[time-nuts] Three-cornered hat on timelab?

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 30 02:13:55 EDT 2017


Errors aligning up due to sidreal time is most likely due to the 
multipath errors and repeated upload shifts.

Solar shifts would align up on 24 h basis.

The filtering of the time-constant is expected.


On 04/29/2017 04:14 PM, Jim Harman wrote:
> 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
> 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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