This is the noise model of a receiving antenna, where all of the noisy units have been replaced by one noiseless amplifier with a single noise source Ts as its input. Calculate the system noise temperature Ts after entering Tin (noise temperature of the antenna), Trf (noise temp. of RF amplifier), Tif (noise temp. of IF amp), Tm (noise temp. of mixer...all in deg. K), then Grf & Gm (gains of RF amp and mixer, both in dB). As the first example, use Tin = 25, Trf = 50, Tif = 1000, Tm = 500, Grf = 23 & Gm = 0. Press the "Calculate" button and your result should be 82.5 K.

For example 2 change Gm to -10 and the result should be 127.5.