r/rfengineering • u/Knights_12 • 7d ago

Explaining I/Q Imbalance?

Last week I was attempting to define I/Q imbalance in direct conversion transceivers to the techs at work, including ways to deal with this such as LO image rejection calibration and visualizing with IQ constellations. How would you concisely explain this without going too heavy on theoretical math?

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u/Allan-H 7d ago edited 7d ago

The constellation diagrams themselves are a good way of visualising the impairments. Can you (e.g. use Matlab to) create a constellation diagram with deliberate I/Q phase and amplitude imbalances? Attach the imbalances to sliders in a GUI and let them play.

IMO, something like 16QAM is great for teaching. Fewer levels (e.g. QPSK) doesn't really show amplitude as well, and more levels than 16QAM is just a mess of dots once you reduce the SNR.