[time-nuts] ADEV vs MDEV

Pete Rawson peterawson at earthlink.net
Sun Feb 7 00:01:50 UTC 2010



The paper you provided the last link for is excellent.
I haven't seen it before & it provides a marvelous 
explanation of the various stability tools.

The specs on the CNT81 don't reveal that the 50ps
single shot TI capability is what the built-in display
shows. The GPIB data provides 25ps resolution,
which is the internal data.

My measurement setup begins with a Wenzel
Sprinter OCXO @ 100MHz. This feeds an Analog
Devices AD9513 evaluation board providing 2
10MHz outputs (norm & complement). One of 
these outputs clocks a 74HC4059 in divide by
1E4 mode. That 1KHz pulse starts the CNT81.
The other 10MHz output stops the CNT81.
The TI measurement is paced at 4ms delay.
The CNT81 reference is supplied by a Tbolt
10MHz output.

The resulting series of TI measurements are
nominally 77ns, taken every 5ms, back-to-back.

I use "Plotter" to analyze and plot the ADEV &
MDEV results (Thank you to Ulrich for such a
fine tool). The MDEV line crosses the 1E-13
level at, or very near, 10s. As expected, the MDEV
slope is -3/2 on the log-log plot vs. the ADEV
slope of -1.

I would be happy to send a typical data file to
you, if it would be of interest.


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