Typo, "Aging [PPM]" should read "Aging [PPB]". On Mon, Nov 7, 2016 at 10:34 AM, Scott Stobbe <scott.j.sto...@gmail.com> wrote:
> Here is a sample data point taken from http://tycho.usno.navy.mil/ > ptti/1987papers/Vol%2019_16.pdf; the first that showed up on a google > search. > > Year Aging [PPM] dF/dt [PPT/Day] > 1 180.51 63.884 > 2 196.65 31.93 > 5 218 12.769 > 9 231.69 7.0934 > 10 234.15 6.384 > 25 255.5 2.5535 > > If you have a set of coefficients you believe to be representative of your > OCXO, we can give those a go. > > On Mon, Nov 7, 2016 at 7:08 AM, Bob Camp <kb...@n1k.org> wrote: > >> 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/m >> ailman/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.