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How is wireless data sent over the airwaves?

  1. May 11, 2015 #1
    So you start with electromagnetic radiation(Maxwell) and magically send 'data' over the atmosphere to a receiving device.

    EM radiation consists of photons, not electrons(I think), and the only way to detect a photon is through the photo-electric effect. I also have heard of frequency modulation.

    So how can photons be streamed to a mobile device.
     
  2. jcsd
  3. May 11, 2015 #2
    In the end, wireless data is nothing but digital radio. I suggest perusing the Wikipedia article:

    https://en.m.wikipedia.org/wiki/Radio

    That should probably clear up a lot of initial questions. Feel free to ask follow-ups.
     
  4. May 11, 2015 #3

    CWatters

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    Science Advisor
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    The effective "size" (de Broglie length) of a photon depends on the frequency. The higher the frequency the "smaller" the photon. For low frequencies (eg radio rather than light) the effective size of the photon is quite big (meters). At these frequencies it's better to think of them as waves rather than particles/photons.

    There are many ways to encode or modulate data onto a radio wave. The two most commonly used for Radio stations are still variations of..

    AM
    http://en.wikipedia.org/wiki/Amplitude_modulation
    FM
    http://en.wikipedia.org/wiki/Frequency_modulation

    Lots of other listed here..
    http://en.wikipedia.org/wiki/Modulation
     
  5. May 11, 2015 #4

    Drakkith

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    At radio frequencies, photons are indistinguishable from classical EM waves and can be detected by the effect the EM wave has on the charges in antennas. The EM wave moves them back and forth in time with the frequency of the wave, and various techniques have been developed to transmit information using these waves. Frequency modulation and amplitude modulation are two of them.
     
  6. May 11, 2015 #5
    No, this is not the only way. The receptors in the retina can detect photons, for example. And there is no photoelectric effect involved. Molecules may be excited by photons without emitting photoelectrons.
     
  7. May 11, 2015 #6

    Svein

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    Well, Wi-Fi (IEEE 802.11, see http://en.wikipedia.org/wiki/IEEE_802.11) uses spread-spectrum and other advanced techniques in order to minimize interference from other devices (see http://en.wikipedia.org/wiki/Spread_spectrum).
     
  8. May 11, 2015 #7

    Drakkith

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    Staff: Mentor

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