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Pre emphasis net work

  1. Dec 1, 2011 #1
    I will be thankful if any one clears the following doubts in the concept of pre-emphasis in a FM transmitter in a simple way.

    1. In the higher secondary physics text book published by Tamil Nadu government, regarding the pre-emphasis net work, it is given as follows:"Since the modulating AF signal is having uneven power, it is fed into the pre emphasis network where all the frequencies of the modulating signal are given equal power". But, in all the articles I browsed through the net, it is given as follows: " the pre emphasis net work increases the amplitude of the higher frequencies of the signal before modulating them, as the higher frequencies are noisy".Is there any contradiction between the two statements?

    2. What is the exact meaning of the pre-emphasis and why it is needed?

    3. Compared to AM, it is said that the FM is noise free, as the noise is a form of amplitude variations, and since in FM only frequency of the carrier wave is modulated it will not carry noise with it. But then, how come that high frequency signal cause noise in the process?

    I will be happy if any body clarifies above points in a simple language.
  2. jcsd
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