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Quadrature modulation dominates all modem communication systems. Gain and phase mismatches or imbalance between the two paths, either in the transmitter or the receiver, degrade the isolation between the supposed orthogonal components. A number of schemes exist to digitally correct the imbalances. Most of these schemes perform the correction in the time domain where the data and degradation effects is directly observed. The FFT in an OFDM receiver offers the opportunity to probe, observe, and correct the imbalance effects in the frequency domain. We present a technique that makes use of the FFT to probe, resolve, and compensate the imbalance contributions of both transmitter and receiver.