The preambles of narrow band signals and DSSS signals are prepared for compatible detection. The preamble is encoded by encoding a sequence of identical preamble blocks with sequentially corresponding code elements of a preamble encoding sequence. Each of the identical preamble blocks has the same predetermined pattern of code elements. When the signal is a DSSS signal, the preamble is a spread preamble in which each of the blocks has a number of code elements corresponding to a spread-factor multiple of the number of code elements in a block of an unspread preamble for a narrow band signal. The preambles of both types of received signals are detected by processing a metric representing detected coherent energy with a metric representing detected noncoherent energy, after first determining that the detected noncoherent energy is greater than the average energy of the received signal.