Some digital partical response continuous phase modulation signals such as 3RC, 3SRC, 4SRC, and TFM have cconstant envelope characteristics and compact power spectra. However, their bit error rates in fast fading environments are too high when a simple frequency detection is used. This is due to high inter symbol interference resulting from adjacent bits. The improvement of BER performance by using DFE(Decision Feedback Equalization) to cancel the ISI of one adjacent bit is theoretically investigated in this paper. Numerical resuls are presentes to compare the BER performance of frequency detection with and without decision feedback equalization.