[time-nuts] Cross-Correlation Results

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Aug 4 21:02:25 UTC 2012

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.


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