Zk50group03

INTRODUCTION
Frequency modulation (FM) is variation of the frequency of a carrier wave,commonly a radio wave in accordance with variations in the audio signal being sent. Developed by American electrical engineer Edwin H. Armstrong in the early 1930s, FM is less susceptible to outside interference and noise example of FM such as thunderstorms and nearby machinery. Such noise generally affects the amplitude of a radio wave but not its frequency, so an FM signal remains virtually unchanged. FM is also better able to transmit sounds in stereo than AM. Commercial FM broadcasting stations transmit their signals in the frequency range of 88 megahertz (MHz) to 108 MHz.Analog applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input signal amplitude. Digital data can be sent by shifting the carrier's frequency among a set of discrete values, a technique known as frequency-shift keying. Frequency modulation can be regarded as phase modulation where the carrier phase modulation is the time integral of the FM modulating signal.FM is widely used for broadcasting of music and speech, and in two-way radio systems, in magnetic tape recording systems, and certain video transmission systems. In radio systems, frequency modulation with sufficient bandwidth provides an advantage in cancelling naturally-occurring noise.

CONTENT
Frequency spectrum of an FM wave
The spectrum of an FM wave is complex mathematically. It consists of a carrier wave with a (theoretically infinite) series of pairs of sidebands. The amplitude of the carrier and each pair of sidebands is given by Bessel functions. Bessel function values for the carrier and first 5 sidebands (but realise that it is an infinite series of sidebands. the amplitude of the higher sidebands is very low at low modulation indexes and can be ignored).

Carson's rule
Carson's rule is often used to estimate the occupied bandwidth of an FM signal. Carson's rule estimates the bandwidth as twice the sum of the peak deviation and the highest modulating frequency.
BW=2×(D_max+ F_(max ))
where:
Dmax = peak frequency deviation
Fmax = highest modulating frequency

APPLICATION OF FM SIGNAL