[time-nuts] Allan deviation vs standard deviation

Rick Karlquist richard at karlquist.com
Thu Sep 8 00:53:32 UTC 2011

SAIDJACK at aol.com wrote:
> Hi Rick,
> In my experience the 53132 is not good for ADEV measurements below 100s.
> It
>  is just way too noisy.

Now I vaguely remember:  the buffer circuit for the external reference
is a poor design, because the designers didn't know any better and
didn't ask for help.  (I knew the designers).  So even though I am using
the 10811 inside of an 8662A as an external reference, the 53132
won't get the full performance of it.  I hope the 53230 is better.
The counters are designed and made in Asia now, so I can't
exercise the proverbial HP "next bench" paradigm very well when
the bench is on another continent.

> You can try longer measurement gate and averaging times, but theoretically
> the SD value should be similar for 100s or 1000s SD measurements if what
> you are  measuring is actually the internal noise of the counter (this is
> what
> I  suspect).

I think you're right.  I'm measuring a 10811 on the bench vs
the 10811 in 8662.  Interestingly, if I feed the 8662's 10 MHz
output to both the external reference and the front panel at the
same time, the display reads exactly 10 MHz most of the time,
or occasionally drops by 1 count (1 part in 12).  This would
make it seem like the buffer inside is OK.


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