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The paper presents the noise characteristics of microscopic cathode based on Schottky field emission. Schottky emission is considered to be the predominant electron source technology in actual focused electron beam equipment. For the ideal electron source, it is necessary to achieve following properties: small source size, low electron emission energy spread, angular intensity (an emission current per unit solid angle), low noise, long-term stability and a simple and low-cost operation. The noise spectroscopy in time and frequency domain is based on measuring cathode's voltage noise density in ultra-high vacuum conditions (UHV) in order to avoid environment interaction with ions which are present in the vacuum chamber. The first part of the article describes basic concept of electronic noise together with the description of used cathodes. Second part focuses on the method of measurement and in the last part, reached results are presented together with suitable explanation according to the concept of electronic noise.