In an accepted method of measuring D region electron density with a rocket-borne DC-mode Langmuir probe, the resulting fine-structure signal is modified by a high-pass filter. While this form of data has been successfully used for power spectral analysis, it fails to reveal important spatial domain features without further processing. We demonstrate that the broadband signal can be recovered by use of a digital filter that corrects for the on-board high-pass filter effects. The D region broadband structure so recovered for a daytime equatorial flight shows variations in electron density consistent with a model of Kelvin-Helmholtz billows, and not consistent with inertial range turbulence. The isolated regions of irregularity are ~100 m thick near an altitude of 75 km, imbedded in a region with a staircase-structure electron density profile with ~200-m steps. We show suggestive similarities to a numerical model of KHI and to undersea observations of KHI-caused microstructure. ¿1991 American Geophysical Union