[time-nuts] HP53132A vs SR625

Rick Karlquist richard at karlquist.com
Sat Mar 16 14:57:30 EDT 2013

>>1) I paid quite a bit of money and I had it "calibrated" and fixed by
>> SRS,
>>and it still exhibits a significant frequency offset with a "perfect"
>>reference  and "perfect" DUT!!!
>>SRS says a small frequency error is "normal", well that prevents me from
>>using the unit as a frequency counter, for me it's only useful as a
>> relative
>>display frequency counter. HP doesn't have such a frequency error, so no
>>worries there.

I worked with the guy who designed the HP53132A.  He would
never tolerate as "normal" a so-called small error.  The term
"frequency counter" brings to mind something that digitally counts
zero crossings and should never have an error.  First of all, even
if that is all you do, it is still possible to screw it up.
Secondly, "counters" have relied on analog interpolation even going
back to the HP524 circa 1950.  There is no theoretical basis of having zero
error in this case, but the idea is that you display the number of
digits that are commensurate with the worst case accuracy of your
interpolator.  Again, my colleague who designed the interpolator
did very high quality work.  I am pleased to learn that our stuff
is better than the stuff from the company up the road.

Rick Karlquist N6RK
HP Santa Clara Division 1979-1998
(still working for Agilent!)

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