A measure of the noise power density at the output of a radio or radar receiver due to internally generated noise and passive losses in the receiver. In particular, the receiver temperature T_r is the temperature of a resistor having noise power per unit bandwidth equal to that of the receiver output at a given frequency. It is given in terms of the power output P and bandwidth B of the receiver by T_r = P/kB, where k denotes Boltzmann's constant, 1. 38 × 10⁻²³J K⁻¹. The receiver temperature is related to the receiver noise factor F by T_r = T_o(F − 1) with T_o = 290 K. See noise temperature, noise figure.