Noise figure meters measure the noise contribution of an amplifier relative to a noise-free amplifier at a reference temperature. For most Ku-band amplifiers, values are expressed in decibels (dB). Noise figure is defined as the ratio of the signal-to-noise (S/N) power ratio at the input to the S/N ratio at the output. It is independent of modulation and demodulation, and is not related to gain. Like sensitivity and bit error ratio (BER), however, noise figure is an important system parameter for receivers that process low-level signals. By determining the noise figure, the sensitivity of the bandwidth can then be estimated. Noise figure meters are used to test entire systems, or to test individual components such as the pre-amplifier, intermediate frequency (IF) amplifier, and mixer.