fm/am Modulation in space

Discussion in 'Wireless & RF Design' started by sleeping, Oct 19, 2012.

  1. sleeping

    Thread Starter New Member

    Oct 19, 2012
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    Maybe a dumb question. Is freq/amplitude/pm/etc. possible in free space without the signals being on a say pc board. In other words if two signals crossed in free space would you get a third signal that is modulated by the two frequencies. I swear its not homework. This question has bothered me for years, just couldn't think of a good way of testing it out.

    Thanks, for any answer that makes fun of or helps me understand :)
     
    Last edited: Oct 19, 2012
  2. WBahn

    Moderator

    Mar 31, 2012
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    In general, no. In true free space (vacuum), the answer may even be categorically no (I'm not willing to go out on a limb like that off the top of my head). In order to get modulation, you need some kind of a nonlinear medium or process. For EM signals intersecting in a material (gas or glass or something else), if the intensities are high enough it could drive the medium into nonlinear behavior and you would get modulation. There are devices, particularly in the laser world, that rely on this mode of operation.
     
  3. sleeping

    Thread Starter New Member

    Oct 19, 2012
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    From your answer, I suppose you need extremely high energies of EM waves for them to react in a vacumn. Searching this further, Gamma rays show this behavior.

    Thank you for the reply.
     
  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Although radio waves can never mix in a vacuum regardless of how much power one has (this is the Superposition principle), the CAN mix in the ionosphere. This is the whole basis of ionospheric modification facilities such as HAARP, and the now defunct Hipas Observatory, where I worked for years. The non-linearity of the ionosphere was first recognized as the "Luxembourg Effect" and is a fascinating branch of plasma physics.

    Eric
     
  5. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    At the frequencies we normally think as radio vacuum is linear but at the much higher wavelengths and energies seen at the gamma ray scale vacuum becomes non-linear and EM "mixing' happens in bulk space.

    http://en.wikipedia.org/wiki/Schwinger_limit
     
  6. WBahn

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    Mar 31, 2012
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    Good article - shed a lot of light on my understanding of pair-production.
     
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