Experiment 2 : DSB-SC Modulation and Demodulation

Objective: DSB-SC Modulation and Demodulation

Description: In this experiment you will design an analog modulator and an analog demodulator. Both simple multiplier type and nonlinear element type Modulators/Demodulators will be constructed. You will compare the received signal with the transmitted signal and also study the effect of phase shift at the demodulator.

The carrier frequency will be 500kHz, which is in the commercial AM radio frequency range. The signal bandwidth will be 20kHz, which is the bandwidth needed for high quality music. (Actual systems may use a smaller bandwidth.)



  1. Write the equations relating m(t), s(t), v(t). in II. (that is write the other two in terms of m(t) ) Verify your simulation results. You do not need to submit any plots for this part.
  2. Submit a block diagram of II.
  3. Submit a block diagram of III. Label any ambiguous components.
  4. Write the equations relating m(t), s(t), v(t) in III. Your equations should explain the working of the demodulator.
  5. Give plots of both m(t) and v(t) for III. Also give plots of the Fourier transforms of m(t), s(t) and v(t).
  6. Explain with equations the phase-attenuation plot obtained in IV. Submit this plot.
  7. Print the Fourier transform of the demodulated signal of part IV when phase shift is pi/2. Do you see anything unusual? Explain what you see.
  8. Using the setup of part IV, and phase offset zero, show the transmitted signal with a solid line and the received one with a dashed line on the same plot. See scope for details. Comment on the delay between the two signals. Extra credit - Can you justify the value of this delay?

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