Technically, it is the temperature of a passive system having an available noise power per unit bandwidth equal to that of the actual terminals. The noise temperature of a simple resistor is the actual temperature of the resistor, while the noise temperature of another component could be many times the observed absolute temperature. Used in microwave communications and sometimes radar, it is the equivalent of noise figure expressed in Kelvins

(Te = 290 [log-1 (NF dB/10) -1]).