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How to calculate R and C for Am Demodulation envelope detection?

Discussion in 'General Electronics Discussion' started by Bilal12, Oct 22, 2015.

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  1. Bilal12

    Bilal12

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    Oct 22, 2015
    Hello , one question if posible .

    How can I calculate the value of R and C for an Am Demodulation envelope detection circuit.

    Knowing that the carrier wave is 20KHz, 1Vpp, and the message signal is a 32Hz, 2Vpp, with a 5V DC offset:

    [​IMG]

    and thank you.
     
  2. Martaine2005

    Martaine2005

    2,575
    695
    May 12, 2015
    Hi Bilal12,
    Firstly, I would cheat! As the equations turn my brain to mush!

    I would stick a 1K and a 1nf to start. Or a varistor. And adjust the cap. Maybe 5nf 10nf.
    But have a read of the books as the equations are all there.

    Martin
     
  3. Martaine2005

    Martaine2005

    2,575
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    May 12, 2015
    It would appear your question has already been answered on another forum!
    The equations were there too.
    39nf and 5.1K

    Martin
     
  4. Bilal12

    Bilal12

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    Oct 22, 2015
    thank you for your replay . but who did you get c=39nf and r=5.1K
     
  5. Martaine2005

    Martaine2005

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    May 12, 2015
    Have you forgotten all the web sites you asked?

    Martin
     
  6. duke37

    duke37

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    Jan 9, 2011
    Your circuit looks very strange, shouldn't the ground terminal of the scope be connected to ground.
    I would not know how to calculate the values but R needs to discharge C fast enough to follow the wave form. The DC offset will affect the discharge rate and may allow 100% modulation to be detected without distortion.
     
  7. Bilal12

    Bilal12

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    0
    Oct 22, 2015
  8. Arouse1973

    Arouse1973 Adam

    5,164
    1,080
    Dec 18, 2013
    I think if you started off with an RC of 5 times the 1/fm (modulation frequency) and see how you go. There is a lot of contention over what formula to use. So try this first and see how you get on.
    Adam
     
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