Hi I would suggest you read the papers on the subject. They are out there. Even over a few days OCXO aging is likely to be non-linear ( => curved, not straight line). On an OCXO that is warming up, your are dealing with retrace rather than aging. This can have an impact for a few months after turn on. I have one unit in the basement that took 9 months to come out of retrace after being in storage for “a while”. It was an eBay item so no idea just how long the power off time was.
Bob > On Nov 7, 2016, at 12:47 PM, Bob Stewart <b...@evoria.net> wrote: > > Hi Bob, > > When you say that OCXOs don't age in a linear fashion, what does that mean? > IOW, is this a case where it's almost linear over a week, and the > non-linearity is only detectable when you consider the longer term? If > that's the case, then it seems reasonable to use the past 3 or so days of > data collection to project the near-term behavior; where near-term is less > than 3 days into the future. > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > From: Bob Camp <kb...@n1k.org> > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency > measurement <time-nuts@febo.com> > Cc: Scott Stobbe <scott.j.sto...@gmail.com> > Sent: Monday, November 7, 2016 6:08 AM > Subject: Re: [time-nuts] Thermal impact on OCXO > > Hi > > > > On Nov 5, 2016, at 10:43 PM, Bob Stewart <b...@evoria.net> wrote: > > > > Hi Scott, > > D'oh. Thanks for the correction! Like I said, I don't do these > > calculations often. > > > > If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit > > stumped. I do have an op-amp in the EFC string with a voltage divider for > > gain. The resistors are Panasonic ERA-6AEDxxxV resistors. Mouser says > > they're temperature stable to 25PPM/C, but of course they don't mention an > > aging rate. I don't really see anything else, other than the OCXO, that is > > likely to be prone to a linear type of aging. > > OCXO’s don’t age in a linear fashion. At least 90% of them don’t. If you dig > into the FCS papers there are various > curves proposed as models. Mil-O-55310 has one of them as the “official” > approach. All of them have the basic > issue of mistakenly fitting to to short a time constraint. > > Bob > > > The aging rate appears to be stable from unit to unit, so naturally I > > considered the OCXO first. > > > > There is one other bit in the EFC string that might be controversial, but I > > don't see that it would be a candidate for the symptoms of aging. > > > > Bob > > ----------------------------------------------------------------- > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > > From: Scott Stobbe <scott.j.sto...@gmail.com> > > To: Bob Stewart <b...@evoria.net> > > Cc: Discussion of Precise Time and Frequency Measurement > > <time-nuts@febo.com> > > Sent: Saturday, November 5, 2016 9:19 PM > > Subject: Re: [time-nuts] Thermal impact on OCXO > > > > If your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the EFC > > range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1 LSB is > > ~1PPT. So, if everything else is stable the DAC code reflects changes > > solely due to the OCXO, which would be an aging of 24 PPT/day. > > On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <b...@evoria.net> wrote: > > > > Hi Scott, > > The 20 bits span about 6 volts. The EFC range spans about 8Hz (+/-4Hz). I > > don't do these calculations every day, but that's about 4.5PPT? > > Bob ------------------------------ ------------------------------ ----- > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > > > > > > > > From: Scott Stobbe <scott.j.sto...@gmail.com> > > To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency > > measurement <time-nuts@febo.com> > > Sent: Saturday, November 5, 2016 8:38 PM > > Subject: Re: [time-nuts] Thermal impact on OCXO > > > > I think that's a nice plot, it looks like you have stepped 160 LSB over 7 > > days or roughly 1 LSB per hour. With a 20bit dac you are trimming maybe 1 > > ppt/LSB to 4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB, solely > > due to drift, you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the case of > > 4ppt/hour your at 1E-12 at 1280 s. Seems reasonable. > > On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <b...@evoria.net> wrote: > > > > Oh dear. I attached the wrong file. Here's the correct one. > > ----------------------------- ------------------------------ ------ > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > > > > > > > > ______________________________ _________________ > > 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.
