21.1 Introduction

Spectrum analysis is a quick method to observe and measure signal levels and signal distortions. The display gives the user a visual representation of the magnitude of the Fourier transform of the input signals. The Fourier transform maps the time domain signal into the frequency domain as a set of sines and cosines. The measurement range of the signal analyzer is extremely large, exceeding 140 dB. These abilities make the spectrum analyzer a versatile instrument specially suited for the modern communications era. Spectrum analysis is essentially the examination of amplitude vs. frequency of a given signal source, antenna, or signal distribution system. This analysis can yield important information about the signals such as stability, distortion, amplitude, and types and quality of modulation. With this information, circuit or system adjustments may be made to increase efficiency or verify compliance to the many emerging regulations regarding both desired emissions and undesired emissions.

The modern spectrum analyzer has found many complex uses ranging from the R&D lab to manufacturing and field service. The signal analyzer has been a laboratory instrument of great value. The quick ability to view wide spectrum widths and then quickly zoom in to closely examine signals of interest has been highly valued by the R&D engineer. In the manufacturing area, the speed of measurements combined with the ability to access these data through computers has allowed very complex measurements to be made quickly, accurately, and repeatably.