Hi Bob, Could you expound on "so far below a number of issues"? In any case, your post implies that something else is aging. I'm using an ADR4533A as my voltage reference. That feeds an AD8638 op-amp driving an MMBT2222A pass transistor. That pretty much leaves the divider resistors on an AD8638 in the EFC string. But, aging is aging from my point of view. I guess I could prove that by hooking the EFC to my 3456A and plotting that over a few days.
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> Sent: Saturday, November 5, 2016 8:46 PM Subject: Re: [time-nuts] Thermal impact on OCXO Hi My experience is that the aging on these oscillators is so far below a number of issues that you will not be able to see it in under a year on a > 10 year old unit. Bob > On Nov 5, 2016, at 9:06 PM, Bob Stewart <b...@evoria.net> wrote: > > Hi Bob, > > But will any of the things you mentioned show up as a more or less linear > march downhill at about 1 step per hour over the course of 7 days? In fact, > I think Dan's units show about the same -1 per hour, and he's had them > running continuously for many months. I believe you use these same OCXOs, > Bob. They're Trimble 34310-T units salvaged from China. What's been your > experience with them over the long run as far as aging is concerned? > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > From: Bob Camp <kb...@n1k.org> > To: Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Saturday, November 5, 2016 7:37 PM > Subject: Re: [time-nuts] Thermal impact on OCXO > > Hi > > 2^20 is roughly 1 ppm. It is about 5 uV on a 5V line or 2.5 uV on a 2.5 V EFC > center. > > A DAC that does 100 ppm / C is a pretty typical part. 10 ppm / C is >unusually good > A “good” voltage reference might do 2 ppm / C > A very typical room will swing around +/- 2C without much going on. > Open the door in the room or open a window and 10C is not unusual. > Grabbing a normal banana plug with your fingers will give you > 10 uV, >other thermocouples are running around > A DAC with < 10 uV of noise in the 0.01 to 1 Hz region is unusually good > > That’s just looking at the easy to measure part of the system. A few hundred > uV delta on > the PCB between the OCXO ground pin and “ground” from grabbing the OCXO is > harder > to measure, but also pretty typical. It sums right into the EFC line. > > It’s not a rabbit hole so much as the details of the design at the level you > have chosen > to look at. > > Bob > > > On Nov 5, 2016, at 8:10 PM, Bob Stewart <b...@evoria.net> wrote: > > > > This seems to be turning into a rabbit hole from which there can be no > > possible return. With no evidence, you question my competence and cast > > aspersions on my testing methodology. I give up. > > > > Have a nice day. > > > > Bob ----------------------------------------------------------------- > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > > From: Azelio Boriani <azelio.bori...@gmail.com> > > To: Discussion of precise time and frequency measurement > > <time-nuts@febo.com> > > Sent: Saturday, November 5, 2016 7:02 PM > > Subject: Re: [time-nuts] Thermal impact on OCXO > > > > ...with a 20bit DAC, a suitable voltage reference for that DAC and an > > HP3458... > > > > On Sun, Nov 6, 2016 at 12:39 AM, Bob Stewart <b...@evoria.net> wrote: > >> Hi Hal, > >> > >> With a 20 bit DAC, even a small aging rate is going to show up. I'll let > >> the one GPSDO cook for a month or so and see what it shows then. I'll > >> also pull the data from the log file and see if I can see any correlation > >> between the temperature and the EFC over time. IOW, for data points > >> separated by 3.5 days, does the temperature difference between the two > >> point seem to play a large part of the change in the recorded DAC value. > >> > >> The graph was made from the logging data sent to the PC. But, the > >> firmware doesn't have access to historical data on the PC, so something is > >> needed for aging calculations. Tom mentioned here recently about the > >> 58503A GPSDO saving 64 hours of data for it's aging calculations. So, I > >> just added a few hours to that to get to 3.5 days of history in the GPSDO. > >> Bob ----------------------------------------------------------------- > >> AE6RV.com > >> > >> GFS GPSDO list: > >> groups.yahoo.com/neo/groups/GFS-GPSDOs/info > >> > >> From: Hal Murray <hmur...@megapathdsl.net> > >> To: Bob Stewart <b...@evoria.net> > >> Cc: Hal Murray <hmur...@megapathdsl.net> > >> Sent: Saturday, November 5, 2016 6:23 PM > >> Subject: Re: [time-nuts] Thermal impact on OCXO > >> > >>> The OCXO has been hot for a number of months. > >> > >> Then I don't understand why it is still aging that much. > >> > >> > >>> I changed the firmware to save the DAC voltage every 30 minutes for 3.5 > >>> day > >> > >> That's not very long. > >> > >> How did you make the graph? You had to get the data out to a place where > >> you > >> can plot it somehow. If you can do that, why are you "saving" the data? I > >> assume you have a serial port to a PC or something like that. > >> > >> > >>> The fuzz in the temperature line is, indeed, the HVAC cycling > >> > >> You could try putting a box over the unit to see if that slows down the > >> temperature changes. > >> > >> Mostly, you are trying to block air flow. > >> > >> > >> > >> -- > >> These are my opinions. I hate spam. > >> > >> > >> > >> > >> > >> > >> _______________________________________________ > >> 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. > > _______________________________________________ > 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.