[time-nuts] Timepod Phase Noise Measurements and 3 corner hat

John Miles john at miles.io
Sun Aug 30 23:12:51 EDT 2015

> On that note, did you look more closely on the NIST analysis of
> cross-correlation and a possible cancellation and thus overly optimistic
> results? Did it have any consequence on your code? What did you take
> away from it?

Yes, you can definitely get divots in the PN trace, especially in multiple-hour runs needed to reach very low noise levels.  I've seen that on occasion when making measurements with independent downconverters.  If the DUT signal experiences significant phase shift in one downconverter path relative to the other, I imagine that's a good way to provoke this behavior.  

Fortunately I haven't run into any instances of the worst-case scenario described in the Nelson paper, where the whole noise floor collapses without any exhibiting any other weird artifacts.  The phenomenon is certainly worth keeping in mind but most people are not going to run into it, especially with the Ch0 and Ch2 jumpers in place.  

-- john, KE5FX
Miles Design LLC

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