This paper presents an analytical method for evaluation of the error performance ofM-ary differentially coherent phase-shift keyed signals (DCPSK) transmitted through a finite chain of bandpass hard-limiting (BPHL) repeaters. Each link between repeaters is additively corrupted by Gaussian noise and cochannel interference (having the same form as the signal). The system passband is sufficiently wide so that the signal and each interference pass without distortion. The analysis is based on the newly derived phase probability density function of the sum of the signal, noise, and interference. In addition, the performance of the BPHL system is compared with the corresponding performance of a linear system. Also, the interference immunity of CPSK and DCPSK signals is examined. The general observations are similar to those previously discussed for CPSK (referring to the BPHL multilink system) and for DCPSK in the linear channel.