Methods and systems are disclosed herein for discriminating phase-shift-key (PSK) modulated signals from frequency-shift-key (FSK) modulated signals in received signal streams. First, a bit frequency analysis is applied to a digital signal stream representing the received signal stream. The bit frequency analysis computes bit frequencies for bit segments within the digital signal stream. These bit frequencies are then summed in an array to form a bit frequency histogram. Second, a bit phase analysis is applied to the digital signal stream. The bit phase analysis computes bit phases for bit segments within the digital signal stream. These bit phases are then summed in an array to form a bit phase histogram. Spikes within the bit frequency and bit phase histograms can be used to determine whether the received signal stream includes FSK or PSK signals. An enhanced bit phase analysis can also used, if needed.