Question

Write two basic modes of communication. Explain the process of amplitude modulation. Draw a schematic sketch showing how amplitude modulated signal is obtained by superposing a modulating signal over a sinusoidal carrier wave.

Answer 1

The two basic modes of communication are :

(1) Point-to-point communication

(2) Broadcast communication.

Amplitude Modulation: Amplitude modulation is obtained by changing the amplitude of the carrier waves according to the amplitude of the modulating wave.

Let the modulating signal be $m\left(t\right)=A_{m}sin{\omega }_{m}t$,

Where ${\omega }_m=2\pi f_m$ is the angular frequency of the message signal.

Modulated signal $C_m\left(t\right)$ is

$C_m\left(t\right)=(A_c+A_{m}sin{\omega }_{m}t)sin{\omega }_{c}t$

= $A_c(1+\frac{A_m}{A_c}sin{\omega }_{m}t)sin{\omega }_{c}t$

$\therefore C_m\left(t\right)=A_{c}sin{\omega }_{c}t+\mu A_{c}sin{\omega }_{m}tsin{\omega }_{c}t$

where $\mu =\frac{A_m}{A_c}$ is the modulation index.

$C_m\left(t\right)=A_{c}sin{\omega }_{c}t+\frac{\mu A_c}{2}cos({\omega }_c-{\omega }_m)t-\frac{\mu A_c}{2}cos({\omega }_c+{\omega }_m)t$

${\omega }_c-{\omega }_m$and ${\omega }_c+{\omega }_m$ are the lower side and upper side frequencies, respectively.

Production of amplitude modulated wave :


Amplitude modulated signal is obtained by superposing a modulating signal over a sinusoidal carrier wave.