Amplitude and relative phase measurement of noisy CW signals require appropriate techniques, such as coherent detection, for maximum dynamic range and accuracy. We hereby describe a two channel system, developed for satellite microwave propagation beacon experiments, that comprises a user developed card, a DSP kit and dedicated software. The solution, that uses digital signal processing programmable chips and a DSP software managed PLL offers considerable advantages over a classical analogue system. Several prototype experimental results, tested with realistic signals, are presented and discussed.