Hi
> On Jan 25, 2015, at 10:59 AM, Didier Juges <shali...@gmail.com> wrote: > > "This operation is very typical of all of the cell site GPSDO’s. The only > part that is unique to the TBolt is the ability to fiddle the loop > characteristics a bit." > > And the fact that the GPS's CPU clock is derived from the 10MHz and > therefore aligned to the PPS so there is no hanging bridge and sawtooth > correction is not required. > > I am not aware of any other GPSDO implementing that scheme, which is very > elegant in its simplicity. It is indeed an elegant solution. Based on looking at 1 pps outputs on a group of them over a year or more, It’s actual impact on the control loop function is pretty minor compared to a properly executed sawtooth correction process. It would have a significant advantage if compared to a GPSDO that does not use sawtooth correction. Bob > > Didier KO4BB > > > On Sat, Jan 24, 2015 at 8:18 AM, Bob Camp <kb...@n1k.org> wrote: > >> Hi >> >> Maybe a bit more information, much of it applies to all GPSDO’s : >> >> The TBolt first goes through a process to get the OCXO roughly on >> frequency and to get the PPS approximately aligned. That process is not >> impacted by the time constant and damping. The OCXO goes a bit crazy during >> this process. >> >> It then starts the phase lock process with a short time constant. As the >> OCXO settles in, it will step out to a progressively longer time constant. >> It does this based on it’s internal estimates of lock quality. Unless you >> are already at maximum time constant and have a good internal estimate, >> changing the time constant has no immediate impact. On most GPSDO’s and >> with most OCXO’s under most conditions, the step out process takes days or >> weeks. >> >> The damping number does impact the performance in the maximum time >> constant mode. It may be scaled as the time constant is changed. >> >> There does appear to be a D in the TBolt loop. For what ever reason, >> that’s not a changeable value. The D does scale with the time constant. >> >> When in lock mode, the TBolt is a PLL and not a FLL. As the “phase in” >> (the pps from the gps) moves, the frequency of the OCXO will change to keep >> the “phase out” (PPS output) aligned. As the unit is running, it keeps >> track of the average DAC value that puts the OCXO on frequency. Since it’s >> a PLL, that number may or may not be the last instantaneous value of the >> DAC when it goes into holdover. Since it’s running a PLL, the PPS output >> will indeed be the best value, so no correction is needed there when it >> goes into holdover (not quite true, but that is the assumption made). >> >> This operation is very typical of all of the cell site GPSDO’s. The only >> part that is unique to the TBolt is the ability to fiddle the loop >> characteristics a bit. >> >> Bob >> >>> On Jan 23, 2015, at 10:58 PM, Skip Withrow <skip.with...@gmail.com> >> wrote: >>> >>> Hello Nuts, >>> I have been playing a bit tuning a Thunderbolt with Lady Heather and now >>> have more questions than answers. The collective time-nut brain would be >>> appreciated. >>> >>> 1. Using the '&' command I can change the damping and time constant in >> LH. >>> Are these values immediately transferred to the TB? >>> >>> 2. Do I have to use the LH 'e' command to permenantly save new damping >> and >>> time constant values to the TB? >>> >>> 3. After using the '&' and 'e' command the lock-in behaviour of the TB >> does >>> not seem to change. Is this normal behaviour? Is one set of values used >>> when locking and the adjusted values used once it is phase locked? >>> >>> 4.Is there some way to read out the values stored in the TB? When I use >>> the 'e' command on the TB, change values in LH, then restart LH and the >> TB >>> I see the last values given to LH, and not what I thought was saved with >>> the 'e' command. >>> >>> 5. If the TB is placed in hold mode and the DAC set to 0.0 volts it >>> actually goes to 0.2 volts (min is at -5, max is at +5, and iv is 0.0 >> which >>> it actually starts at on power up). Anyone know why? >>> >>> Thanks in advance for any guidance! >>> Regards, >>> Skip Withrow >>> _______________________________________________ >>> 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. >> >> _______________________________________________ >> 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. >> > _______________________________________________ > 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. _______________________________________________ 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.