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 ${\omega }_c$, 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.