In Chapter 8, we introduced noise and noise figure in mathematical terms. In this chapter, we will show how this information applies to transistor amplifiers. Two-port S-parameters and noise characteristics are published by microwave manufacturers to ensure that the transistor can be easily utilized in an amplifier design. We have introduced a mathematical representation of noise created by a two-port. The noise added by the two-port is characterized by a few quantities that are essential to the two-port and the input reflection coefficient. Some transistor data sheets show noise parameters for a particular transistor at several frequencies.