[time-nuts] Cross-Correlation Results

John Ackermann N8UR jra at febo.com
Sat Aug 4 19:44:56 EDT 2012


They have their own cross-correlation system; it's not highly automated but claims -190 dBc/Hz capability: http://www.wenzel.com/pdffiles1/PNTS%201000/BP-1000-CC.pdf

John


On Aug 4, 2012, at 7:31 PM, Azelio Boriani <azelio.boriani at screen.it> wrote:

> In your opinion, how the Wenzel company got the data for the ULN
> specifications?
> 
> On Sat, Aug 4, 2012 at 11:02 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz
>> wrote:
> 
>> John Ackermann N8UR wrote:
>> 
>>> Magnus inspired me to try my own cross-correlation experiment with the
>>> TimePod today.  I used two fairly normal OCXO frequency standards as the
>>> reference, and a Wenzel 5 MHz ULN as the device under test.
>>> 
>>> By doing single-reference measurements of each OCXO versus the ULN, I was
>>> able to plot their noise.  Since the ULN has performance near the noise
>>> floor of the TimePod, I could then test how well the correlation works to
>>> allow measurements below the noise of either reference.
>>> 
>>> Conclusion: it works *really* well.  Plots and a little write-up are at:
>>> http://www.febo.com/pages/cross-correlation/index.html
>>> 
>>> John
>>> 
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>>> 
>>> Even a pair of Trimble 34310T ocxos appear to work well as the dual
>> reference oscillators.
>> 
>> If one could use a pair of ocxos to drive the other pair of ADCs it should
>> be possible to evaluate the contribution of the Timepod itself to the noise
>> floor.
>> 
>> Using an interferometric technique with a Timepod allows a PN noise floor
>> of -200dBc/Hz or less to be achieved (with a test source noise floor of
>> around -175dBc/Hz or worse) when measuring the additive PN of components
>> such as amplifiers.
>> 
>> Bruce
>> 
>> 
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