Hi The OCXO “as shipped” on units after about 2021 or 2022 is in the low parts in 10^-9 over -20 to +70. Is yours 1 x 10^-9 or 2 x 10^-9? there’s no easy way to tell.
If you assume the TC is linear ( it may not be …) that gets you into the 10 to 20 ppt / C range. With a room that swings a couple of degrees, that’s going to be tough to measure ….. Even if the TC is a bit non-linear, it’s unlikely you are over 40 ppt / C. Bob > On Jul 24, 2021, at 2:30 PM, Stewart Cobb <[email protected]> wrote: > > A few days ago, Charles Steinmetz mentioned that even the "good" > Thunderbolts with the 37265 OCXOs fall into two groups, one 100x worse than > the other. Perhaps that difference is not due to the OCXOs themselves but > to other parts on the board. > > We know that, during the production run, the high-resolution board > temperature sensor was replaced by a software incompatible chip which > resulted in much coarser temperature resolution. We don't know how that > measurement was used in the control loop. > > I gave a writeup of the OCXO control DAC here: > > <https://www.febo.com/pipermail/time-nuts/2013-November/081058.html> > > I forgot to mention in that writeup that the 74AC174 flip flop that > implements the PWM output gets its power from a precision voltage reference > chip. This stabilizes the DAC voltage over temperature. That reference, or > the precision opamp that serves as a level shifter for the DAC, might have > been substituted for parts with worse tempco at some point in the > production run. Either of those could cause an apparent increase in > observed tempco for the system as a whole. > > It's even possible that the "good" units had offsetting temperature > coefficients between the OCXO and the DAC, and that insignificant parts > changes destroyed that favorable offset, even though all the parts remained > within spec. > > The only good way to find out would be to examine all the date codes and > part numbers on the relevant parts, and to compare a group of "good" units > with a group of "bad" units and look for correlations. > > Still if someone wants a project ... > > Cheers! > --Stu > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
