How are FM signal generated?

There are several methods for generating FM signals but they all basically involve an oscillator with an electrically adjustable frequency. This type of oscillator uses an input voltage to affect the frequency of its output. For example, when the applied voltage increases, the oscillator output frequency increases and when the applied voltage decreases, the oscillator output frequency decreases as well. If no voltage is applied to the oscillator its output will be a signal at its centre frequency. The amount of frequency variations is deviated around the oscillators' centre frequency.