Re: [Discuss-gnuradio] GPSDO and B2100

[Martin Braun]

On 02/19/2015 07:47 PM, Sharath Ananth wrote:
> 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.

There's no jumper or hardware way (short of taking out the GPSDO). You
can call set_clock_source() (see the manual:
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:
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
> 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

> 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
> 
> 
> 
> 
> 
> 
> 
> 
> _______________________________________________ Discuss-gnuradio
> mailing list address@hidden 
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>