How to ensure 2 USRP to have the same internal FPGA configuration when measuring the same signal?

GNU Radio
1

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

2

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.