This is the gpsdo compatible module for usrp. it can work with b210 and b200.

Actually it is not gpsdo. it is a gpsdo like module it use individual ocxo plus ublox gps module, where ocxo provide 0.01ppm 10mhz clock and gps module provide pps and gps message.

Because it use individual ocxo so it do not need gps signal to provide high accuracy 10mhz clock. it will always provide high accuracy 10mhz clock. however if you want to use pps or gps message you still need gps signal, so you need to connect proper gps antenna to the "gps ant" port of b210 and put the gps antenna outdoor.

If you want to use gps message you need to modify uhd source code because there is a bug in uhd that can not recognize ublox gps message. the link below show how to fix this bug

http://zhixun-wireless.top/fix-ublox-gps-module-message-bug-in-uhd