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We report results of stability and repeatability measurements performed on a selection of different noise sources for selected frequencies between 12 GHz and 26.5 GHz. Measurements cover intervals classified as intermediate term (about 1 week) and long term (about 1 year or more). Noise sources measured include a commercial diode source, a gas-discharge source constructed by NIST, a specially modified commercial diode source, and a variable-temperature FET-based source. All sources exhibit excellent stability, typically consistent with zero drift in noise temperature within the uncertainty of the tests.
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Randa et al. (2001) studied this question.
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