Question

Audio sine waves of $3 \,kHz$ frequency are used to amplitude modulate a carrier signal of $1.5 \,MHz$. Which of the following statements are true?

• A. The side band frequencies are 1506 kHz and 1494 kHz
• B. The bandwidth required for amplitude modulation is 6 kHz
• C. The bandwidth required for amplitude modulation is 3 MHz
• D. The side band frequencies are 1503 kHz and 1497 kHz

Answer 1

Answer: (B), (D)

$\omega_{m}=3\, kHz , \omega_{ c }=1.5 \,MHz =1500 \,kHz$
Side band frequencies $=\left(\omega_{c}-\omega_{m}\right)$ and $\left(\omega_{c}+\omega_{m}\right)$
$=(1500-3) \,kHz$ and $(1500+3) \,kHz$
$=1497 \,kHz$ and $1503 \,Hz$
Bandwidth $=2 \omega_{m}=2 \times 3=6 \,kHz$