Hi Even back when they were new, most of these devices got swapped out rather than repaired. The cost to the manufacturer to do a repair that finds everything was simply to high.
Bob > On Jun 17, 2021, at 11:32 AM, Jeremy Elson <[email protected]> wrote: > > After taking the cover off the bad LPRO I finally found the calibration pot > and realized why I hadn't seen it before: the hole in the case that allows > access to the pot was covered by a calibration sticker. > > However, turning it seemed to have no effect at all on the frequency. I > wonder if the unit is just broken. > > Is there anywhere I can send the thing for repair? > > > On Thu, Jun 17, 2021 at 4:20 AM Pluess, Tobias <[email protected]> wrote: > >> Hi Jeremy >> >> when buying LPROs from eBay, be careful! I did this twice and I bought it >> from the same seller. However, one of the "LPROs" I got is actually not an >> LPRO but an SLCR-101. I have not found much information about this, but it >> appears to be a cheaper version of the LPRO. >> >> As far as I know, some of the LPROs have a small hole in the case where you >> can insert a really small screwdriver and adjust some internal >> potentiometers, but not all LPROs have this. Mine has this little hole. >> The SLCR does not have an adjustment hole. You have to open the case to >> adjust things. >> >> Best >> Tobias >> HB9FSX >> >> On Thu, Jun 17, 2021 at 1:11 AM Jeremy Elson <[email protected]> wrote: >> >>> Fellow nuts, >>> >>> This week, I've been working more on my "$5 timestamper" based on the >>> STM32G4 chip. I've finally been able to use it to get some nice results >>> comparing the frequency of a couple of LPRO-101 rubidium frequency >>> standards I have to SI seconds via a GPS receiver. >>> >>> My original email to this list on my new timestamper, in February, had a >>> version of this experiment. Unfortunately it was flawed because there >> were >>> still some bugs in the analog front-end of my timestamper that I had not >>> yet discovered. As a result, there were discontinuities in the timestamps >>> when the clock line going into the timestamping chip had noise >> (generating >>> extra pulses) or wouldn't quite be high enough voltage to go over the >>> chip's threshold (causing missed pulses). These have been fixed, as I >>> reported in my second email on the timestamper (in April). >>> >>> I moved recently, and now that I have GPS set up in my new lab I was >>> finally able to redo my February experiment to measure the frequency of >> two >>> LPRO-101 rubidium standards I bought on eBay for about $200 each. The >>> seller ("test_tool") claimed to have calibrated both before sale. >> However, >>> I discovered the performance of one of them was almost two orders of >>> magnitude better than the other. The test setup was: >>> >>> 1) The device-under-test (LPRO-101) was used as the 10mhz reference clock >>> for my timestamping board. >>> >>> 2) An early eval board of a ublox M10 GNSS (EVK-M101) with a decent sky >>> view, was configured to listen to 3 constellations (GPS, Galileo, >> GLONASS). >>> I did not use location surveying so the accuracy is probably less than it >>> could have been but the reported 3D position was quite stable. >>> >>> 3) The PPS output of the uBlox M10 was attached to one of the >> timestamper's >>> input channels. >>> >>> I did this with two LPRO-101 units. The resolution of the timestamper is >>> currently ~6ns, i.e. the inverse of the 170mhz clock speed of the chip. >> (On >>> my todo list is to create another revision of my board with the >> higher-end >>> STM32G4 chip that will get the timestamper resolution down to 184ps.) I >>> plotted the error in the timestamps of the PPS signal with time, i.e. the >>> x-axis is the time the experiment has been running in seconds; the y-axis >>> is the difference between the actual timestamp and what the timestamp >>> "should have been" if the timestamps were actually received exactly 1 >>> second apart. Ideally it would be a flat line indicating no frequency >>> difference. >>> >>> The better of the two units showed a frequency error (t=10000s) of about >>> 4e-11, which (as I understand it) is typical performance for an RbXO: >>> >>> >>> >> https://www.circlemud.org/jelson/time-graphs/2021-06-16-gpspps-rubidium-unit2-test2-after-warmup.txt.time.plot.png >>> >>> The other unit was about 20x worse, about 1e-9: >>> >>> >>> >> https://www.circlemud.org/jelson/time-graphs/2021-06-16-gpspps-rubidium-unit1-test2.txt.time.plot.png >>> >>> I'm very pleased with the performance of my timestamper, which seems to >> be >>> working perfectly, and I look forward to getting it "cooked" enough to be >>> able to share with all of you. >>> >>> I'm less pleased with the performance of one of the frequency standards, >>> which leads me to my question: has anyone calibrated one of these things >>> before? The manual I found online says I should be able to turn a >>> calibration screw on the cover, but the units I have don't seem to have >> any >>> exposed screws! >>> >>> Regards, >>> -Jeremy >>> >>> PS: If needed, the raw data behind the two graphs below is here: >>> >>> >>> >> https://www.circlemud.org/jelson/time-graphs/2021-06-16-gpspps-rubidium-unit1-test2.txt >>> >>> >>> >> https://www.circlemud.org/jelson/time-graphs/2021-06-16-gpspps-rubidium-unit2-test2-after-warmup.txt >>> _______________________________________________ >>> 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. >> > _______________________________________________ > 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.
