Re: [Discuss-gnuradio] GPS Receiver for USRP2

[Per Zetterberg]

Quoting Madan <address@hidden>:

> Hi
>
>  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
> sychroniztion.
>
> 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
> differentiate.
>
>
> Thanks in advance
> MADAN

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.


BR/
Per