question_answer 37)

   (i) Draw the plot of amplitude versus '' for an amplitude modulated wave whose carrier wave () is carrying two modulating signals,  [Hint: Follow derivation from Eq 15.6 of NCERT Textbook of XII i.e., Eq. 15 of Unit 10 of Fundamental Physics Vol. ] (ii) Is the plot symmetrical about? Comment especially about plot in region (iii) Extrapolate and predict the problems one can expect if more waves are to be modulated. (iv) Suggest solutions to the above problem. In the process can one understand another advantage of modulation in terms of bandwidth?

Answer:

                  (i)  Let the two modulating signals be superimposed on carrier signal  The signal produced is To produce amplitude modulated wave the signal x(t) is passed through a square law device which produces an output given by In the above amplitude modulated waves, the frequencies present are The plot of amplitude versus co is shown in Fig. 10(EP).7. (ii) From Pig. 10(EP).7, we note that frequency spectrum is not symmetrical about  Crowding of spectrum is present for    (Oy («'0 If more waves are to be modulated then there will be more crowding in the modulating signal in the region . That will result more chances of mixing of signals. (iv) To accommodate more signals, we should increase band width and frequency of carrier waves . This shows that large carrier frequency enables to carry more information (i.e., more ) and the same will intum increase band width.