Question

Sinusoidal carrier voltage of frequency \(1.5\,MHz\) and amplitude \(50\,V\) is amplitude modulated by a sinusoidal voltage of frequency \(10\,kHz\) producing \(50%\) modulation. Frequencies in lower and upper side-band are

• A. 1490, 1510
• B. 1510, 1490
• C. \( \dfrac{1}{1490},\ \dfrac{1}{1510} \)
• D. \( \dfrac{1}{1510},\ \dfrac{1}{1490} \)

Hint:

In AM, sidebands are always \(f_c \pm f_m\). Modulation index changes amplitude, not sideband frequencies.

Answer 1

The Correct Option is A

Step 1: Recall AM sideband frequencies.
In amplitude modulation, sideband frequencies are:
\[ f_{LSB} = f_c - f_m,\quad f_{USB} = f_c + f_m \] Step 2: Substitute given values.
Carrier frequency:
\[ f_c = 1.5\,MHz = 1500\,kHz \] Modulating frequency:
\[ f_m = 10\,kHz \] Step 3: Calculate sidebands.
\[ f_{LSB} = 1500 - 10 = 1490\,kHz \] \[ f_{USB} = 1500 + 10 = 1510\,kHz \] Final Answer: \[ \boxed{1490\,kHz,\ 1510\,kHz} \]