Question

(i) Draw the plot of amplitude versus ‘ω’ for an amplitude modulated wave whose carrier wave (ω_c) is carrying two modulating signals, ω₁ and ω₂ (ω₂ > ω₁). [Hint: Follow derivation from Eq 15.6 of NCERT Textbook of XII] 

(ii) Is the plot symmetrical about ω_c? Comment especially about plot in region ω < ω_c. 

(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 1

(i) Plot of amplitude versus w is shown in the Figure.

(ii) As can be seen, the frequency spectrum is not symmetrical about ω_c. Crowding of the spectrum is present for ω < ω_c. 

(iii) Adding more modulating signals lead to more crowding in ω < ω_c and more chances of mixing of signals. in 

(iv) Increase bandwidth and ω_c to accommodate more signals. This shows that large carrier frequency enables to carry more information (more ω_m) and which will in turn increase bandwidth.