NEET Questions Solved

BOARD

(a) How is amplitutde modulation achieved?

(b) The frequencies of two side bands in an AM wave are 640 kHz and

660kHz respectively. Find the frequencies of carrier and modulating 

signal. What is the bandwidth required for amplitude modulation?            (3 marks)

(a) Amplitude modulation can be achieved by applying the 

message signal, and the carrier wave, to a non linear

(square law device) followed by a band pass filter.

(Alternatively, The student may just draw the block diagram.)

(Alternatively, Amplitude modulation is achieved by superposing a message

signal on a carrier wave in a way that causes the amplitude of the carrier

wave to change in accordance with the message signal.)                        (1 mark)

(b) Frequencies of side bands are:                                                     

               (vc+vm) and (vc-vm)                                                           (1/2 mark)

so,       vc+vm=660kHz

and        vc-vm=640kHz

so,        vc=650 kHz                                                                         (1/2 mark)

so,       vm=10 kHz                                                                            (1/2 mark)

Bandwidth = (660-640)kHz = 20kHz                                                        (1/2 mark)

 

 

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