what is modulation

 

                               Modulation


Modulation is the process of encoding information from a message source in a way that is suitable for transmission. This is achieved by altering the characteristics of a wave. By superimposing a message on to a high frequency signal known as a carrier wave (or sinusoidal signal), video, voice and other data can be transmitted.



                                         TYPE OF MODULATION


Analog modulation ;    In analog modulation, a continuously varying sine wave is used as a carrier wave that modulates the message signal or data signal.






 

Amplitude modulation

Amplitude modulation or AM is the method of varying the instantaneous amplitude of carrier signal accordingly with instantaneous amplitude of message signal.


 

Frequency:

The frequency of a wave is the number of waves passing a point in a certain time.

 

Frequency modulation

FM or Frequency modulation is the process of varying the in instantaneous frequency of Carrier signal accordingly with instantaneous amplitude of message signal.




Phase:

Phase is the position of a point in time (an instant) on a waveform cycle.


Phase modulation

PM or Phase modulation is the process of varying the instantaneous phase of Carrier signal accordingly with instantaneous amplitude of message signal.




Digital Modulation

Digital modulation is similar analog except base band signal is of discrete amplitude level. For binary signal it has only two levels, either high or logic 1 or low or logic 0.

The modulation scheme can be broken down in to three main types.

  1. ASK or Amplitude Shift Key
  2. FSK or Frequency Shift Key
  3. PSK or Phase Shift Key


ASK ( Amplitude Shift Key)

This form of modulation is when the carrier amplitude is varied in proportion to message signal.





FSK ( Frequency Shift Key )

This type of modulation transmits data by varying the frequency of the carrier. In this modulation, the carrier has two predefined frequencies.




PSK ( Phase Shift Ke )

With PSK, the phase of the carrier is shifted to transmit data.







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