A highly efficient subcarrier modulation technique, suppressed clock pulse duration modulation (SCPDM) has been developed that outperforms narrow-band frequency modulation in very noisy channels. Developed primarily for hard limiting satellite repeaters, the technique utilizes a phase-shift key (PSK) carrier and phase-lock demodulators. The SCPDM technique is shown to be extremely useful and cost effective where the overall objective is to obtain maximum traffic rather than toll quality voice communication. Design considerations are discussed and test data from a typical hardware implementation are presented.