[time-nuts] Allan deviation vs standard deviation

[SAIDJACK at aol.com]

Hi Rick,
 
In my experience the 53132 is not good for ADEV measurements below 100s. It 
 is just way too noisy. 
 
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).
 
You can capture the serial output of the 53132A and use Ulrich Bangerts'  
free Plotter utility to calculate SD and ADEV from that dataset. Very easy to 
 do, but as I said not useful for anything but mediocre oscillators due to  
the high internal noise of that counter.
 
One more tip: if you measure a 10MHz signal, then use a divide by 2 (flip  
flop etc) to get to 5MHz, and scale the measurement by 2x using the Math  
setting, this will give you one more significant digit on the 53132A due to a  
weird internal limitation of that counter.
 
bye,
Said
 
 
 
 
In a message dated 9/7/2011 16:17:18 Pacific Daylight Time,  
richard at karlquist.com writes:

I was  playing with an Agilent 53132 counter, and noticed that
it measures  "standard deviation" but doesn't seem to offer
what everyone really wants,  ie, Allan deviation.  According
to the textbooks, standard deviation  won't work for oscillators
because the mean is not fixed and the deviation  goes to infinity.
However, I tried it anyway on a high quality oscillator  for
100 measurements of one second each (N=100) and it seemed  to
basically work, giving 2E-11 for the deviation.  The drift
over  100 seconds may be small enough that the mean didn't
move  significantly.  I have a 53230 on order that does
actually measure  Allan deviation, but am trying to get some
work done in the mean time with  what I currently have.

Can anyone comment on the relationship between  the two
types of measurements in the lab?  (We know how they
differ  mathematically, but what is the practical  implication).

Rick