[SOLVED] EE352 - Lab 3 - Conventional Amplitude Modulation

Description

  Labwork (Conventional Amplitude Modulation/Demodulation)

3.1     Preliminaries

In order to modulate a message signal with conventional AM, first multiply the message signal m(t) with modulation factor k_a. Then, add to this signal one. After the addition of one, multiply this signal with a carrier signal c(t) = A_ccos(2πf_ct) to obtain the modulated signal.

Figure 1: Modulation of Conventional AM

In order to demodulate this signal, first, take the square of the modulated signal. Then, filter this squared signal with a low pass filter (LPF). After taking the square root of the filtered signal, reach an estimate of the message signal. This technique is called Square-Law detector.

Figure 2: Demodulation of Conventional AM

3.2       Conventional Amplitude Modulation

• Obtain the time vector with the duration of t = 0.1 seconds and with the sampling frequency of F_s = 10000 Hz.
• Generate a carrier signal c(t) = A_ccos(2πf_ct) and a message signal m(t) = A_mcos(2πf_mt) where A_m = A_c = 1 and f_m = 100 Hz and f_c = 1000 Hz with respect to time vector obtained in (a).
• Obtain the modulated signal, s(t).
• Plot the modulated signal s(t) for three modulation factors namely 0.5,1 and 2 in the same figure by using subplot.
• Comment on the effects of the modulation factors.
• Plot the magnitude of the frequency responses of m(t),c(t) and s(t) for k_a = 0.5 in the same figure by using subplot.

3.3       Conventional AM Demodulation

• Demodulate the modulated signal s(t) when k_a = 0.9 and k_a = 2 by following the steps given in the preliminaries. Hint: You can use butter(.) with the suitable filter order and cut off frequency and filter(.)
• Comment on your choice of the filter order and the cut off frequency.
• Plot the demodulated signals in the same figure by using subplot.
• Comment on the the results that you obtain in (c).