We have been following the Tbolt power discussions but what I am missing is the main problem with Tbolts. All the power work will not improve the frequency performance of the unit because the frequency is constantly changed to correct time. Tbolt is an excellent time device but not good for frequency reference past 1E-10. I noticed it when I bought it and compared it with my Tracor 527E on the needle and ever since used an Austron 2110 with a digital 100 sec. loop for clean up. My Swiss partner Juerg has relied on an OSA F3 for Tbolt clean up but continuous bad results on our work resulted in a detailed analysis using a HP53132A counter and M100, FTS44060, two OSA8600's and one of the best FE405's. The rsult is that the OSA F3 does not clean up the Tbolt and we see +-4E-11 changes and old data shows even some +-8 E-11 excursions. With the popularity of the Tbolt an analog or digital clean up loop would make sense. We are working on both, the analog because I saw similar behavior on the FE5680 and FE5650, we did a GPSDO but do not plan on using those Rb's but focus on M100 and FRK. The collective expertise of time nuts could make a significant contribution For power in critical applications we use the excellent work from Bern Kaa a friend for the last twenty years and well known because of his published work in the European HAM community Bert Kehren

On Thu, September 1, 2016 11:54 am, Bert Kehren via time-nuts wrote: > All the power work will not improve the frequency performance > of the unit because the frequency is constantly changed > to correct time. Can't you control that to a large extent with the damping and time constant parameters? -- Chris Caudle

Hi Bert, > because the frequency is constantly changed to correct time. A simple answer: you may have a bad TBolt. Was it part of the TAPR group buy, or did you buy it from eBay/China? If TAPR, you get a free replacement. Contact me off-list. > Tbolt is an excellent time device but not good for frequency reference past 1E-10. No, again it sounds like you have a bad TBolt. Or something is wrong (antenna? reception? time constant? environment? China resoldered parts?). I appreciate that Juerg did lots of testing -- do you happen to have his ADEV plot? I'm willing to help you debug this. (1) Attached is the ADEV of 8 random TBolts that I tested recently. How does this compare to yours? You can see mine are all under 2e-12 at 1 s and under 4e-12 at 100 s. On a bad day during holdover it might climb to 1e-11 at 1000 s but when locked GPS disciplining takes over and keeps it down to 2 or 3e-12. (2) For locked vs. unlocked TBolt ADEV, see http://www.leapsecond.com/pages/gpsdo/ (3) Also attached is a frequency plot showing the typical noise and wander, down at the 1e-11 level. How does this compare with yours? Your claim of 1e-10 is order(s) of magnitude worse than the TBolts that I see. Something is wrong. /tvb ----- Original Message ----- From: "Bert Kehren via time-nuts" <time-nuts@febo.com> To: <time-nuts@febo.com> Sent: Thursday, September 01, 2016 9:54 AM Subject: [time-nuts] Tbolt issues > We have been following the Tbolt power discussions but what I am missing is > the main problem with Tbolts. All the power work will not improve the > frequency performance of the unit because the frequency is constantly changed > to correct time. Tbolt is an excellent time device but not good for > frequency reference past 1E-10. I noticed it when I bought it and compared it with > my Tracor 527E on the needle and ever since used an Austron 2110 with a > digital 100 sec. loop for clean up. My Swiss partner Juerg has relied on an > OSA F3 for Tbolt clean up but continuous bad results on our work resulted in > a detailed analysis using a HP53132A counter and M100, FTS44060, two > OSA8600's and one of the best FE405's. The rsult is that the OSA F3 does not > clean up the Tbolt and we see +-4E-11 changes and old data shows even some +-8 > E-11 excursions. With the popularity of the Tbolt an analog or digital > clean up loop would make sense. We are working on both, the analog because I > saw similar behavior on the FE5680 and FE5650, we did a GPSDO but do not plan > on using those Rb's but focus on M100 and FRK. > The collective expertise of time nuts could make a significant contribution > For power in critical applications we use the excellent work from Bern Kaa > a friend for the last twenty years and well known because of his published > work in the European HAM community > Bert Kehren

Tom wrote: > No, again it sounds like you have a bad TBolt. Or something is wrong (antenna? reception? time constant? environment? China resoldered parts?). I appreciate that Juerg did lots of testing -- do you happen to have his ADEV plot? > > Your claim of 1e-10 is order(s) of magnitude worse than the TBolts that I see. Something is wrong. I second that (not that any further evidence is necessary following Tom's comprehensive response). Additionally, as far as I know, the units Tom was testing would have had the default tuning parameters (Tom, please comment). Most Tbolts I've seen can be tuned for much better performance than this at tau > 100 seconds, if they are equipped with a 37265 OCXO. Note that the Tbolt has tuning parameters that limit how far the frequency is allowed to wander to adjust the PPS phase -- if Bert's unit(s) have these parameters set to allow very fast PPS recovery, that could well cause the behavior he describes. You should also check all of the other tuning parameters to see if there are errors in the settings. However, rather than mucking about in the myriad tuning settings starting where they are now, I recommend doing a full factory reset to get all parameters back to the original settings. Then (after several weeks of undisturbed running), compare ADEV performance with Tom's graphs. Best regards, Charles

Hi I think one issue here is that ADEV is being used by one “lab" and absolute frequency is being used by the other. They very much are *not* the same thing. There isn’t even a really simple way to convert one to the other. There will always be a big delta between those two measures. For absolute frequency you will also need some sort of confidence number (99 % or some such thing). The details of why all this happens are the mainstay of the 1960’s (and early 70’s) papers on ADEV. Bob > On Sep 1, 2016, at 3:11 PM, Tom Van Baak <tvb@LeapSecond.com> wrote: > > Hi Bert, > >> because the frequency is constantly changed to correct time. > > A simple answer: you may have a bad TBolt. Was it part of the TAPR group buy, or did you buy it from eBay/China? If TAPR, you get a free replacement. Contact me off-list. > >> Tbolt is an excellent time device but not good for frequency reference past 1E-10. > > No, again it sounds like you have a bad TBolt. Or something is wrong (antenna? reception? time constant? environment? China resoldered parts?). I appreciate that Juerg did lots of testing -- do you happen to have his ADEV plot? > > I'm willing to help you debug this. > > (1) Attached is the ADEV of 8 random TBolts that I tested recently. How does this compare to yours? You can see mine are all under 2e-12 at 1 s and under 4e-12 at 100 s. On a bad day during holdover it might climb to 1e-11 at 1000 s but when locked GPS disciplining takes over and keeps it down to 2 or 3e-12. > > (2) For locked vs. unlocked TBolt ADEV, see http://www.leapsecond.com/pages/gpsdo/ > > (3) Also attached is a frequency plot showing the typical noise and wander, down at the 1e-11 level. How does this compare with yours? > > Your claim of 1e-10 is order(s) of magnitude worse than the TBolts that I see. Something is wrong. > > /tvb > > ----- Original Message ----- > From: "Bert Kehren via time-nuts" <time-nuts@febo.com> > To: <time-nuts@febo.com> > Sent: Thursday, September 01, 2016 9:54 AM > Subject: [time-nuts] Tbolt issues > > >> We have been following the Tbolt power discussions but what I am missing is >> the main problem with Tbolts. All the power work will not improve the >> frequency performance of the unit because the frequency is constantly changed >> to correct time. Tbolt is an excellent time device but not good for >> frequency reference past 1E-10. I noticed it when I bought it and compared it with >> my Tracor 527E on the needle and ever since used an Austron 2110 with a >> digital 100 sec. loop for clean up. My Swiss partner Juerg has relied on an >> OSA F3 for Tbolt clean up but continuous bad results on our work resulted in >> a detailed analysis using a HP53132A counter and M100, FTS44060, two >> OSA8600's and one of the best FE405's. The rsult is that the OSA F3 does not >> clean up the Tbolt and we see +-4E-11 changes and old data shows even some +-8 >> E-11 excursions. With the popularity of the Tbolt an analog or digital >> clean up loop would make sense. We are working on both, the analog because I >> saw similar behavior on the FE5680 and FE5650, we did a GPSDO but do not plan >> on using those Rb's but focus on M100 and FRK. >> The collective expertise of time nuts could make a significant contribution >> For power in critical applications we use the excellent work from Bern Kaa >> a friend for the last twenty years and well known because of his published >> work in the European HAM community >> Bert Kehren > <TBolt8-1.gif><TBolt8-2.gif>_______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.