Frequency Domain Measurements

Theoretically, the transformation from the time domain (TD) to the frequency domain (FD) does not involve any loss of information of the signal, but only a different representation of it. Depending on the application, the analysis of a signal in FD may be more useful for the characterization of signals and devices, since it separates the different components of the signal. The instruments that are typically used for measurements in FD are spectrum analyzers (SAs) or, alternatively, the fast Fourier transform (FFT) algorithm of digitized time-domain signals. This chapter begins with a brief overview of the theoretical background on spectral analysis and on the measurement instruments operating in the frequency domain. Then several educational laboratory experiments are described that use spectral analysis with analog and digital approaches for characterizing signals, for assessing aliasing, for quantifying the harmonic distortion and the signal-to-noise ratio, for measurements on modulated signals, etc