[time-nuts] Three-cornered hat on timelab?
magnus at rubidium.se
Sat Apr 29 07:45:02 EDT 2017
On 04/27/2017 06:48 PM, Bob Stewart wrote:
> Hi Magnus,
> Try as I might, the weather and the local power company had other ideas
> about my long term capture. I'm running everything but the 5370 from a
> UPS. I guess I'm going to have to get batteries for my other UPS and
> run the 5370 from that. A one second power loss was all it took to stop
> the test.
Annoying, but you got some good values never the less.
> Anyway, I did manage to get 376,238 points of data. The data is
> captured on a 5370A. The external clock input and the STOP channel are
> fed by the 10MHz from my PRS-45A. The START channel is fed by the 10MHz
> from one of my GPSDOs. The EXT channel is fed by the 1PPS from another
> of my GPSDO units. "EXT ARM" is enabled. So, essentially, at every
> 1PPS pulse, the phase difference between the two 10MHz feeds is captured.
OK, this seems like a good setup.
> I've attached a screenshot of the phase plot which can also be found here:
> I've also made the timelab file (compressed by 7z) available here:
Thank you for providing the data, I downloaded it so I can play around
with it, which I naturally did. :)
> So, back to my question: Where are the large ionospheric phase moves?
> This question has been causing me doubt since I started on this
> project. Or don't I still have enough data collected for this to happen?
Your data seems to be more affected by constellation shifts, as the
period of about 43080 s seems to be a period of the constellation.
You either have averaged out to a somewhat incorrect position of your
antenna or you have sub-optimal position of your antenna.
It gives you a peak-to-peak amplitude of about 10 ns or so.
The ionospheric errors has a period of 86400s, so to get a clear
separation of these would take more data. However, playing around with
the data in TimeLab allowed me to filter out some of the other systematics.
The day-to-day variations is noticeable. I wonder how much of that is
thermal though. The building variations was filtered out in the process.
One has to identify a number of these potential disturbances, estimate
their size in order to more clearly see other things. TimeLab has a
notch filter to notch out a particular frequency. It would be nice if an
alternative approach would be to give the notch a period.
One has to recall that even and odd harmonics to a disturbance frequency
can be there, as it is not always a pure sine disturbance.
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