Re: [Discuss-gnuradio] Synchronization issue with multiple USRPs

[Josh Blum]

On 04/26/2011 11:22 AM, Khalid Jamil wrote:
> Please correct me if I am wrong. I think that this random channel-channel
> phase offset at each acquisition depends on when each usrp 100MHz LO locks
> to 10MHz external frequency reference by PLL. How PPS will help in that
> case? Unless PPS is locked somehow to 10MHz clock?
> 

Yes, but I strongly recommend that you get time-aligned samples working
before trying to calibrate for the LO phase offsets.

In your GRC flowgraph, each USRP source block will provide samples that
start at a different random time that could be offset by many
milliseconds. I don't think you want that?

In order to get time-aligned samples from N devices, you must

1) synchronize the the time registers (seconds/ticks) across all USRP
devices. You should use the PPS to do this

2) tell the devices to stream at the same time.

> Is there a good example to follow, may to start with 2 or 4 channels?
> 

There is an example that comes w/ uhd called rx_multi_samples. if you
want to do this in GRC, follow the instructions in the previous email.

-Josh