A sine wave carrier can be modulated by varying its amplitude, frequency, or phase shift. The basic equation for a carrier wave is

y Vc sin 1 2pft u2

where Vc peak amplitude, f frequency, and phase angle

Impressing an information signal on a carrier by changing its frequency produces FM. Varying the amount of phase shift that a carrier experiences is known as phase modulation (PM). Varying the phase shift of a carrier also produces FM. FM and PM are collectively referred to as angle modulation. Since FM is generally superior in performance to AM, it is widely used in many areas of communication electronics.