In broadband microwave reflectometry coherent detection is widely used to obtain the phase information and to improve the systems sensitivity, both in diagnostics measuring the electronic density profile and plasma fluctuations. Coherent detection uses a translated version of the probing signal to guarantee a stable Intermediate Frequency (IF). A novel technique to generate the frequency translation by double frequency conversion is here presented and its advantages over the commonly used single frequency conversion techniques employing image rejection mixers are discussed. The results obtained with the new frequency translator modules developed for three JET FM CW reflectometers, operating successfully at JET since mid 2009, are presented.