Hi Stephan, I'm not sure if moving the power resolved your issue, but I wanted to follow up now that we have completed our root cause analysis. The GPSDO requires a minimum of 5.7V to retain accuracy and the voltage on J509 is dropping below that during TX and/or RX. The resolution is to first move the GPSDO power from J509 to J102 on the motherboard. If that does not resolve the issue, add solder to between the center pin and back plate of the front panel power connector (J101).
We are putting in place RMA rework instructions, so you may contact supp...@ettus.com to arrange for an RMA to have the rework done if you are not comfortable or capable of doing it yourself. Best regards, Michael On Fri, Nov 16, 2018 at 5:47 AM Stephan Esterhuizen < stephan.esterhui...@spire.com> wrote: > Thanks for the tip Michael. I'm on travel at the moment, and will try this > next week when I get back to the lab. I'll report my findings to mailing > list. > > Cheers > > Stephan > > On Wed, Nov 14, 2018 at 1:09 AM Michael West <michael.w...@ettus.com> > wrote: > >> Hi Stephan, >> >> Try moving the GPSDO power from the J509 connector to the J102 connector >> on the N200 motherboard. J102 is 6V AUX power and does not sag when >> running. The provided cable is a little short, so you will have to get >> creative. Give that a try and let us know if it solves the problem. >> >> Regards, >> Michael >> >> On Sat, Nov 10, 2018 at 9:33 AM Stephan Esterhuizen via USRP-users < >> usrp-users@lists.ettus.com> wrote: >> >>> Hi Robin, >>> >>> Thank you for the reply. I have debugged the problem more and realized >>> two issues. >>> >>> 1) The massive drift of 14 microseconds/second was due me using a 6V, 2A >>> brick supply. This is my fault! After switching it out for a 3A supply, I'm >>> able to get the GPSDO to lock (GPS_SERVO message returns 6 for lock status >>> field) >>> 2) Once you start collecting data, GPSDO PPS & 10 MHz start drifting >>> from UTC. As mentioned, this is probably due to a voltage sag on the 6V >>> supply for the Firefly GPSDO. >>> >>> For issue 2, I measured the nominal voltage to GPSDO (USRP N200 J509) to >>> be 5.678V (+-2mV), then once I start a data collection, the minimum voltage >>> I see is 5.532V, then after a few seconds of data collection it reaches a >>> "steady state" of 5.545 V. This small change of (5.678-5.545 V) 133 mV is >>> enough to give the PPS a drift of about 5-8 nsec/second. Eventually the >>> GPSDO feedback loop catches this and steers it back to something more >>> acceptable. For reference, the voltage at the input to N200 (J101) is >>> 5.901V+-5mV when idle and collecting samples. >>> >>> This slight deviation of < 100 nanoseconds due to voltage change is >>> fine for my application, I realized I can just read back the GPS_SERVO >>> sensor and get the actual offset from UTC to correct any timestamps. >>> >>> Regards >>> >>> Stephan >>> >>> >>> On Fri, Nov 9, 2018 at 5:09 PM Robin Coxe <robin.c...@ettus.com> wrote: >>> >>>> Hi Stephan. Your issue looks similar to one that has been previously >>>> reported. The Hardware Sustaining Engineering team is currently >>>> investigating. >>>> >>>> Would it be possible for you to try powering the GPSDO module from a >>>> lab supply instead of plugging it in to the N210 motherboard and checking >>>> if your issue still persists? >>>> That would help us determine if you are experiencing the same problem. >>>> Another helpful measurement would be to measure the voltage drop of the 6V >>>> wall wart when the GPSDO IS powered by the N210 motherboard. >>>> >>>> We will keep you and list updated on the progress of the investigation. >>>> >>>> -Robin >>>> >>>> >>>> On Fri, Nov 9, 2018 at 3:06 AM Stephan Esterhuizen via USRP-users < >>>> usrp-users@lists.ettus.com> wrote: >>>> >>>>> Hi All, >>>>> >>>>> I have two N200 USRPs with Jackson-Labs Firefly 1A GPSDO. I'm doing a >>>>> very basic test, where I have a common active GPS antenna split 2 ways >>>>> (with DC block on one N200 GPS antenna port). I then watch the 1PPS from >>>>> each GPSDO on a scope, and unfortunately see the PPS drift by as much as >>>>> 14 >>>>> microseconds per second relative to each other. When this offset reaches >>>>> about 1.5-2.0 milliseconds, I see the PPS relative offset "snap" down to a >>>>> few micro seconds error, but then they immediately start drifting apart >>>>> again. >>>>> >>>>> The N200 GPSDO reports they're locked. I wrote some quick python code >>>>> to query sensors: >>>>> >>>>> ---------------------- >>>>> FIRST N200: >>>>> ---------------------- >>>>> [INFO] [GPS] Found an internal GPSDO: Jackson-Labs, FireFly , Firmware >>>>> Rev 0.929 >>>>> [INFO] [USRP2] Setting references to the internal GPSDO >>>>> GPS lock status: locked >>>>> GPS_GPGGA: >>>>> $GPGGA,095011.00,xxxx.xxxxx,N,xxxx.xxxxx,E,1,10,0.9,320.7,M,46.9,M,,*6C >>>>> GPS_SERVO: 18-11-09 3888 94089 21.81 2.08E-11 13 10 6 0x0 >>>>> GPS epoch time: 1541757012 seconds >>>>> Ref: locked >>>>> >>>>> >>>>> ---------------------- >>>>> SECOND N200 >>>>> ---------------------- >>>>> >>>>> [INFO] [GPS] Found an internal GPSDO: Jackson-Labs, FireFly , Firmware >>>>> Rev 0.929 >>>>> [INFO] [USRP2] Setting references to the internal GPSDO >>>>> GPS lock status: locked >>>>> GPS_GPGGA: >>>>> $GPGGA,095027.00,xxxx.xxxxx,N,xxxx.xxxx,E,1,08,1.1,317.9,M,46.9,M,,*63 >>>>> GPS_SERVO: 18-11-09 2948 120000 796.02 9.59E-09 13 8 2 0x326 >>>>> GPS epoch time: 1541757029 seconds >>>>> Ref: locked >>>>> >>>>> ============ >>>>> >>>>> At this point, it might be a question for Jacksonlabs, since I'm not >>>>> really using any N200 functions except for reading back the Ublox GPS NMEA >>>>> strings. >>>>> >>>>> Has anyone seen this kind of behavior before? >>>>> >>>>> I'm suspecting the GPS_SERVO field might shed some light, but don't >>>>> quite know how to read it. >>>>> >>>>> Thanks for any pointers >>>>> >>>>> Stephan >>>>> _______________________________________________ >>>>> USRP-users mailing list >>>>> USRP-users@lists.ettus.com >>>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>>>> >>>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> USRP-users@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >> >
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