3.5 Modulation Techniques  
  3.5.2 Basic modulation techniques  
As discussed earlier, a goal of communications is to use a carrier frequency as the basic frequency of a communication, but to modify it by using a process called modulation to encode information onto the carrier wave . 

There are three aspects of the basic carrier wave that can be modulated:

  1. Amplitude
  2. Frequency
  3. Phase or angle

The three corresponding techniques are as follows:

  1. Amplitude modulation (AM)
  2. Frequency modulation (FM)
  3. Phase modulation (PM)

Most communication systems use some form or combination of these three basic modulation techniques.

Extreme cases of these techniques include the following:

  • Amplitude shift keying (ASK) - Turning the amplitude all the way off
  • Frequency shift keying (FSK) - Hopping to an extreme frequency
  • Phase shift keying (PSK) - Shifting the phase 180 degrees

Use the interactive activity to see how a zero or a one can modulate an analog carrier signal, in each of these techniques.

 

 

Interactive Activity

Interactive Activity: Digital Modulation

This activity shows examples of digital modulation.