[time-nuts] removing sidereal correlation
magnus at rubidium.dyndns.org
Sun Apr 30 14:08:06 EDT 2017
Upload rate could be one. There is some systematics due to jumps from
the old to new estimation. I think I recall a 2 h upload rate, but no
guarantee for that number.
On 04/30/2017 06:32 PM, Eric Scace wrote:
> What other patterns, if any, are uncovered if one removes a smoothed sidereal variation?
> — Eric
>> Begin forwarded message:
>> From: Jim Harman <j99harman at gmail.com>
>> Subject: Re: [time-nuts] Three-cornered hat on timelab?
>> Date: 2017 Apr 29 Sat at 10:14:58 EDT
>> To: Bob Stewart <bob at evoria.net>, Discussion of precise time and frequency measurement <time-nuts at febo.com>
>> Reply-To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>> 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.
>> --Jim Harman
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