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
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