An apparatus for decoding a data modulated signal includes a signal receiver that receives a data modulated signal that is encoded with phase-shift keying (PSK) and provides an amplified signal corresponding to the data modulated signal, a tunable phase shifter that receives a local reference signal and a selected phase shift, applies the selected phase shift to the local reference signal to produce a phase shifted reference signal, a summing unit that sums the amplified signal and the phase shifted reference signal to produce a summed signal, an amplitude detector that determines an amplitude of the summed signal, and a symbol detector that varies the selected phase shift and determines a current symbol within the data modulated signal based on the amplitude of the summed signal as the selected phase shift is varied. A corresponding method is also disclosed herein.