In modern wireless communication devices cost- and areaeffective signal processing architectures are essential. Flexible and reconfigurable front-end solutions are necessary to achieve high spectral efficiency. Direct conversion transceivers are suitable but have to deal with I/Q mismatch, which, for large bandwidths become frequency selective. In order to keep costs low the specifications for the analog components can be reduced, if the compensation of the resulting impairments is done by digital signal processing. Without the knowledge of any transmit data, blind I/Q mismatch compensation can be based on a second-order statistical property called properness, which is valid for a large class of digitally modulated communication signals and which is destroyed by I/Q mismatch. A novel DSP-algorithm for blind adaptive I/Q mismatch compensators using only real-valued filters is proposed. The impact of other RF-impairments, like nonlinear even-order distortions resulting from finite mixer isolation, on the properness measure is investigated.