We've been using the 89601b custom OFDM demodulation software for many years now and at some point along the way we have found cases where we are not getting accurate or meaningful I/Q imbalance measurements. IQQuadErr and IQGainImb seem to be reporting at near-zero values when the EVM is degraded as one would expect (connecting a signal generator directly to an MXA/PXA). The constellations we see and the EVM we see reported make sense.
It is possible that there is just a scale factor error (such as reporting 0.08 degrees when the source has 8 degrees dialed in), but I am not quite sure it is that simple.
Some older versions kicking around (14.23 /15.0) seem to provide meaningful results, but I have specifically tested some versions between 17.x and 20.2 and the results are just plain incorrect.
The waveform is relatively simple and repetitive. Has anyone else seen this problem?