A demonstration of Fourier domain excision of periodic RFI. Left panel: two intensity time sequences: the original sequence recorded at a radio telescope (black), the second half of which is evidently contaminated by periodic RFI, and the resultant sequence (red) when the strong frequency components in the Fourier transform of the original one are zapped. Both of the sequences were detrended for any slow variations before plotting. Right panel: normalized histograms for the two sequences shown on the left and the ±3.5σ bounds around the mean level marked as vertical lines, in the corresponding colors.