Electroabsorption modulators (EAM) have been widely used in externally modulated RF link. In the conventional intensity modulation format, the RF efficiency of such link is critically dependent on the optical saturation of the EAM and the fiber dispersion. In an effort to minimize the dependence on these two factors, we have conducted an experimental study of an optical mixer that employs two heterodyned lasers to generate an optical local oscillator (LO). In contrast to the conventional schemes where both laser beams are launched into the same EAM, the EAM in the present scheme modulates only one of the laser beams. In this way, improvement in RF gain is obtained since it is not limited by the optical saturation of the EAM. The resulting optical spectrum shows that this scheme is equivalent to the optical single side band transmission. For sub-octave bandwidth applications, the dispersion effect in the fiber can be ignored.