ratio of the available power spectral density of the noise appearing at a given frequency at the output of a given linear two-port device, to the spectral density which would be present at the output if the only source of noise were the thermal noise due to a one-port device connected to the input and which is assumed to have at all frequencies a spot noise temperature equal to the reference thermodynamic temperature fixed by convention at around 290 K Note 1 to entry: The spot noise factor F(f) of a linear two-port device is related to the equivalent spot noise temperature T(f) as follows: where T0 is the thermodynamic reference temperature. Note 2 to entry: In English, the term “noise factor” is generally employed when the ratio is expressed arithmetically, and “noise figure” is employed when the ratio is expressed in decibels.
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