JEE Main2017PhysicsCommunication SystemActual
A signal of frequency 20 kHz and peak voltage of 5 Volt is used to modulate a carrier wave of frequency 1 . 2 MHz and peak voltage 25 Volts . Choose the correct statement.
Options
- AModulation index = 5 , side frequency bands are at 1400   kHz   and   1000   kHz .
- BModulation index = 5 , side frequency bands are at 21 . 2   kHz   and   18 . 8   kHz .
- CModulation index = 0 . 2 , side frequency bands are at 1220   kHz   and   1180   kHz .
- DModulation index = 5 , side frequency bands are at 24 . 2   kHz   and   18 . 8   kHz .
Correct answer
C. Modulation index = 0 . 2 , side frequency bands are at 1220   kHz   and   1180   kHz .
Step-by-step solution
Modulation index defines the modulated signal's ratio of maximum to minimum voltage = V m V c = 5 25 = 0.2 Carrier Frequency 1.2 × 10 3   kHz f c = 1200   kHz . Lower side-band frequency, f 1 = 1200 - 20 = 1180   KHz . Upper band frequency, f 2   = 1200 + 20 = 1220   KHz   .