[time-nuts] Interesting (meaningless?) measurement.

Brian Alsop alsopb at nc.rr.com
Tue Jul 23 07:28:14 EDT 2013


I acquired an HP-8657B refurbished by a well regarded individual. 
Beautiful printout of unit's performance versus the test matrix.

One thing I was interested in is how well it "locks" to an external 
source.  The previous generator I had produced 5 -10 ns random jumps 
observable on a 'scope.  I've seen none of that with the 8657B.

The next question: So how good is the lock?

The experiment was to use my HP5335A to measure time difference between 
the 8656B and the Rb source locking it.  The HP5335A was locked to the 
same Rb source.  This might be pushing the 5335A's ability to reliably 
measure time differences in the 100 ps range.

The experiment produced a standard deviation of 0.27 ns at 10 MHz for a 
couple hour run.  Each data point was a 100 sample average.  Obviously 
the results have components from both the 5335A and 8656B.  Perhaps 
another measurement could be made with the internal high stability 
oscillator in the 5335A.

There is no statistically meaningful drift in mean value with time.

Good, bad or meaningless?
Brian


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