WHY POSITIVE MODULATION AND NEGATIVE IN AM modulation

Discussion in 'General Electronics Chat' started by saif ur rehman, Mar 18, 2016.

  1. saif ur rehman

    Thread Starter New Member

    Mar 18, 2016
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    WHAT IS THE MEANING OF NEGATIVE MODULATION IN AM MO0DULATIO
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  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If your talking about a TV signal, the lower the carrier amplitude the lighter the picture, the bigger the carrier amplitude the darker the picture, this is to reduce noise spots,.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    All voltages are relative. With AM modulation, it is most convenient to reference the signal voltage against the center, mean level, and to call that 0V. That requires half of the signal to be at a negative voltage.

    Is that what you were asking?
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    positive and negative modulation are terms usually used in cb radio language, meaning that a watt meter goes up or down with modulation. 100 % modulation has the same amount in both dirrections.
     
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  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    And be aware, you can never exceed 100% negative modulation, while it's possible to have much more than 100% modulation, if using an asymmetrical audio signal. A.M. broadcasting allows 130% positive modulation peaks (in the U.S.)
     
  6. saif ur rehman

    Thread Starter New Member

    Mar 18, 2016
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    I mean when we say that there are three frequencies that is f+f1 and f-f1 which is ploted in negative axis
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  7. Dodgydave

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    Jun 22, 2012
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    Neither you're talking about SSB modulation, Upper and Lower carriers are just separated by about 10khz bandgap.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    When you superimpose two sine waves, the carrier and the modulation, they beat, or form interference patterns, and you will find power appearing at the frequency of the carrier plus the modulation frequency, and at the carrier minus the modulation.

    If your prefer math, go see this. A more visual description here.
     
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