Question

[15 points] You are asked to design a DSB-SC AM modulator to generate a modulated signal km(t)cos(wt+0), where m(t) is a signal band-limited to B Hz. The following figure shows a DSB- SC AM modulator available in the stockroom. The carrier generator available generates not cos(wct), but cos (wct). Explain whether you would be able to generate the desired signal using only this equipment. You may use any kind of filter you like. 3. What kind of filter is required in Figure 2-a)? Specify the filter type (LPF, BPF, BSF, etc.) and bandwidth. Explain why the filter you specified works. a. b. Determine the signal spectra at points b and c, and indicate the frequency bands occupied by these spectra. c. What is the minimum usable value of wc? M(f) km(t) cos t Filter_ -B 0 cos3 o Figure 2: A DSB-SC AM Modulator and the Spectrum of m(t)

Answer 1

go, fc

mlt). Cos 3uct Co SpecH Auo) at point (b) Lomiuca hy ofe

So, 0 Spectg um at pointƠ C-T

Answer 2

a DSBSC wave  is given as:                                                                       

       S(t)=20Cos(8000πt)+20Cos(4000πt)  given that  Ac=20

      Write the expression  for the carrier and modulating  signal   c(t) and m(t)