is performing 
well, we have a cosseted, high quality xtal oscillator which, apart from 
the relatively rare jump, should just drift gently along, requiring the 
occasional intervention of the controller to keep it on 
frequency/phase.  A further observation is that positive jumps are 
frequently followed by smaller negative jumps.  Over-correction 
somewhere perhaps?

Is there any indication as to what these jumps mean?  Are they 
representative of actual changes in the Z3801A output or are they 
introduced elsewhere else in the system?  I have been wondering about 
strange spikes on some of my monitoring, too, but as yet lack sufficient 
data to do more than wonder.


Keith Aggett



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> Hello!
> Our Owner has his TAPR FatPPS connected to a Soekris system running
> FreeBSD, and is making use of a Clock Block, for a better
> understanding of what I am getting at and why I am bringing up the
> merely obvious as opposed to the incredibly obvious, please revisit
> http://www.febo.com/pages/soekris/ it explains in far greater detail
> as to why I am doing that.
>
> Now the question, will the pair work with the same hardware but with
> it running Linux?
>
> I freely admit that I had known at the TAPR site because they were the
> first to offer in the US a board that translates a CF card into an IDE
> form facter gizmo, it was mentioned in a copy of either LinuxJournal,
> or their late ELJ newsletter that I have here. But that is an
> inredible job of making three objects work together and do something
> special. I should also mention that the Soekris people were also
> brought to my attention in an article in the same magazine on the
> subject of network managing a sump pump.
>
>   





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