We present an original electro-optical microwave mixer based on a SOA directly modulated by a local oscillator (LO) in presence of a RF signal. We obtain a good conversion gain of about 5.7 dB and a low Error Vector Magnitude (EVM) below 3.8 % proving the ability of the mixer to achieve a frequency down-conversion from 2.4 GHz to 100 MHz of an optical complex-modulated RF signal: QPSK, 16QAM and 64QAM.