Question

The frequencies of two side bands in an AM wave are $640\text{kHz}$ and $660\text{kHz}$ respectively. Find the frequencies of carrier and modulating signal. What is the bandwidth required for amplitude modulation

• A. $660\text{kHz},10\text{kHz},30\text{kHz}$
• B. $650\text{kHz},10\text{kHz},20\text{kHz}$
• C. $640\text{kHz},20\text{kHz},200\text{kHz}$
• D. $650\text{kHz},20\text{kHz},2\text{kHz}$

Answer 1

The correct option is B

$650\text{kHz},10\text{kHz},20\text{kHz}$

Frequency of carrier signal can be found as

$f_c=\frac{640+660}{2}=650\text{kHz}$

Frequency of modulated signal can be calculated as

$f_c+f_m=660\Rightarrow f_m=10\text{kHz}$

Now the band width of AM

$=(660-640)\text{kHz}=20\text{kHz}$