Frequency modulation is a form of modulation in which instantaneous frequency of carrier is varied in direct proportion to the amplitude of the message signal. Mathematically, it can be written as

where kf is the frequency deviation constant and  is the message signal. Thus, instantaneous frequency in FM is given by

Figure 1 shows a segment of speech signal, the un-modulated carrier signal and the corresponding frequency modulated signal.

Figure 1: Frequency Modulation

At the end of this experiment, students are encouraged to carry out practical observations by varying frequency deviation and carrier frequency.