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An unusual signal with dual properties has been evolved such that the waveform has one of three possible frequencies in each digit time slot as well as four phases at the transition points between the digits. Such characteristics permit the recovery of the original data input either by noncoherent FM or by differentially coherent phase detection, depending upon the characteristics of the transmission medium. At the same time, the signal affords two-to-one bandwidth compression compared to binary systems. Expressions for the constraints imposed on the system and for power spectral distribution are developed. Finally, a simple and straightforward embodiment of the concept as well as certain empirical results are presented in detail.