Question

A modu action frequency an AM radio station is $250\text{kHz}$, which is $10\%$ of the carrier wave. If another AM station approaches you for license, what broadcast frequency will you allot ?

• A. $2750\text{kHz}$
• B. $2900\text{kHz}$
• C. $2250\text{kHz}$
• D. $2000\text{kHz}$

Answer 1

The correct option is D $2000\text{kHz}$

According to question, modulation frequency, $250\text{kHz}$ is $10\%$ of carrier wave
$f_{carrier}=\frac{250}{0.1}=2500\text{kHz}$

$\therefore$Range of signal $2500\pm 250\text{kHz}=2250\text{kHz}\text{to}2750\text{kHz}\text{for}2000\text{kHz}$
We cannot allot this frequency as waves can overlap in this range.

Now, if $f_c=2000\text{kHz},$ $f_{mod}=200Hz$
$\therefore \text{Range}=1800\text{kHz}\text{to}2200\text{kHz}$.

Hence required frequency is $2000\text{kHz}$