GPS Receiver for USRP2

GNU Radio
1

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

2

Quoting M. [email protected]:

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

3

On 03/10/2010 01:11 AM, Per Z. wrote:

code (which uses the VRT branch). The next step for me is to use a real
GPS but other duties has taken over…

This is correct, you do not need to use a GPSDO, you can lock to any 10
MHz reference. And any digital signal source will suffice, it does not
need to be a pulse per second source.

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

At power up the clock generator is not attempting to lock to the
reference. It does not attempt that until the processor tells it to do
so, which only happens after the processor is running, roughly 3 seconds
after powerup. If you connect the reference to the USRP2 after it is
powered up, it should lock in less than a second.

Matt