[time-nuts] Allan Deviation Calulations

[Bruce Griffiths]

mike cook wrote:
> Le 22/09/2011 12:35, Martyn Smith a écrit :
>> Hello,
>>
>> I'm trying to measure the Allan Deviation of an amplifier and need 
>> help with
>> the maths.
>>
>> My measurement process uses the SR620 in time interval mode and I 
>> make one
>> measurement per second for about a day.
>>
>> I then use Ulrichs excellent plotter to calculate the Allan Deviation.
>>
>> The Allan Dev floor noise of the SR620 (without my amplifier) is as 
>> follows.
>>
>> 9.91E-13 (1 second)
>> 1.59 E-13 (10 sec)
>> 3.00 E-14 (100 sec)
>>
>> I then add my amplifier into the measurement process.  I get the 
>> following
>> Allan Dev results
>>
>> 1.09E-12 (1 sec)
>> 2.48E-13 (10 sec)
>> 4.32E-14 (100 sec).
>>
>> So the 1 sec Allan dev with my amp included, has gone up by 9.9E-14 
>> for the
>> 1 sec measurement.
>>
>> How to I calculate the actual Allan Dev of my amp for the 1 sec period?
>>
>> Best Regards
>>
> I have always thought of a noise floor as the lower limit to which you 
> can trust your measurement. Measurements below the floor can be 
> statistically derived IIRC, but calculating the Allan deviation of it 
> makes no sense to me.  As your measurements are all above it , you can 
> trust them.
>
Since the noise floor isnt provided your conclusion itself isnt sustainable.
>
>> Martyn
>>
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>
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