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The basic characteristics of parametric amplifiers are reviewed briefly, with particular emphasis on the limitations on low-noise performance resulting from diode losses. Normalized curves showing the minimum excess temperature of a parametric amplifier for various spectrum arrangements are presented, where the normalizing factor is the degenerate-mode gain cutoff frequency. Experimental evidence consisting of noise figure measurements on an X-band amplifier is used to relate this cutoff frequency to an easily and commonly measured diode quality factor. Design considerations for a hypothetical L-band parametric amplifier are discussed to illustrate the implications of the noise analysis.