CHIRP modem is introduced first.Then the algorithm of soft decision decoding of Golay (24
12) used in this modem is discussed.We synthesized some techniques to design a fast and flexible scheme of soft decision decoding.The decoding time and coding gain of this scheme are tested under on HF channel simulator
and the result of test is satisactory.We also raised a new scheme to evaluate PBER
one of the most important we analyzed the characteristic of PBER evaluation according to the simulation results and discussed some schemes to improve the performance of PBER evaluation.