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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