Why N210 generates X shape IQ constellation?

[Amir2]

Hi all,

As a transmitter, N210 transmittes QPSK IQ data samples. But when I monitor it (with another USRP), I see that the QPSK IQ constellation looks like X (shown in photo below) instead of standard IQ constellation. Does anybody know why is that? Any experiences? Do I need to do any software updates for the N210? 

PS: There is no issue in the monitoring part and it works perfect. The issue is caused from the transmitter part (USRP N210).

Thank you.

[WillyWad]

Hey Amir,

Can you describe what you're transmitting and how? As you said, the constellation does not look anything like QPSK. The fact that the constellation isn't just random points makes it look like you are receiving and demodulating correctly, like you said, so we are not transmitting correctly. I would suggest running an example that generates QPSK and comparing those results. I expect the example would give us something like the standard constellation below. If it does not, we have other problems. 

-Will