[time-nuts] FEI 5680A

Rex rexa at sonic.net
Wed Mar 5 20:45:42 UTC 2008


Jean-Christophe Deschamps wrote:
> Dear group,
>
> I'm a newbie here, so please bear with me.
>
> I'm about to buy a FEI 5680A Rubidium frequency standard off 
> ebay.  From what I've gathered, these units were used in the telco 
> industry for about 10 years, but are still useable for my needs.  I 
> wish to have a reasonably good frequency standard for calibrating test 
> equipment (scope calibrators, function generators, etc), say every 6 
> months or once a year.  For such use I really don't need extreme 
> stability/accuracy.  Only hope is that the physics part isn't 
> completely dead.
>
> These units typically only produce a 1pps signal, but have the capacity 
> to produce the classical 10 MHz sine wave.
>
> I've found a number of documents explaining how to have the 10 MHz 
> produced by these versions.  Two of them give consistent informations 
> and seem to be sufficiently documented to be of real value.
>
> Drop me a mail at jcd at q-e-d.org if you feel posting the files could 
> help someone.  I don't know how to post files so that readers of this 
> list can access them. Anyway, I'll postpone distributing the files at 
> large until I check by myself their contents is useful.
>
> Feedback welcome!
>
>   
It seems there were many versions of the 5680A that look about the same 
but are very different. Some run on just +15 V and some need that and 
+5V. I suspect there are other voltage options too. Some are adjustable 
in frequency with software commands or a C-field screw.

I bought one in early 2005. I figured out by reverse engineering that it 
needed both +15 and +5 V. It provides both 10 MHz and 1pps outputs on 
the D-connector. I never found a way to get it to respond to any serial 
commands, although it has rs-232 interface chips and the signals were 
propagating inside. I never found any way to adjust the frequency on 
this one.

Other people clearly have units that run on just +15V and do respond to 
serial commands to set the frequency. One person reported they were able 
to adjust the frequency on theirs with a screw setting.

So it is hard to say what you may get. You may want to search the 
time-nuts archives, particularly in 2005.





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