| the ratio of the total noise power appearing at the output of a given linear two port device within a specified frequency band, to the portion of this power originating from the one-port device connected to the input of the two port device, the noise temperature of the one-port device being assumed equal at all frequencies to the reference thermodynamic temperature conventionally fixed around 290 K
NOTE 1 – The mean noise factor is related to the mean noise temperature T as follows:
where T0 is the reference thermodynamic temperature.
NOTE 2 – The value of the mean noise factor may be expressed in decibels. 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.