Re: [time-nuts] Trueposition behavior
I think it would be a dead-band. David N1HAC On 3/10/20 2:41 PM, djl wrote: Is this effectively dither on the control voltage? On 2020-03-10 10:30, Skip Withrow wrote: Hello Time-Nuts, A couple of weeks ago I posted regarding some weird behavior of the Trueposition GPSDO that I was seeing. I have now been able to get back to the problem and have further results to report. I have several of these GPSDOs that are version 12.0.1 (I believe the latest is 12.1.1) and they all seem to behave the same. I have attached two Lady Heather plots. One is the GPSDO output of the control voltage, the other is the 10MHz output monitored by another NTBW GPSDO. The bumps in the control voltage are what was bothering me. It appears that the way this GPSDO operates is to let the oscillator free run until there is 50ns of accumulated time error (LH reports 'Normal' during this phase), Then it goes into control mode, you can see more noise on the DAC signal during this time plus the big spike, and yanks the phase back to zero (LH reports 'Acquiring' during this phase). The unit must model the OCXO drift as the DAC does change during the drift period. So, the longer the unit runs the longer between upsets (hopefully). These plots were taken shortly after start up, I am in the process of letting it run for a while now. BTW, the very periodic dropping and acquisition of the WAAS bird (PRN138) is still present. This behavior is a good news/bad news situation. On one hand, during the drift period the output of the GPSDO is not influenced by GPS and getting yanked around second by second (like the Thunderbolt). On the other hand, if the 50ns yank happens when you are making a measurement it kind of trashes things. I haven't tried seeing if LH can disable disciplining (for use during measurement periods). Regards, Skip Withrow ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.febo.com%2Fmailman%2Flistinfo%2Ftime-nuts_lists.febo.comdata=02%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7Cbb722bbdb01b4db9fe0308d7c522c000%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637194625354501923sdata=Bx2snhE2Wbc0Fo7MNo9kcsQ61JNeycC%2FEt90tEA657k%3Dreserved=0 and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Trueposition behavior
Is this effectively dither on the control voltage? On 2020-03-10 10:30, Skip Withrow wrote: Hello Time-Nuts, A couple of weeks ago I posted regarding some weird behavior of the Trueposition GPSDO that I was seeing. I have now been able to get back to the problem and have further results to report. I have several of these GPSDOs that are version 12.0.1 (I believe the latest is 12.1.1) and they all seem to behave the same. I have attached two Lady Heather plots. One is the GPSDO output of the control voltage, the other is the 10MHz output monitored by another NTBW GPSDO. The bumps in the control voltage are what was bothering me. It appears that the way this GPSDO operates is to let the oscillator free run until there is 50ns of accumulated time error (LH reports 'Normal' during this phase), Then it goes into control mode, you can see more noise on the DAC signal during this time plus the big spike, and yanks the phase back to zero (LH reports 'Acquiring' during this phase). The unit must model the OCXO drift as the DAC does change during the drift period. So, the longer the unit runs the longer between upsets (hopefully). These plots were taken shortly after start up, I am in the process of letting it run for a while now. BTW, the very periodic dropping and acquisition of the WAAS bird (PRN138) is still present. This behavior is a good news/bad news situation. On one hand, during the drift period the output of the GPSDO is not influenced by GPS and getting yanked around second by second (like the Thunderbolt). On the other hand, if the 50ns yank happens when you are making a measurement it kind of trashes things. I haven't tried seeing if LH can disable disciplining (for use during measurement periods). Regards, Skip Withrow ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. -- Dr. Don Latham AJ7LL PO Box 404, Frenchtown, MT, 59834 VOX: 406-626-4304 ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Trueposition behavior
Hello Time-Nuts, A couple of weeks ago I posted regarding some weird behavior of the Trueposition GPSDO that I was seeing. I have now been able to get back to the problem and have further results to report. I have several of these GPSDOs that are version 12.0.1 (I believe the latest is 12.1.1) and they all seem to behave the same. I have attached two Lady Heather plots. One is the GPSDO output of the control voltage, the other is the 10MHz output monitored by another NTBW GPSDO. The bumps in the control voltage are what was bothering me. It appears that the way this GPSDO operates is to let the oscillator free run until there is 50ns of accumulated time error (LH reports 'Normal' during this phase), Then it goes into control mode, you can see more noise on the DAC signal during this time plus the big spike, and yanks the phase back to zero (LH reports 'Acquiring' during this phase). The unit must model the OCXO drift as the DAC does change during the drift period. So, the longer the unit runs the longer between upsets (hopefully). These plots were taken shortly after start up, I am in the process of letting it run for a while now. BTW, the very periodic dropping and acquisition of the WAAS bird (PRN138) is still present. This behavior is a good news/bad news situation. On one hand, during the drift period the output of the GPSDO is not influenced by GPS and getting yanked around second by second (like the Thunderbolt). On the other hand, if the 50ns yank happens when you are making a measurement it kind of trashes things. I haven't tried seeing if LH can disable disciplining (for use during measurement periods). Regards, Skip Withrow ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.