This is Episode 3, Part 2, but is optional, so it is placed in the Radio Design 101 video series as Appendix A. The material here is not required for design and construction of our FM radio receiver. Rather, it is provided for those who want more background in the analysis of small signal RF amplifiers, and the operation of transistors used in their design. We review Episode 3 (Part 1), and then show how BJT transistors are created and how they are modeled. The goal is to provide a broader foundation for those interested in different amplifier types (such as common-emitter and cascode), and in the underlying mathematics from which gains, input and output impedances, and operating frequency limitations can be understood.