Angle Modulation

Phase modulation (PM) is a modulation pattern for conditioning communication signals for transmission. It encodes a message signal as variations in the instantaneous phase of a carrier wave. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. 

Frequency modulation (FM) is a type of angle modulation in which the frequency of a sinusoidal carrier wave deviates from a center frequency by an amount proportional to the instantaneous value of the message signal. In FM, the center frequency is the carrier frequency. 

A narrow band FM is the FM wave with a small bandwidth , The modulation index mf of narrow band FM is small as compared to one radian . Hence, the spectrum of narrow band FM consists of the carrier and upper sideband and a lower sideband . 

The modulation technique used here is wideband frequency modulation. When the highest frequency component of a modulating signal is greater than the peak frequency deviation of modulated signal , then it is called as wide band frequency modulation