1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Communication systems -- Find the Modulation Depth...

  1. Jul 14, 2015 #1
    1. The problem statement, all variables and given/known data
    Hello, the plot in the image shows a modulated signal s(t), with one period of the modulating signal m(t). The mean value of m(t) is equal to zero . Its asked me to find the modulated index, the amplitude of the carrier, the equation of the message(m(t)) and the kind of modulation (DSB-SC or AM).

    2. Relevant equations
    s(t)=A*m(t)*cos*2*pi*fc*t) (dsb-sc modulation)
    s(t)= (1+ka*m(t))*cos*2*pi*fc*t) (am modulation)
    3. The attempt at a solution
    I don't know, I'm really stuck in this exercise.
     

    Attached Files:

    • com.png
      com.png
      File size:
      110.5 KB
      Views:
      65
  2. jcsd
  3. Jul 14, 2015 #2
    Have you tried plotting those questions with various values of the constants to help learn their meanings?
     
  4. Jul 14, 2015 #3
    Yes, I do. But I can't still figure out a solution for it.

    I tried to solve s(0)= (1+ka*m(0)), but I don't know who is m(t)
     
  5. Jul 17, 2015 #4

    NascentOxygen

    User Avatar

    Staff: Mentor

    The image seems to not show m(t). You are making this difficult for yourself if you ignore the assistance a sketch of the modulating signal will likely give you.

    If you are not shown m(t), perhaps you can figure it out, or even "guess" it?
     
  6. Jul 17, 2015 #5

    rude man

    User Avatar
    Homework Helper
    Gold Member

    I suggest:
    take the two s(t) signals in "relevant equations". Take one at a time.
    Can you imagine s(t)=A*m(t)*cos*2*pi*fc*t) (dsb-sc modulation) giving you the shown signal?
    Can you imagine s(t)= (1+ka*m(t))*cos*2*pi*fc*t) (am modulation) giving you the shown signal?
    Only one of those two can give you the shown signal.
    And a little thinking should get you the answers you seek.
    Hint: only one of your s(t) can produce a signal with differing maxima (5 and 15).
    P.S. obviously, m(t) is a sinusoid.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Communication systems -- Find the Modulation Depth...
Loading...