TABLE OF CONTENTS The earliest problem in electronic communications was to create receivers capable of detecting weak signals. Even with the invention of the vacuum tube, the difficulty of obtaining adequate gain at high frequencies limited the capabilities of receivers. Very soon, however, it became clear that electronic noise was the limiting factor in communications, and efforts were made to minimize both noise and its effects. These efforts continue into the present, even though extremely low-noise receivers can now be created. The goal of this book is to impart a comprehensive understanding of noise, its effect on systems, and methods for its analysis in both linear and nonlinear circuits.
Electronic noise is manifest as a randomly varying voltage or current. The defining characteristic of noise is its random nature. Although they are sometimes loosely called noise, deterministic signals, such as spurious signals, interference, and intermodulation distortion, are not noise and are outside the scope of this book. Here, we address only random noise.
In this book, we treat electronic noise as a stationary random process. That is, the noise voltage or current at any point in a circuit varies randomly, but with statistical characteristics that do not change with time. Station-arity is an assumption that may not always be warranted; however, in the great majority of cases it is entirely appropriate, and thus will be an underlying assumption throughout.
The noise that affects communication systems can be generated in the electronics...
