Overview

Noise is the most impertinent of all forms of interruptions. It is not only an interruption, but also a disruption of thought.

- Arthur Schopenhauer

He that loves noise must buy a pig.

- John Ray

The noise is so great, one cannot hear God thunder.

- R. C. Trench

5.1 Introduction

Many noise properties are statistical in nature. Thermal noise, also known as white or Gaussian noise, is the fundamental limit on the smallest signal a receiving system can process. In this chapter, we will examine noise from a mathematical point of view and relate this knowledge to receiving systems.

5.2 Equivalent Model for a RF Device

Figure 5-1 shows the general noise model that will be used throughout this chapter. The signal source can be a signal generator, antenna or another RF amplifier. We will model the signal source as a voltage source V _S in series with a resistor R _s. The resistor R _s represents the output impedance of the signal source. R _s can also be used to account for the noise present at the output port of the signal source. We will assume this resistor is at some noise temperature ( T _S). T _S is not the physical temperature of the signal source but accounts for the noise power present at the output of the signal source. Eventually, we will replace the source notation ( R _s and T _S) with an antenna notation...