The frequency spectrum of an actual FM signal has components extending out to infinite frequency, although they become negligibly small beyond a point.

• 在模拟应用中，载波的频率跟随输入信号的幅度直接成等比例变化。在数字应用领域，载波的频率则根据数据序列的值作离散跳变，即所谓的频率键控。