Introduction to Data Communications
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27. Modulation Techniques

Modulation techniques are methods used to encode digital information in an analog world. The 3 basic modulation techniques are:

AM (amplitude modulation)
FM (frequency modulation)
PM (phase modulation)

All 3 modulation techniques employ a carrier signal. A carrier signal is a single frequency that is used to carry the intelligence (data). For digital, the intelligence is either a 1 or 0. When we modulate the carrier , we are changing its characteristics to correspond to either a 1 or 0.

27a. AM - Amplitude Modulation

Amplitude Modulation modifies the amplitude of the carrier to represent 1s or 0s. In the above example, a 1 is represented by the presence of the carrier for a predefined period of 3 cycles of carrier. Absence or no carrier indicates a 0.

Advantages:

Simple to design.

Disadvantages:

Noise spikes on transmission medium interfere with the carrier signal.
Loss of connection is read as 0s.

Introduction to Data Communications
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