In one embodiment a method for suppressing narrowband interference in an RF signal is provided. The method includes providing a block of baseband digital samples of the RF signal and computing n-1 stages of an n stage fast Fourier transform (FFT) on the block of the baseband digital samples to produce a first block of intermediate data points. A final threshold is computed based on values of the intermediate data points. A final stage of the n stage FFT is computed from the first block of intermediate data points to produce a block of output data points, and the output data points that have an energy above the final threshold are attenuated.