Chapter Overview
A sine wave carrier can be modulated by varying its amplitude, frequency, or phase shift. The basic equation for a carrier wave is
where Vc = peak amplitude, f = frequency, and θ = 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.
Chapter Outline
5-1 Basic Principles of Frequency Modulation
5-2 Principles of Phase Modulation
5-3 Modulation Index and Sidebands
5-4 Noise-Suppression Effects of FM
5-5 Frequency Modulation versus Amplitude
Chapter Objectives
- Compare and contrast frequency modulation and phase modulation.
- Calculate the modulation index given the maximum deviation and the maximum modulating frequency and use the modulation index and Bessel coefficients to determine the number of significant sidebands in an FM signal.
- Calculate the bandwidth of an FM signal by using two methods and explain the difference between the two.
- Explain how preemphasis is used to solve the problem of the interference of high-frequency components by noise.
- List the advantages and disadvantages of FM as compared to AM.
- Give the reasons for FM’s superior immunity to noise.