Analog Modulation

PART I : AMPLITUDE MODULATION

     WHAT IS ANALOG MODULATION?

•        Analog modulation consists of two parts :

1.         Analog message
2.         Carrier 

•       Analog message is then impressed upon the amplitude, frequency or phase of the carrier.
•       We then say carrier is “modulated” by the message.

Amplitude Modulation :

•        Define the message by a baseband signal m(t).
•        Define the “carrier” by a sinusoidal signal c(t) with amplitude Ac and frequency fc.
•        The AM signal is then given by 

  

    

      AM Envelope :

•         The “envelope” of an AM signal is the factor in front of the carrier,

                         

•        Envelope is a baseband signal and contains all the information an AM signal carries.
• 
  

    Requirements on the Envelope :

•        To prevent “overmodulation”, the envelope must always be positive,

                                                                                  

Overmodulation

Finding AM Spectrum :

•       Fourier transform modulation property says

•       Taking Fourier transform

•