Abstract: A demodulator for a digital code differential phase shift modulated signal comprising: an input transducer for launching surface acoustic waves corresponding to a received modulated signal; a plurality of output transducers each of which is arranged to produce an output signal dependent on the relative phases of a number of successive code elements of said surface acoustic waves, each output transducer producing a larger output signal, in a predetermined sense, than any other output transducer when said successive elements have a particular phase relation, different for each output transducer; and means responsive to the relative magnitudes of the outputs of said output transducers.