[time-nuts] HP10811 vs 00105 OCXO

Bob Camp kb8tq at n1k.org
Fri Aug 7 20:23:17 EDT 2015


Well an un-stated assumption of mine was that they all came from the same measurement system and that it 
had the same floor under all circumstances….


> On Aug 7, 2015, at 5:21 PM, John Miles <john at miles.io> wrote:
>> Hi
>> If that data is correct, then the 10811 you have is defective.
>> Bob
> Well... some of the data is reasonable for a scenario where a counter is being used to measure OCXOs.  
> Looking at the ADEV plot, I'd say the blue trace (HP105B vs 5065A) is the most questionable one if it came from a standalone TIC or frequency counter, because 7E-12 @ t=1s isn't achievable with most counters under most circumstances.  A Wavecrest box can measure at that level if it's set up _perfectly_ to take bursts of 100+ wrap-free averages within a small fraction of the t0 interval.  It might also be doable with an HP 5370A/B under similar conditions, but I'd have less confidence that the averaging isn't distorting the measurement.  So while It looks like a valid measurement of an OCXO with some minor crosstalk or other external interference, that may just be a coincidence.  
> Luciano, how was the blue trace taken?  Is this from your DMTD project?  If so, it's looking promising.
> The green and magenta traces are definitely in the right ballpark for measurements on a 5370-class counter.  At 3E-11 @ t=12s the magenta trace is optimistic but not outrageously so, while the green trace looks exactly like I'd expect for a typical 10811 measured on a 5370.  The observed noise is due entirely to the counter until about t=200s.  We see a glimpse of the 10811's typical  ADEV at about 250 seconds, just before either drift or ADEV uncertainty causes the trace to turn upwards.  A longer run would be needed to distinguish between these two situations.
> -- john, KE5FX
> Miles Design LLC
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