[time-nuts] Three-cornered hat on timelab?
j99harman at gmail.com
Sat Apr 29 10:14:58 EDT 2017
On Thu, Apr 27, 2017 at 12:48 PM, Bob Stewart <bob at evoria.net> wrote:
> 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?
Bob, my test setup is a good deal simpler than yours, but attached is a
plot that I think shows the variations you are looking for quite clearly.
This is data from my homebrew GPSDO, which uses an Adafruit non-timing GPS
module and a run-of-the-mill surplus OCXO. The plot records the phase
comparator output over a period of about 1 week. The time constant of the
PLL is 1024 seconds and it is plotting the 5-minute average TIC values.
The full horizontal scale is 24 hours.
The vertical scale shows the data from several days with the traces for
successive days offset upwards by the equivalent of 40 nsec.
As you can see there is pretty good correlation of the phase error from day
to day and the wiggles migrate to the left a little, corresponding to the
23:56:04 siderial repeat time of the GPS constellation.This is with a
pretty good antenna location, under a shingle roof in the attic. I
calculate the day-to-day correlation at about 0.8.
Making the time constant larger increases the variations somewhat, because
the loop does not adjust as much, and they definitely get worse if I use a
less optimal antenna location.
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