I used two AD9371（USRP N310）, one as tx and one as rx.
tx sends QPSK data, rx receives data and calculates EVM.
The calculation results show that the EVM of different sub-carriers differ greatly. What may be the cause of this phenomenon？
One reason could be difference in reference clocks. Are you providing same external reference clock to both the evaluation boards ?
If you test the boards separately , Tx monitor is spectrum analyzer and…
Can you share the constellation plot?
The RF frequency used in the test is 3.5GHz.
I will use a lower frequency for testing.