Well bob's comments & caution are accurate, everything drifts. In your case, if the OCXO is rock solid then you would see a 160 PPM change on the EFC line over 7 days which is a 1mV change on your 6 V full scale, which is fairly easy to measure if you have a 6 1/2 digit DMM.
On Sat, Nov 5, 2016 at 10:43 PM, Bob Stewart <[email protected]> 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. 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 <[email protected]> > *To:* Bob Stewart <[email protected]> > *Cc:* Discussion of Precise Time and Frequency Measurement < > [email protected]> > *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 <[email protected]> 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 > <http://groups.yahoo.com/neo/groups/GFS-GPSDOs/info?soc_src=mail&soc_trk=ma> > > > > > ------------------------------ > *From:* Scott Stobbe <[email protected]> > *To:* Bob Stewart <[email protected]>; Discussion of precise time and > frequency measurement <[email protected]> > *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 <[email protected]> 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 > <http://groups.yahoo.com/neo/groups/GFS-GPSDOs/info?soc_src=mail&soc_trk=ma> > > > > > ______________________________ _________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > <https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > > > > > > > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
