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The paper deals with a spectroscopic method intended for characterization of virgin oxide and resin-coated cold emission cathodes. The noise spectroscopy in time and frequency domain is based on measuring cathode's voltage noise, in ultrahigh vacuum conditions ~2 · 10-5 Pa. These conditions are required in order to avoid environment interaction with ions, which are present in the vacuum chamber, and also to reduce the influence of the electron-induced desorption and adsorption, which poses one of the significant noise sources. For these experiments, cold cathode with epoxy-resin coating was prepared. A comprehensive investigation was carried out to determine particular noise sources and to compare clean cathodes with the resin-coated one, in order to describe influence of the oxide and dielectric epoxy layer on to the emission current stability. Spectra obtained, for various emission currents at different voltages, are described and explained. The results suggest that the resin-layer changes cathode performance and extends its durability.