[time-nuts] Trimble Thunderbolt no longer determines the correct date
Tom Van Baak
tvb at LeapSecond.com
Sun Jul 30 10:18:34 EDT 2017
> I was running Tboltmon as the rollover occurred and did not see any phase shift.
I'm pleased you saw no phase shift at all. Did you happen to have a TBoltmon log running?
> Maybe your phase offset was due to your Tbolt being in survey mode and its apparent position shifted .
The particular TBolt I used for the screen capture was powered up too soon before GPS midnight for the survey to complete. So I just entered the coordinates manually before the photo-op.
But if you look at the two images again, the phase shift may be due to a change in DAC value. My theory at this point is that the DAC voltage calculation includes at least one component based on slope; and slope implies elapsed time interval. A calculation like that would be upset if the underlying time frame changes by -1023 weeks instead of +1 week, or -7168 days instead of +1 day, etc. Or maybe the TBolt reset on rollover and went back to a previously saved DAC value. I don't know. But for those of you making your own GPSDO, keep subtle details like this in mind.
The duration of the recovery depends on the time constant. Notice that Mark uses a 500 s time constant and I used the default (100 s), so my TBolt recovered much quicker than his. I'll have more info as I sift through several TBolt's.
----- Original Message -----
From: "Mike Cook" <michael.cook at sfr.fr>
To: "Tom Van Baak" <tvb at leapsecond.com>; "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Saturday, July 29, 2017 11:47 PM
Subject: Re: [time-nuts] Trimble Thunderbolt no longer determines the correct date
I was running Tboltmon as the rollover occurred and did not see any phase shift. Old type Tbolt firmware 3.0
Maybe your phase offset was due to your Tbolt being in survey mode and its apparent position shifted .
> Le 30 juil. 2017 à 02:16, Tom Van Baak <tvb at LeapSecond.com> a écrit :
> Caught it. Some Trimble Thunderbolt TBoltmon.exe screen shots attached:
> GPS WN 1959 TOW 604799 (July 29, 2017 23:59:41) advanced to
> GPS WN 936 TOW 0 (December 13, 1997) instead of
> GPS WN 1960 TOW 0 (July 29, 2017 23:59:42).
> 1960 - 936 is 1024 weeks, as advertised for this version of the TBolt GPSDO. Note this happened at 23:59:42 UTC as expected (that's GPS midnight - 18 UTC leap seconds). I did not expect the reported 2.75 us 1PPS phase change and will look into that.
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