[time-nuts] Furuno GT-87

[Lars Walenius]

So the orange is the second to second timestamp difference minus 1s, or the period time measured every second minus 1s. As the period is very close to 1s the frequency difference just will be the negative value so what the graph shows is the same as eg Stable 32’s frequency data for 1s but negative. As in e.g. http://www.leapsecond.com/pages/tbolt-8d/ . Also the orange line for me more seems to be the difference between adjacent ”saw tooth correction data” + some hardware noise as the edges of the PPS is very dependent on the TCXO frequency for two successive edges.

The gray line seems to be more interesting as it is what I in Stable 32 believe is called phase data.

Would be interesting to know how Furano calculates “accuracy”.

See forward for more data from the GPS and GLONASS comparison. Don´t remember to have seen anything of that from someone else!
Thanks Lars



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Från: time-nuts <time-nuts-bounces at febo.com> för Mark Sims <holrum at hotmail.com>
Skickat: Sunday, March 18, 2018 1:43:03 AM
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Ämne: [time-nuts] Furuno GT-87

The TICC reference is a HP-5071A cesium beam oscillator with high performance tube.  The GT-87 is connected to the TICC channel B input.  The TICC is running in timestamp mode.

The orange plot is the Time Interval Error of the 1PPS signal... the difference between 1 second and the measured 1PPS.

The grey plot is the accumulated phase error for channel B.

I just finished the measurement of the GT87 running on GLONASS sats only.   The PPS span was still in the +/-4 ns range with a couple of points +/- 6 ns.   However the ADEV measurements on the 1PPS were 3 (at tau-100 secs) to 5 times higher. (at tau=10000 seconds).   I am typically tracking 5-8 GLONASS sats.

The GT87 sends an "accuracy" value.  In GLONASS only mode the GT87 reports an accuracy of 12 ns.  With GPS enabled it tends to say 5-6 ns,  but I have seen it as low as 2 ns.
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