FM broadcast

A typical spectrum of an analog-only FM broadcast station, averaged over approximately one minute. The station was playing music during this period. Below is a dynamic spectrum of another FM broadcast station, which was broadcasting only voice. During pauses in the speaker's voice, the FM signal is heavily concentrated in discrete sidebands, which are a result of the 19 kHz pilot tone injected to demarcate various components of the signal, including left+right and left-right stereo channel components. When talking, the varying amplitude of the speaker's voice causes the signal to spread in frequency by a proportional amount.