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Home Electrical and Electronics Digital Communication Analyze Pulse Amplitude Modulation (PAM).
Digital Communication Lab Experiments

Analyze Pulse Amplitude Modulation (PAM).



Objective:

Analyze Pulse Amplitude Modulation (PAM).

Apparatus Required:

  1. Pulse Amplitude Modulation Kit
  2. Cathode Ray Oscilloscope (CRO)
  3. Binary Data Generator
  4. Power supply
  5. Patch cords

Theory

In Pulse Amplitude Modulation (PAM) message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitude of train of carrier pulses is varied according to the sample value of the message signal. A train of very short pulses of constant amplitude and fast repetition rate is chosen the amplitude of these pulse is made to vary in accordance with that of a slower modulating signal the result is that of multiplying the train by the modulating signal the envelope of the pulse height corresponds to the modulating wave The PAM wave contain upper and lower side band frequencies besides the modulating and pulse signals. Figure 3.1 (a) shows the waveforms for message signal (b) shows the carrier pulse train and (c) shows the PAM signal.

(a)mesage-signal(b)carrier-signal(c)pam-signal

Procedure:-

  1. Make the circuit as shown in figure 3.2.
  2. Make the circuit as shown in figure 3.2.
  3. Set the pulse generator output to be 2Vpp at 8 Khz.
  4. The sampled and reconstructed waveforms are measured using CRO.
  5. Repeat for different frequency of pulse generator.
  6. pam-trainer-kit

Observation:The different output waveforms shown in figures 3.3 to 3.6 are observed with the help of CRO and are traced with the help of graph paper.

modulating-signal
carrier-signal(16khz)-and-pulse-amplitude-modulated-signal
carrier-signal(32khz)-and-pulse-amplitude-modulated-signal
carrier-signal(64khz)-and-pulse-amplitude-modulated-signal

Conclusion:The study of pulse amplitude modulation using switching method and by sample and hold circuit has been successfully done.

Questions:

  1. What is Pulse Amplitude modulation?
  2. Why PAM is not preferable in digital transmission?
  3. Explain in brief sample and hold method.
  4. Write the advantages and disadvantages of PAM.

Precautions:

  1. Check the connections before giving the supply.
  2. Observations should be done carefully.