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Introduction to FM

The general sinusoidal modulated FM signal is defined by:

Modulation Index

The FM modulation index is defined as the ratio of carrier deviation to modulation frequency:

As a result, the FM equation is generally written as:

FM generates an infinite number of side frequencies each of which is an integer multiple of the modulation signal frequency. Besselís functions are used to calculate their amplitude.

A plot of the amplitudes of the carrier and first five side frequencies as a function of modulation index resembles: