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Harmonic carriers

Discussion in 'Electronic Design' started by Martin Harris, Jun 23, 2007.

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  1. I am trying to understand how an harmonic carrier is properly applied
    and what the effect is.

    For example, if I tale a 1KHz sinewave and use it to AM a 16KHz
    sinewave do I get harmonics higher than the 16KHz?

    Any expert insight?

    Martin Harris
     
  2. Hal Murray

    Hal Murray Guest

    I'm far from an expert, but that's pretty basic.

    You will get energy at 16-1 and 16+1 KHz. No harmonics of the carrier.

    You will get harmonics/splatter if you overmodulate.


    http://en.wikipedia.org/wiki/Amplitude_modulation
     
  3. Ideally, no. But, no system is perfectly linear. There will be some
    level of harmonic response. How much is acceptable and why are the
    questions.
     
  4. Rich Grise

    Rich Grise Guest

    Not harmonics - sidebands. If your 16KHz is a pure sine wave, and your
    1 KHz is a pure sine wave, and your modulator is "linear" (modulation
    is a non-linear function - what I mean here is that the amplitude of the
    carrier exactly follows the input), then the output will consist of
    a signal at 15KHz, 16KHz, and 17KHz - the two sidebands will be half
    the amplitude of the carrier (16KHz)

    http://www.google.com/search?hl=en&q="amplitude+modulation"+tutorial

    Hope This Helps!
    Rich
     
  5. Chuck

    Chuck Guest

    As has been said by the other posters,
    if you start with ideal sine waves and
    modulate linearly, the entire output
    spectrum will consist of just three pure
    sine waves.

    Perfect amplitude modulation wouldn't
    generate harmonics of the carrier.
    However, AM is often applied to a
    high-level stage or power amplifer that
    is operating in some mode other than
    class A with less then perfect high-pass
    filtering. Consequently, that stage will
    generate harmonics of the carrier
    frequency. And if the carrier is being
    modulated, so will the harmonics. But it
    is not the modulation process that
    generates the harmonics of the carrier.

    Does that answer your question? If not,
    maybe you can supply some additional
    details.

    Chuck
     
  6. Due to the nature of my inquiry, it was assumed I wanted to minimize
    harmonics. Understandable by convention. But actually, I would like to
    _maximize_ them, especially on the higher side. IOW to obtain as many
    higher above audio harmonics of the 16KHz as possible while still
    using something like the sinewave AM approach originally described,
    ie. not squarewaves. What would be the best way of achieiving this?

    Martin Harris
     
  7. Phil Allison

    Phil Allison Guest

    "Martin Harris"

    ** Physics is not game where YOU get to make up any rules you like -
    fuckwit.

    Harmonics are generated by distorted looking wave shapes - NOT sine waves.

    A square wave has all the odd numbered harmonics included - 3rd, 5th 7 th
    etc. .

    Asymmetrically distorted sine waves have the even ones, 2nd 4th, 6th etc.

    A mix of the two gives you the lot.

    An electric guitar fuzz box does this to a sine wave input.



    ....... Phil
     
  8. Robert Baer

    Robert Baer Guest

    Not quite correct; one gets the sum (16+1), the difference (16-1),and
    the originals (1 and 16) KHz.
     
  9. Robert Baer

    Robert Baer Guest

    Why is it that "everyone" is ignoring *both* of the original input
    frequencies?
    Perhaps one needs to use a spectrum analyzer...
     
  10. Robert Baer

    Robert Baer Guest

    Use a filter tuned to 17KHz.
     
  11. Chuck

    Chuck Guest

    Kind of depends on the circuit, doesn't
    it, Robert? What if a DBM were used?

    If the intent is to produce modulated
    harmonics of a sine wave carrier, I
    think the answer has been given: you
    must modify (i.e., distort) the sine
    wave carrier in order to produce
    harmonics. For example, use a circuit
    that distorts the sine wave by clipping
    it. The modulator could perform this
    function.

    A pure sine wave simply contains no
    energy other than at its own frequency.
    If you're not willing to distort a sine
    wave, you can't produce harmonics. Period.

    Without knowing more about the
    parameters of your enterprise, it is
    really difficult to respond further.

    Chuck
     
  12. Rich Grise

    Rich Grise Guest

    Just generate a 16 KHz sawtooth; you'll get harmonics:
    http://en.wikipedia.org/wiki/Sawtooth_wave

    Or, if you want there to be harmonics of 1 KHz all around the 16 KHz
    carrier, them AM it with a 1 KHz sawtooth.

    Have Fun!
    Rich
     
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