I am using VSA and matlab to do QPSK and IQ Imbalance things. I opened the measured data (sdf-format) in VSA and resave it as trace and recording in mat-format. Then I loaded those data and ploted them.
However, in trace document the points locate only around the constellation, while in recording document there is a lot of points in the middle. The amplitudes are also different.
In the pic, above is the first 4096 points in the recording, below is the points in trace.
Could anyone help me?