Abstract: A system is disclosed for analyzing in real time the frequency spectrum of an incoming signal of unknown frequency characteristics. This is accomplished by first generating a train of sampling pulses in repetitive frames, where each frame of pulses represents a series of cross-correlation functions in terms of a predetermined number of sampling intervals and a predetermined number of harmonics. These sampling pulses are then multiplied with the incoming signal to generate a train of discrete sampled outputs. The discrete sampled outputs from the multiplying means are accumulated in an accumulator and a frequency domain output signal is produced for each frame of sampling pulses.