What is a spectrum in signal?

Frequency spectrum of a signal is the range of frequencies contained by a signal. For example, a square wave is shown in Fig. 3.5A. It can be represented by a series of sine waves, S(t) = 4A/π sin(2πft) + 4A/3π sin(2π(3f)t) + 4A/5π sin(2π(5f)t + …)

The spectrum of a signal is the range of frequencies contained in the signal. The bandwidth is the difference between the lowest and highest frequency in the spectrum . It is therefore the width of the spectrum and is a measure of the information carrying capacity of the signal.

The signal spectrum describes a signal’s magnitude and phase characteristics as a function of frequency . The system spectrum describes how the system changes signal magnitude and phase as a function of frequency. For example, Figure 6.6 shows the magnitude and phase spectra of some hypothetical system.