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In this paper, joint iterative demodulation and decoding of differential frequency hopping (DFH) signals based on the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm is considered. The DFH is a nonlinear modulation with memory in the frequency sequence of the successive transmitted symbols, which can be represented by a trellis diagram. The proposed receiving scheme is primarily composed of an a posteriori probability (APP) decoder/filter and an APP demodulator, by which the extrinsic information on the coded bits extracted from the output of the APP filter can be utilized again by the demodulator as updated a priori information. Performance over AWGN and time-varying Rayleigh flat fading channels is investigated by Monte Carlo simulation. By comparison between the symbol-by-symbol maximum a posteriori probability (SBS-MAP) detection with soft decision Viterbi decoding and the proposed method, it can be shown that considerable improvement can be achieved for both static and time-varying fading channels.