English: NASA-created illustration of the Wilkinson Microwave Anisotropy Probe spacecraft receivers. "WMAP's Microwave System consists of ten 4-channel “differencing assemblies”, each of which receives signals from a pair of feeds. The output of each assembly is proportional to the temperature (brightness) difference between the two lines of sight on the sky. To improve sensitivity and stability the system has a cold section where the first stages of microwave signal amplification occur, then a warm section where the remaining amplification occurs before being converted to an electrical signal."