Modulation and demodulation in the minimum (frequency)-shift keying (MSK) format are reduced to the form of coherent biphase keying. Considerable simplification of circuitry is thus effected without sacrifice of performance. When the ratio of the carrier frequency to the bit rate is high, then the technique described here does not require the precise relative phasing of any pair of oscillators in the transmitter. Experimental results demonstrate the feasibility of synthesizing the one filter that is unique to this signaling scheme. In the present instance, the filter is realized as a surface acoustic wave device.