ANALOG AND DIGITAL COMMUNICATION SYSTEMS

 PRE-EMPHASIS : Artificially increasing the strength of amplitude & frequency components of a message signal before modulation process is called pre-emphasis . or Strengthening the message signal before modulation process is called pre-emphasis  DE-EMPHASIS : Artificially reducing the strength of amplitude & frequency components of a message signal  after de-modulation process  is called de-emphasis . or reducing  the strength message signal after de-modulation process is called de-emphasis

 ADVANTAGES OF PRE-EMPHASIS AND DE-EMPHASIS Signal to noise ratio is high noise is eliminated provides original quality signal maintain high fidelity reduction of unwanted signals

 NOISE :- It is an unwanted form of energy which user not required  it interfere with the message signal and changes the message signal properties. Effects of noise in communication systems :- It increases the transmitting power noise will be present in the receiver radio/loud speaker it may cause increase / decrease the signal bandwidth Noise effects the sensitivity of the receiver because of noise the message may not be proper for receiver to understand

 CLASSIFICATION OF NOISE : NOISE : It is an unwanted energy signal ,which added at channel noise can be divided in to two types (a)  External noise  (b) Internal noise (a) External noise :  i) atmospheric noise ii) extra terrestrial noise iii) man made noise (b) Internal noise  :  i) thermal noise ii) shot noise iii) transit time iv) miscellaneous noise  EFFECTS OF NOISE IN COMMUNICATION SYSTEM : noise will degrade the system  performance . the receiver can not understand original message signal . reduce the efficiency of communication system

  NOISE : -   Noise is an unwanted energy signal ,with combines with the original message signal and change the properties of message signal . Noise is added majorly in the '' modulation section ''of transmitter  . S/N RATIO :-   It is ration of signal power to the noise power . S/N RATIO = signal power / noise power if S/N ration is high noise is less.  FM had more s/n ration then AM. NOISE FIGURE :-  It is defined as the ration of signal to noise ration in-put to signal to noise ratio output N.F = (S/N) INPUT  /  (S/N) OUTPUT NOISE TEMPERATURE :- It is the noise added due to heat , the heat maybe produced    due to electronic components or climatic conditions