This Topic considers how to plot the Spectrum of a periodic signal, by plotting the complex Fourier coefficient against frequency of the corresponding complex phasor. This Topic considers a very common example, the spectrum of a periodic pulse sequence. First, the complex Fourier coefficients are calculated, and it is shown that these can be written as a so-called sinc function. The video shows how to plot the sinc function, including what happens at the origin, and when the function intersects the independent variable axis. This enables the complex Fourier coefficients of the periodic pulse signal to be plotted against frequency. The video finishes by showing how to plot magnitude and phase of these coefficients separately, while meeting the conjugate symmetry constraints of the complex Fourier coefficient.