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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