[time-nuts] Measuring ADEV with a PM6681 or CNT-81

Magnus Danielson magnus at rubidium.dyndns.org
Fri Oct 24 09:20:02 UTC 2008

Heinzmann, Stefan (ALC NetworX GmbH) wrote:
> Thanks, Tom!
> Apart from the specifics with TimeView, how does one go about measuring ADEV with a counter that does have a dead-time? Are there
> tricks that can be played, either with a special measurement setup or with some data postprocessing? Or with two counters that
> are somehow made to cooperate?

Consider when you compare two PPS signals. If you counter has a dead 
time of say 100 ms then it is only a certain phase relationship which 
causes the counter to miss a count if you have a counter requiring 
channel A to trigger prior to channel B (or vice versa). If you have +/- 
TI mode then channel A or B can act as a start, and then the other 
channel acts like stop. Then you can hide the dead period as it 
dynamically shifts over.

The trouble with dead time is much more annoying when you need to count 
the cycles of the signals. The PPS case does that counting without 
having dead-time, so we only need to handle the wrappings of those counters.

> Sorry if I'm asking the obvious, you can see that I'm a greenhorn. ;-)

It is a fair question.

Besides, if Tom sent the question to Staffan, then it will be a little 
while since he is on vacation.

Björn has a PM6681, he can actually TRY IT. :)


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