Modulation:
  • It is the process of mixing a low energy message signal with the high energy carrier signal to produce a new high energy signal which carries information to a long distance.
  • A device that performs modulation is called modulator.
   How the modulation done?
   
    Types of signals in modulation:
    - Message signal
    - Carrier signal
    - Modulated signal
  • Message signal: The signal which contains a message to be transmitted to the destination is called a message signal. The message signal is also known as a modulating signal or baseband signal.
  • Carrier signal: The high energy or high frequency signal which has characteristics like amplitude, frequency, and phase but contains no information is called a carrier signal.
  • Modulated signal: When the message signal is mixed with the carrier signal, a new signal is produced. This new signal is known as a modulated signal.
     Need for modulation:
  • Avoids mixing of signals
  • Increase the range of communication
  • Wireless communication
  • Reduces the effect of noise
  • Reduces height of antenna
     Types of modulation:
      Modulation is classified into two types:
  • Analog modulation
  • Digital modulation          
     - Analog modulation:
  • In analog modulation, the analog signal is used as a carrier signal that modulates the analog message signal. 
  • In analog modulation, the characteristics (amplitude, frequency or phase) of the carrier signal is varied in accordance with the amplitude of the message signal.
     There are four basic types of analog modulation:
     - Amplitude modulation
     - Frequency modulation
     - Phase modulation
     - Pulse modulation
  • Amplitude modulation: Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the amplitude of the message signal while the frequency and phase of carrier signal remain constant.
  • Frequency modulation: Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the amplitude of the message signal while the amplitude and phase of carrier signal remain constant.
  • Phase modulation: Phase modulation is a type of modulation where the phase of the carrier signal is varied in accordance with the amplitude of the message signal while the amplitude of carrier signal remains constant.

    - Digital modulation: 
  • The digital modulation technique is employed for efficient communication. 
  • The main advantage of the digital modulation over analog modulation include high noise immunity, available bandwidth, and permissible power. 
  • In digital modulation, a message signal is converted from analog to digital message, and then modulated by using a carrier wave.
    
     There are three types of digital modulation:         
  • Amplitude shift keying:  Amplitude-shift keying is a form of amplitude modulation that represents digital data as variations in the amplitude of a carrier wave.
  •  Frequency shift keying: Frequency shift keying is a form of frequency modulation that represents digital data as variations in the frequency of a carrier wave.
  • Phase shift keying:  Phase shift keying is a form of phase modulation that represents digital data as variations in the phase of a carrier wave.  

     - Demodulation:
  • It is the process of recovering the signal intelligence from a modulated carrier wave. This process is also called detection, which is reverse process of modulation.