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 sideband frequencies are 1506 kHz and 1494 kHz (b) The bandwidth required for amplitude modulation is 6kHz (c) The bandwidth required for amplitude modulation is 3 MHz (d) The sideband frequencies are 1503 kHz and 1497 kHz.
Correct options are B) and D) Side band frequencies: The AM wave contains three frequencies fc,(fc+fm) and (fc−fm) where fc is called carrier frequency, (fc+fm) and (fc−fm) are called side band frequencies. (fc+fm): is upper side band (USB) frequency (fc−fm): is the lower side band (LSB) frequency Side band frequencies are generally close to carrier frequency. According to the given criteria, frequency of audio sine wave fm=3kHz and frequency of carrier signal fc=1.5MHz=1500kHz Now, side band frequencies is fc±fm=(1500±3) =1503kHz,1497kHz Upper side Band frequency is 1503kHz and Lower side band frequency is 1497kHz Also bandwidth is 2fm=2×3=6kHz
