We are using a ZC706 board with FMCOMMS-3 and transmitting and and receiving on the same board. Using a digital BIST loopback, the constellation is fine but using the antennas provides the attached constellation. It seems like the constellation points are dispersed. My question is: visually looking at the constellation diagram attached, is it affected by frequency offset ? If not, can you tell what's causing the dispersion and rotation of points?
Also, the second picture I attached has the output of my signal that I expect to have a flat amplitude but seems to be modulated with a low frequency sinusoidal. How can I fix that?