Question

In amplitude modulation, sinusoidal carrier frequency used is denoted by ${\omega }_c$ and the signal frequency is denoted by ${\omega }_m$. The bandwidth $\left(△{\omega }_m\right)$ of the signal is such that $△{\omega }_m<<{\omega }_c$. Which of the following frequencies is not contained in the modulated wave?

• A. ${\omega }_c-{\omega }_m$
• B. ${\omega }_m$
• C. ${\omega }_c$
• D. ${\omega }_m+{\omega }_c$

Answer 1

The correct option is B ${\omega }_m$

Here ${\omega }_c-{\omega }_m$ and ${\omega }_c-{\omega }_m$ are respectively called the lower side and upper side frequencies. The modulated signal consists of the carrier wave of frequency ${\omega }_c$ plus two sinusoidal waves each with a frequency slightly different from, known as side bands. The frequency spectrum of the amplitude modulated signal is shown in figure.

Hence we can say that the frequency which is transmitted is in between ${\omega }_c-{\omega }_m$ and ${\omega }_c-{\omega }_m$. Hence ${\omega }_m$ is not contained in the modulated wave.