RSMS - Calibration References
2 Many references do not offer a clear explanation of the difference between noise factor and excess noise ratio. Noise factor is the ratio of noise power from a device and thermal noise (ndevice/kTB). The excess noise ratio is equal to the noise factor minus one, making it the fraction of power above (in excess of ) kTB. The noise figure of a system is defined as 10 log of the noise factor, forcing a solution for noise factor in the calculations. However, since many noise sources are specified in terms of excess noise ratio, that quantity must sometimes be used.