# GPSDO and B2100 **URL:** \ **Category:** GNU Radio\ **Created:** [February 19, 2015, 7:51pm UTC](https://www.ruby-forum.com/t/gpsdo-and-b2100/234268 "2015-02-19T19:51:40Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [February 19, 2015, 7:51pm UTC](https://www.ruby-forum.com/t/gpsdo-and-b2100/234268/1 "2015-02-19T19:51:40Z")
Hello, I recently installed a board mounted GPSDO (TCXO) on my B2100. Specifically I am using this in a USB powered mode and the web-site did say that the TCXO works off the USB power. I am using a passive antenna at the moment. Now most of the time I get warning display “No GPRMC message found”. Only in two cases during the day have I seen the green LED on the GPSDO turn on, in which case the warning message went away, so I know all is well with the board and the mount. Now my questions: (i) Is there a way to force the B2100 to use the internal clock and not wait for the GPS fix for all applications? For example I don’t want to change the uhd\_usrp\_proble executable, but would like the board to use the internal clock and not wait for GPS fix. Is there a way to toggle the mode from automatic to internal clock for all applications via a jumper or other means? I don’t want to recompile other working applications just because I have installed the GPSDO. (ii) Does the active antenna work of USB power? (ii) Once the GPS actually starts working, how can I use gpsd to get the gps data. That is, the web page [USRP Hardware Driver and USRP Manual: Internal GPSDO Application Notes (USRP-B2x0 Models)](http://files.ettus.com/manual/page_gpsdo_b2x0.html) says “Other information can be fetched as well. You can query the lock status with the gps\_locked sensor, as well as obtain raw NMEA sentences using the gps\_gprmc, and gps\_gpgga sensors. Location information can be parsed out of the gps\_gpgga sensor by using gpsd or another NMEA parser.” The last sentence is what I want. I do have gpsd and gpsdx installed on my Mac. However neither can be configured to actually get the data from the GPSDO module. For example the options in the gpsdx does not see an external USB GPS to begin with. Any suggestions are welcome. Thanks, Sharath ---
**Author:** ![Sharath\_A](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/58f4c7/32.png) [@Sharath\_A](https://www.ruby-forum.com/u/Sharath_A)\ **Post date:** [February 20, 2015, 9:35am UTC](https://www.ruby-forum.com/t/gpsdo-and-b2100/234268/2 "2015-02-20T09:35:08Z")
On 02/19/2015 07:47 PM, Sharath A. wrote: > Now my questions: (i) Is there a way to force the B2100 to use the > internal clock and not wait for the GPS fix for all applications? For > example I don’t want to change the uhd\_usrp\_proble executable, but > would like the board to use the internal clock and not wait for GPS > fix. Is there a way to toggle the mode from automatic to internal > clock for all applications via a jumper or other means? I don’t want > to recompile other working applications just because I have installed > the GPSDO. There’s no jumper or hardware way (short of taking out the GPSDO). You can call set\_clock\_source() (see the manual: [USRP Hardware Driver and Device Manual: uhd::usrp::multi\_usrp Class Reference](http://files.ettus.com/manual/classuhd_1_1usrp_1_1multi__usrp.html#a73ed40009d0d3787c183d42423d25026)) If you’re using GNU Radio & Python, that won’t require a recompile (see the GR manual: [GNU Radio Manual and C++ API Reference: gr::uhd::usrp\_sink Class Reference](http://gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__sink.html#aac2a32bcaa207c18a0b8c037760508e6)). > (ii) Does the active antenna work of USB power? You should be good, but in general, GPSDO+2x2 MIMO pushes what bus power can provide and is considered unreliable. > (ii) Once the GPS actually starts working, how can I use gpsd to get > the gps data. That is, the web page > [USRP Hardware Driver and Device Manual: Internal GPSDO Application Notes (USRP-B2x0 Models)](http://files.ettus.com/manual/page_gpsdo_b2x0.html) says “Other > information can be fetched as well. You can query the lock status > with the gps\_locked sensor, as well as obtain raw NMEA sentences > using the gps\_gprmc, and gps\_gpgga sensors. Location information can > be parsed out of the gps\_gpgga sensor by using gpsd or another NMEA > parser.” The last sentence is what I want. I just had a very brief look at the gpsd man page, and it seems it works with devices that are directly connected to the PC – this isn’t how the B2x0 + GPSDO where intended to be used (you won’t find an ‘attached GPS device’ on USB anywhere). If you want to use gpsd, you’ll probably need to ‘fake’ such a device by polling the NMEA strings. Maybe someone out here has done that before? Cheers, M