Here is the question: AM modulation Solution to b and d is also provided. NO NEE
ID: 2268577 • Letter: H
Question
Here is the question: AM modulation
Solution to b and d is also provided.
NO NEED TO SOLVE THE QUESTION. I just want to know why in part d: the method for calculating energy of the carrier and energy of the sidebands are different?
Further explanation for d would be also great.
Question-1: The message signal m(t) = sinc(t) is used to AM-modulate the carrier signal c(t) = 2 cos(2 ), with an amplitude sensitivity of ka-0.5. a) Formulate the AM signal, s(t). b) Draw s(t) in time. c) Draw the spectrum (FT of sCt) d) What percentage of the modulated signal's energy corresponds to the message? (Assume that almost all of the energy of the "sinc" function is contained in the interval of [-3,3] seconds, so the modulated signal is only transmitted during this period oftimeExplanation / Answer
AM wave has carrier (fc) and two side bands (fc+fm,fc-fm), that is the message signal frequency only present in side bands there is no message present in carrier signal.(just used as carrier of message signal)
energy efficiency= Esideband/total energy
= ma2 / 2+ ma2
for 100 percent modulation(modulation index ma=1)
=1/2+1
=0.33
=33%
that is only 33% energyis used for side bands and remaing 67% (wastage energy)is used for carrier,this is a major disadvantage of Amplitude Modulation
so energy of the carrier and energy of the sidebands are different.