GPS signal acquisition with USRP 2953R

[JM1800]

Hello all,

How do I set up a USRP 2953R do receive GPS signals? I have a VERT900 antenna connected to the GPS ANT port of the USRP but in the example VI "niUSRP EX Rx with GPS", I can't reference that port in the "Active antenna" field. I can only put things like TX/RX or RX1 etc. What values should I put in the other fields as well? I know the L1 band is 1575.42 MHz.

[ErikL]

Some clarification...

1. the 295x have an integrated GPSDO.  This includes a GPS and an OCXO.  With no antenna the OCXO provides a higher frequency accuracy than the traditional TCXO crystal.  With an antenna (and a strong outdoor lline of sight link to multiple satellites) your OCXO is disciplined off of the GPS satellites making it nealry as good as a Rubidium clock.

http://www.ni.com/tutorial/14705/en/

2. It turns out that a USRP can also be used to recieve and record GPS signals, but this is different.  In that case you would hook the GPS antenna to the front panel connector.  But you wouldnt' see any thing for several reasons.  First you would need to power the antenna.  Next you would need to amplify the signal (GPS is typically -175 dBm).  And the signal is spread spectum and hidden in the noise floor so even after all of that you still won't be able to 'see' it.  Howeve we've successfully used record and playback techniques (and generation techiques with the GPS toolkit) and the USRP works quite well for both.

http://www.ni.com/white-paper/13881/en/

[vvkakade · Accepted solution]

Hi,

The example that you have posted shows you how to acquire a RF signal on the RF ports of the USRP with the internal clock and reference sources set to GPS.

For it to work properly you need to have a GPS antenna connected to the GPS terminal on the device and installed in a place which receives a good level of GPS signal.

The other antenna control in the diagram defines the port on which to receive the RF signal.

If you want to capture and analyze the GPS (RF) signal itself, you can tune the RF front end (carrier frequency) to the right GPS band frequency and connect your GPS antenna to the RF port.

You can use the simple niUSRP EX Rx Continuous Async.vi in that case (but may not work out due to ultra low GPS RF signal power)

[wghwood]

Hi Could you please tell me where to download the example vi for 'niUSRP EX RX with GPS'. I am very interested in it but cannot find it.

Thank you very much!

[vvkakade]

Hi,

Usually the example can be found here for a 32 bit LabVIEW install:

"C:\Program Files (x86)\National Instruments\LabVIEW <put in your version>\examples\instr\niUSRP\niUSRP EX Rx with GPS.vi"