Control and Measurement of Unintentional Electromagnetic Radiation

CHAPTER 4

FREQUENCY DOMAIN DESCRIPTIONS OF PERIODIC VOLTAGES

4.1 INTRODUCTION

Effective control of unintentional electromagnetic radiations can be greatly facilitated when the radiations are usefully characterized. As previously noted, regulatory limits on unintentional radiations are limits on the amplitudes of their sinusoidal components, and, to verify compliance with the limits, the amplitudes of those sinusoidal components are measured. As a result, useful descriptions associate the amplitudes and frequencies of the sinusoidal components of unintentional radiations with voltage and current parameters that are either well known or easily evaluated.

In addition, electromagnetic radiations are the direct result of time-varying electric currents, and currents are sometimes difficult to observe and evaluate. However, currents are established by voltages, which are usually relatively easy to observe and evaluate with an oscilloscope. Therefore, a good start toward obtaining useful descriptions of unnecessary electromagnetic radiations is to describe time-varying voltages in terms of their sinusoidal components. Then, the currents caused by those voltages and the radiations caused by the currents can be similarly described. Given these frequency-domain descriptions, or sinusoidal component lists, the causes of the radiations can be better understood, and the radiations can be better controlled.

The objective in this chapter, then, is to provide relatively simple methods for describing ...