Hi Magnus, I don't remember seeing such a report. Could you tell me where to find a copy? I've got a lot of code-space left on this PIC, so assuming I can get the hardware to cooperate, much is possible.
Bob ----------------------------------------------------------------- AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Magnus Danielson <mag...@rubidium.se> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> Cc: mag...@rubidium.se Sent: Wednesday, August 17, 2016 1:05 AM Subject: Re: [time-nuts] Holdover Bob, That is what seem to work well in commercial products, including my designs. Have you seen the RAI report on GPSDOs? I think we discussed it before, that will be a relevant reading. Not all system implements 3), and it is a bit complex, so consider it an option to add, but not necessarily always used. Sometimes you don't want to do that. Cheers, Magnus On 08/17/2016 02:08 AM, Bob Stewart wrote: > Thanks Magnus! > > These look like good guidelines. I'll see what I can come up with. > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > ------------------------------------------------------------------------ > *From:* Magnus Danielson <mag...@rubidium.dyndns.org> > *To:* time-nuts@febo.com > *Cc:* mag...@rubidium.se > *Sent:* Tuesday, August 16, 2016 6:49 PM > *Subject:* Re: [time-nuts] Holdover > > Bob, > > On 08/16/2016 11:31 PM, Bob Stewart wrote: >> Hi Attila, >> In my unit, which is a frequency standard, I chose to tell the > receiver to stop sending 1PPS pulses when it loses sync to the sats. > And since the 1PPS is no longer coming, the PLL does nothing and the DAC > doesn't change. (Let's avoid the question of aging correction for > now.) So, I'm wondering where to go and what to do if I want to get > time from my unit. Clearly I could just tell the receiver to continue > to send 1PPS pulses and sync to those - marking the time as unreliable. > When the receiver synced back up, then it would warp the time output, > the 1PPS would warp in phase, and the PLL would correct the phase error. >> >> So, that's one way, but probably not a desirable way. My interest was > in the option of using the OCXO to create the time, which clearly gives > a better option when the receiver syncs back up to the sats. Is there a > published standard for this, or is this something that everyone (except > the newbie) knows so well that it's not worth discussing? > > There is no standard, but a few basic ways to go about which seems > reasonable and used by most is: > > 1) As you go into hold-over, keep producing PPS etc > 2) As you leave hold-over, attempt to adjust the phase back. > 3) If your system been in hold-over for a longer time, say that it > reasonably deviates outside of +/- 10 us (or some other limit), alarm > and turn output off > > I have selected a somewhat more intricate setup in which you can set a > re-assignment limit, so when the phase error is outside of that limit, > you turn the output off, jumps the phase difference, and then starts to > track in from there. The reason being that at some time deviation, the > time it takes to track in the phase error is too large to be practical > so turning of and jump has less impact. > > Cheers, > Magnus > >> Bob >> ----------------------------------------------------------------- >> AE6RV.com >> >> GFS GPSDO list: >> groups.yahoo.com/neo/groups/GFS-GPSDOs/info >> >> From: Attila Kinali <att...@kinali.ch <mailto:att...@kinali.ch>> >> To: Bob Stewart <b...@evoria.net <mailto:b...@evoria.net>>; Discussion > of precise time and frequency measurement <time-nuts@febo.com > <mailto:time-nuts@febo.com>> >> Sent: Tuesday, August 16, 2016 3:46 PM >> Subject: Re: [time-nuts] Holdover >> >> On Tue, 16 Aug 2016 04:35:40 +0000 (UTC) >> Bob Stewart <b...@evoria.net <mailto:b...@evoria.net>> wrote: >> >>> It's been pointed out to me that I didn't understand the function of >>> the 1PPS of a time standard. I confess that somehow I had confused the >>> term to be timing standard; which would be an entirely different thing. >>> But, this is time-nuts, so I should have realized... >>> Anyway, is there a standard, or at least an accepted practice, for how >>> holdover is handled in a time standard? >> >> There are many ways how to do that and which one you choose depends >> on the application and its requirements. You can find everything between >> "jump imediatly" and "just keep the frequency stable and don't care about >> alignment". >> >> Attila Kinali >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com <mailto: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.