Page "Frequency modulation" Paragraph 9

While most of the energy of the signal is contained within f < sub > c </ sub > ± f < sub > Δ </ sub >, it can be shown by Fourier analysis that a wider range of frequencies is required to precisely represent an FM signal.

The frequency spectrum of an actual FM signal has components extending infinitely, although their amplitude decreases and higher-order components are often neglected in practical design problems.