The Conner-Winfield document is good, but it might be premature to put a lot of effort into the OCXO.
Something went a little crazy in the last 1.5 hrs of your data. It could have been a temperature change, voltage change, or just the OCXO being perverse. (They do that, you know!
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) Select that data on the phase graph and delete it. Yes, you're allowed to do that. The data doesn't reflect the true performance of the oscillator so it's okay to delete it. Just like the glitches. I'm not sure where legitimate deletions end and 'cherry-picking' begins.
Now go back to the AlDev graph and you'll find that at Tau=10K sec. your AlDev has improved by almost 10x, but you've still got those stupid oscillations! The Lpro has AlDev specs of 2.5e-11@1sec and 2.5e-12@100sec. The CFPO-4 datasheet doesn't list AlDev specs, but the phase noise specs are much better than the LPRO which suggests that the AlDev numbers will also be pretty good although the correlation between AlDev and Phase Noise is far from perfect. Since both of them should be far below the measurements you've got, it suggests that the wiggles could be related to your counter! The level where the wiggles are is similar to what I expect for the counter's noise floor. Have you measured the counter's noise floor as I described earlier with the cables and T-connector? If not, you should do so before you spend a lot of time on the CFPO.
This is the kind of analysis and detective work that often happens when you're making AlDev measurements. What makes sense? Are these results believable? Too bad to be valid - Is something wrong? Too good? Yes, that can happen too.
Setting the oscillations aside for the moment, you may already be running into the limitations of your 5335 counter. Its resolution spec of 1 ns. means an AlDev of 1e-9@1sec. You're seeing 4.4e-10@1sec. so it's better than spec. Imagine drawing a line through the straight section on the left of the AlDev graph, through the bottom of each wiggle, and on to the straight section on the right of the graph. That's what you'd see without the wiggles. The slope isn't what I expect to see, but I'm not familiar with the 5335. I've attached a picture showing noise floor measurements for my counters.*
If this is the noise floor of your counter, it doesn't mean that your counter is worthless. It does mean that you can't use it to make measurements at low values of Tau. The results will get lost below the counter's noise floor. That's a fact of life with every counter. I made lots of useful measurements and learned a lot by using my Racal Dana 1992 which has a 1 ns resolution, just like your 5335. I just accepted the fact that I probably was blind to anything below about 100 sec. As you get better and better counters, you can make measurements at lower values of Tau. If I wanted to look at an LPRO, the only counter I could use is the Wavecrest DTS-2077. The others aren't really good enough.
Ultimately, counters are not the way to go when you're trying to make measurements at insanely low AlDev values. You have to go to other measurement architectures. That's not something you should get into at this time. It'll make your brain hurt!
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Ed
* (For anyone who's paying attention, yes, there's something wrong with my 5370B. It should be much better than that!)
Edit: Forgot the picture.
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