Ringing

A problem is sometimes seen when Frequency Switching if there is a strong interference spike in the passband which does not switch out. This results in strong `ringing' in the subband containing the spike, because of the Natural weighting used in the Fourier Transform. It can be fixed by (i) Hanning smoothing the final spectrum in SPECX, (ii) Changing the default option for data reduction when loading the DAS or, (iii) Shifting the spectral line to a different subband (by changing the velocity, for example).