[time-nuts] Best test setup?

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Dec 29 18:55:01 UTC 2009


Skip Withrow wrote:
>
> Hello time-nuts,
> I'm looking for the group expertise to tell me what would be the best 
> test setup for looking at ADEV of several oscillators.
> I have severa crystal, rubidium, and GPSDO oscillators that I would 
> like to characterize.  I have a 5370B and cesium that has 1, 5, and 10 
> MHz output.  The question is what is the best configuration of 
> internal/external oscillator, start input, and stop input of the 5370B 
> (and do I use an external 1pps trigger)?
> Then there is the issue of whether to use the cesium as the reference 
> in all cases.  Seems the GPSDO would have better long term stability 
> for very long tau.  Any insight appreciated.
> Regards,
> Skip Withrow
>
>
One setup that works well is to divide down one of the oscillators being 
compared to 1Hz (or 10Hz, 100Hz) and use this to arm the 5370B.
Use the input signal for the divider to Start the 5370B and use the 
other source to stop the 5370B.
This setup minimises the effect of divider jitter so that the technology 
employed in the divider isnt critical.
Then one has to unwrap the phase of the measured time intervals, a 
fairly straightforward task.
This method also ensures that the 5370B time base accuracy isn't 
critical as the 5370B only measures time intervals of around 1 period of 
the STOP input frequency.
For quiet sources the measurement noise of the 5370B will dominate for 
tau less than 100sec or so (depends on the source ADEV vs tau).

Bruce




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