The BER performance of a land mobile radio communication system with GMSK modulation is analyzed using one-bit differential detection. In particular, the effect of the IF filter bandwidth on the BFR is analyzed. The optimum bandwidth for the IF filter is found to be a function of signal-to-noise power ratio, signal-to-co-channel-signal power ratio, and signal-to-delayed-signal power ratio. Several graphs are presented to illustrate the effect of the IF bandwidth in the presence of Doppler spread and frequency-selective fading. >