For each of the following baseband signals (i) m(t) = cos 1000t, (ii) m(t) = 2cos 1000t + cos 2000t, and (iii) m(t) = cos 1000t cos 3000t:
a. Sketch the spectrum of m(t).
b. Sketch the spectrum of the DSB-SC signal m(t) cos 10,000t.
c. Identify the upper sideband (USB) and the lower sideband (LSB) spectra.
d. Identify the frequencies in the baseband, and the corresponding frequencies in the DSBSC, USB, and LSB spectra. Explain the nature of frequency shifting in each case.