A method is disclosed for triggering upon signal events occurring in frequency domain signals. The method includes repeatedly sampling a time-varying signal and generating a plurality of digital frequency domain spectrums based on the samples of the time-varying signal. A frequency domain bitmap for the time-varying signal is repeatedly updated via application of the digital frequency domain spectrums. The method further includes selecting a portion of the frequency domain bitmap, determining a signal occupancy in the selected portion, and triggering a capture of the time-varying signal based on and in response to the occupancy determination for the selected portion of the bitmap.