. Addition of information to an electronic carrier signal.
 . Carrier Signal: Signal with constant amplitude and frequency.
 . Information can be added to carrier by varying its amplitude, frequency, phase.

Need of Modulation:

 . To transmit signals over larger distances.
 . To allow smaller antennas (for low frequency signals).
 . To reduce attenuation (low frequency signals).
 . Used in Radio, Lasers, Computer networks.
 . Can be applied to Alternating Current and Direct Current.

Types of Modulation:

Amplitude Modulation(AM):

  . First successfully carried out in 1870 to produce quality radio over telephone lines.
  . Amplitude of carrier signal is varied.
  . Frequency and Phase are kept constant.
  . Transmits information over larger distances.
  . It is simple to implement.
   . Used in News broadcasting.
  . Used in Aircrafts for communication between station and pilot and vice-versa.
  . Information is on the edges of signal (Amplitude).
  . Not suitable for Music broadcasting because it more prone to interference.

Frequency Modulation(FM):

  . Frequency of carrier signal is varied.
  . Amplitude and Phase are kept constant.
  . It is not simple to implement.
   Used in Music transmissions.
  Information is present within the signal.
  . Less prone to interference.
  . It is superior to AM in sound quality.
  . Most radio stations use FM instead of AM.


TransmissionAmplitude varies, Frequecy constantFrequency varies, Amplitude constant
Frequency range535-1705 KHz88-108MHz
Rate1200 bits/sec1200-2400 bits/sec
How it trasmits?By changing signal strengthBy changing frequency of signal
Sound qualityPoorGood
Used for:News programming, radioMusic channels
Radio Stations in world:16,26528,693