Abstract: RS concatenated with differential frequency hopping G function encoder is proposed for HF differential frequency hopping system. In order to improve the error code rate performance, modified MAP algorithm is applied to the inner decoder of differential frequency hopping G function. (40×40) block weave encoder is used and the outer code is decoded by the Berlekamp Massey algorithm. Simulation results show that the new algorithm overcomes the shortcomings of conventional systems, and that the performance of this differential frequency hopping system is greatly improved.