Vertical slice through the dirty data cube, smoothed to an angular resolution of 30″, taken at RA = 23:38:14.65 covering 2 degrees in declination and the full bandwidth. Left: significant spectral ripples are clearly visible after subtracting the continuum model used for self-calibration, hampering faint source detection. Right: illustration of the effectiveness of subtracting an iteratively fitted spline function of order 15 from each spectrum, resulting in uniform noise. H I emission from a galaxy can be observed in the bottom-left quadrant of this position-velocity slice.