Question

In amplitude modulation the bandwidth is

• A. equal to the signal frequency
• B. Twice the signal frequency
• C. Thrice the signal frequency
• D. Four times the signal frequency

Answer 1

The correct option is B

Twice the signal frequency

Frequency of amplitude

We know that ${\omega }_c$ is the carrier signal frequency and ${\omega }_m$ is the modulated frequency.

The lower side frequency of the amplitude wave is $\frac{{\omega }_c-{\omega }_m}{2}$

The upper side frequency of the amplitude wave is $\frac{{\omega }_c+{\omega }_m}{2}$

The signal frequency which is present in the side bands is $\frac{{\omega }_m}{2}$

Calculating bandwidth of the amplitude modulation

We know that the amplitude modulation bandwidth is defined as the difference between the upper and lower side frequencies of the amplitude-modulated pulse.

$$\begin{gathered} Bandwidth=\frac{{\omega }_c+{\omega }_m}{2}-\frac{{\omega }_c-{\omega }_m}{2} \\ Bandwidth=\frac{{\omega }_c+{\omega }_m-{\omega }_c+{\omega }_m}{2} \\ Bandwidth=2\frac{{\omega }_m}{2} \end{gathered}$$

Bandwidth is double the frequency of the transmission. As a result, the bandwidth in amplitude modulation is double the signal frequency.

Hence, option B is the correct answer.