GPSDO and B2100

GNU Radio
1

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) 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

2

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 USRP Manual: uhd::usrp::multi_usrp Class Reference)

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).

(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 USRP Manual: Internal GPSDO Application Notes (USRP-B2x0 Models) 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