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Re: [Discuss-gnuradio] GPS Receiver for USRP2

From: Per Zetterberg
Subject: Re: [Discuss-gnuradio] GPS Receiver for USRP2
Date: Wed, 10 Mar 2010 10:11:09 +0100
User-agent: Internet Messaging Program (IMP) H3 (4.0.5)

Quoting Madan <address@hidden>:


 I am choosing the GPS receiver to make the timing synchronization between
the two USRP2's. I have already placed an order, and it would take few days
to reach here.
Mean while , i wanted to learn about how to synchronize the USRP2's using
GPS reciever,  Can anyone guide me  , how to ?

and from where i can get some useful material or information to setup and
synchronize USRP2's using GPS receiver...!

By searching the google , i had found some information regarding the USRP2

relating to calling the function
config_mimo(MC_WE_LOCK_TO_SMA) and sync_to_pps( )

for locking to USRP2 to external clock 10MHz and 1PPS,

My question is Can anyone give me a clear picture, how to configure these
programs and to synchronize two USRP2's.
I am not going to use MIMO(using to MIMO cable given) configuration right
now, currently i am only focusing on SISO config.

If synchronising USRP2's in MIMO case is different from SISO, can you please

Thanks in advance

I can just tell you about my experience (for what is worth :-). I synchronized the TX and RX using a 10MHz reference from a signal generator. I filtered the 10MHz using a band-pass filter from mini-circuits and then splitted with a mini-circuits splitter. Then I connected a step function to the pps inputs which I manually triggered. I modified the apps for transmitting and receiving samples which are somewhere under usrp2/apps or something like that. I had a ten second sleep in the program to be able to start both USRP2s and manually trigger the step function. It seemed to work great with very repeatable results (basic db-boards cable between TX and RX). I can send my ugly code (which uses the VRT branch). The next step for me is to use a real GPS but other duties has taken over...

One thing more.
When I cold start the USRP2s it seems to take some seconds before they are firmly locked to the 10MHz reference.

This shows that a GPS is not strictly needed.


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