I don't have the data logging set up yet, but I can combine the TI measurement with the built-in stats calculation on the 53131A.
Not sure I have this right - 53131A is not known for its intuitive UI. I set it up for "TI 1 to 2" measurement, then enabled Statistics with 1000 samples and ran a single stats cycle. Both channels have 50 ohm termination, AC coupling, auto trigger levels.
(All values in microseconds unless otherwise noted)
Lucent to Huawei - StdDev 0.000590; Mean 0.091113; Max 0.0923; Min 0.0898 -> (max - min) = 2.5 ns
Lucent to Trimble - StdDev 0.000355; Mean 0.047302; Max 0.0488; Min 0.0463 -> (max-min) = 2.5 ns
Lucent to BG7TBL - StdDev 0.000356; Mean 0.095016; Max 0.0958; Min 0.0943 -> (max-min) = 1.5 ns
Trimble to Huawei - StdDev 0.000685; Mean 0.050237; Max 0.0523; Min 0.0488 -> (max-min) = 3.5 ns
Trimble to BG7TBL - StdDev 0.000615; Mean 0.050347; Max 0.0523; Min 0.0493 -> (max-min) = 3.0 ns
Huwaei to BG7TBL - StdDev 0.000952; Mean 0.018382; Max 0.0213; Min 0.0163 -> (max-min) = 5.0 ns
I might have upset things a bit by jostling the GPSDO enclosures. It's hard to plug/unplug BNCs on these things. I will let them sit for awhile and repeat one of the measurements to see how much it changes. Might also make sense to do a longer sample run - maybe 10,000 samples.
(edit) More samples on Huawei to BG7TGBL - StdDev 0.010116; Mean 0.0355101; Max 0.0523; Min 0.0203 -> (max-min) = 32 ns
This is useful information. It shows that all the units appear to be working properly. For most users, any of them would provide excellent service.
Now, can we answer the question: Which one of these units is the best? Moto, in the unlikely case that you haven't figured it out yet, I'm playing to the audience here!
The mean, max, and min values are arbitrary so they aren't useful. Every test will give different values.
The Std. Dev. and Max-Min values are very useful. You would expect those values to be similar (but not equal) from one test to another. The two lowest Std. Dev. values both include the Lucent which suggests that it's the best one. The Max-Min values are also at the low end of the scale. The Trimble measurements are in the middle. Huawei comes next. But the BG7TBL measurements are both the best and worst of the pack!
No, nothing's wrong. These results aren't surprising. GPS signals have jitter, so anytime you take a snapshot you could get a really good result or a not-so-good result. Your edit clearly shows the affect of a not-so-good snapshot. That one justifies the term 'outlier'. We pretend that those measurements never happened. Seriously, that's allowed! Something hiccupped and the data is trash so you discard it.
To get some useful results out of these measurements, you have to take multiple data runs and compare the results to determine what typical results are.
Regarding the data logging, I urge you to get that going. Timelab handles both the data collection and analysis. All you have to do is plug in the cable! Well, okay, you have to configure the serial port. And I guess you have to figure out which cable wiring you need. But you can handle that!
Logging the data will move you out of the 'snapshot' business. You'll be able to see how the units perform over time and your comparisons will be more consistent. You should be able to confirm the frequency error of the BG7TBL unit - unless he's come out with a new firmware version that fixes the problem. That would be interesting news!
If you look back at
this message, it shows some of the things that Timelab can tell you about these units. Yeah yeah, I know tl;dr, and even when you try and read it your eyes glaze over. What can I say? If you were trying to measure the diameter of a metal shaft, would you use a plastic ruler or learn how to use a micrometer?
Ed
P.S. Do I dare mention that the best way to evaluate a GPSDO is to compare it to a local standard like a Rubidium oscillator?