[time-nuts] Reference oscillator requirements when measuring ADEV ?

[Mark Spencer]

I'm curious in knowing if there are any rules of thumb as to how much better a 
reference oscillator needs to be than the device under test when measuring ADEV 
?
 
To provide a bit of context to my question I'm using a HP 5370B to repeatedly 
measure the time interval between the 10 Mhz signals from a FTS 1050 and 
rubidium oscillator.   

 
Having compared the FTS 1050 to another OCXO in the past I'm confident that it 
is meeting or exceeding it's spec of an ADEV of 1X10-12 or better at tau's of 
say 100 thru 1000 seconds.   I'm also confident that at tau's of 100 seconds or 
more the noise introduced by the 5370B is less than 1x10-12.   
 
The underlying question that I have is how much confidence could I put in 
measurements that show the rubidium of having an ADEV of say less than 2.0X10-12 
at a tau of 100 sec ?   


This is just for a hobby (: and I'm not looking for any degree of certainty but 
I'm curious in understanding how accurate the measurements might be and if 
changes in the measurements might not be caused by changes in the device under 
test.  
 
Thanks in advance for any replies.
 
Regards
Mark Spencer