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A postdetection diversity system using a phase-correction loop modified by the inclusion of a differential demodulator (DD) or a frequency demodulator (FD) is described. Binary and quaternary digital modulation for DPSK and digital FM are considered. An analysis considering additive Gaussian noise shows that, although the diversity combiner proposed is inherently the postdetection type, the well known predetection equal-gain combining (EGC) or maximal-ratio combining (MRC) action can be approximately achieved. A unified analysis of bit error rate (BER) is presented for a Rayleigh fading environment, and fairly simple results are obtained. It is shown that the diversity gain of postdetection EGC is about 0.62 dB inferior to that of postdetection MRC when two-branch diversity is employed.