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Allocation of I- and Q-Signal is faulty

Question asked by Headnut on Jan 13, 2012
Latest reply on Jan 13, 2012 by Headnut

Iam using the N9010A-EXA-Analyzer with the 89600 VSA Software.

When i demodulate a digital modulation for example a QPSK with IQ imbalance (the I-signal has a higher amplitude than the q-signal), the vector diagramm don't shows a constant constellation. The expected "rectangle" is there, but changes its state all the time. Sometimes the I-Signal has the higher amplitude, sometime the Q-signal. So the Software switches the phase of the demodulated signal all the time and the allocation of the I- and Q-Signal is faulty.
This effect i have all the time.

The RF modulated signal is done by the Agilent N9310A RF Signal Generator, which gets an external I/Q-Signal.