Forum: GNU Radio How to ensure 2 USRP to have the same internal FPGA configuration when measuring the same signal?

Hi Folks,



I have managed to use 2 different USRP N210's to measure the same signal
with the same sampling rate (both center at 0 Hz DC) at approximately 
the
same time (timing is an issue but irrelevant for this discussion).
Examination of signal intensity does confirm the above to be true. 
However,
when I compare individual tones between the 2 units, I see the phase
differences between the tones jump around a lot. And they seem to 
cluster at
+90/-90 locations.



This is very puzzling and troublesome. I guess internally the USRP
configures the FPGA in a way that is not visible. Is there a way that I 
con
force the 2 USRP to configure the FPGA in the same identical 
configuration
when taking data?



Thanks for your inputs and help.



LD

On 01/23/2013 03:16 AM, LD Zhang wrote:
>
> This is very puzzling and troublesome. I guess internally the USRP
> configures the FPGA in a way that is not visible. Is there a way that
> I con force the 2 USRP to configure the FPGA in the same identical
> configuration when taking data?
>
> Thanks for your inputs and help.
>
> LD
>
>
You aren't synchronizing the two N210s with an external clock reference,
so there's no way there'll be phase coherence between the two devices.