[time-nuts] Three-cornered hat on timelab?
magnus at rubidium.se
Sat Apr 29 10:52:54 EDT 2017
For that receiver, you have a pretty good result.
If you haven't moved your antenna, the average result should be fine.
However, with a cesium around you can experiment with minor adjustments
of position. Best would be to build carrier phase pseudo-range
measurements and compare with the time-difference to see if there is a
correlation and then fine-tune that way. I don't recall what you get out
of the LEA-6T.
You sure has some outdoor temperature variations right now.
It would be interesting to do an outdoor and indoor temperature log and
try to see the correlation there.
On 04/29/2017 04:35 PM, Bob Stewart wrote:
> Hi Magnus,
> OK, a couple of things about my location. I'm in West Houston, and it's
> not summer yet, so there's a lot of variation in temperature from day to
> day. Some nights it's in the 40sF and some nights it's in the high 70s
> or low 80sF. Lots of variation in the days, as well. My antenna is not
> optimal, at all. The best I could do was to remove the dish from an
> unused DishTV antenna and install my GPS antenna on top of the little
> mast they use. It's about the best I can do. In fact, it's better than
> I expected.
> The receiver is a LEA-6T that was put through a 24 hour survey and the
> position was saved in flash memory. However, there have been lots of
> power cycles since that survey. Whether or not that affects the result,
> I don't know.
> Still, the point of the test was to understand why I'm not getting these
> large phase swings. And I think Bob Camp's explanation was good. Maybe
> in another 5 years the sunspots will be back up and I can see the
> comparison to now.
> *From:* Magnus Danielson <magnus at rubidium.se>
> *To:* Bob Stewart <bob at evoria.net>; Discussion of Precise Time and
> Frequency Measurement <time-nuts at febo.com>
> *Cc:* magnus at rubidium.se
> *Sent:* Saturday, April 29, 2017 6:45 AM
> *Subject:* Re: [time-nuts] Three-cornered hat on timelab?
> Hi Bob,
> 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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