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Wireless Frequencies

  1. Aug 1, 2004 #1
    Okay, this may sound like a dumb question, but if i were to create a wireless signal with a frequency of red light for example, how come i would not see red light... or would i? Is this a difference caused by real and virtual photons?
     
  2. jcsd
  3. Aug 2, 2004 #2
    Creating red light IS creating a wireless signal with a frequency that of red light.
     
  4. Aug 2, 2004 #3
    I guess what i mean to say is that if i had an antenna and i kicked the frequency up to 430 THz (somehow) would i see red light?
     
  5. Aug 2, 2004 #4

    Nereid

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    Yes.

    What type of antenna do you think you'd need?
     
  6. Aug 2, 2004 #5

    turin

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    If you loosen your definition of "antenna" ...
     
  7. Aug 2, 2004 #6

    russ_watters

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    Right - a light bulb is, in a loose sense, an antenna transmitting at a wide frequency range.

    edit: light bulb isn't a great analogy - laser is better. And lasers are even used for wired and wireless communications.
     
    Last edited: Aug 2, 2004
  8. Aug 2, 2004 #7
    err, so what i meant by antenna is like a standard antenna! The type a cell phone or 802.11g card has.
     
  9. Aug 3, 2004 #8

    russ_watters

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    In that case, no. An antenna like that has a fairly narrow range of frequencies it can transmit/receive in due to the physical size of the antenna and construction of the transmitter.
     
  10. Aug 3, 2004 #9

    Nereid

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    If you would like to consider the infrared rather than optical, and consider highly directional paths rather than sectors (though even mobile/wireless technology is moving strongly to beams, to increase frequency re-use), then free-space optics may be what you're interested in. The idea? Think optical fibre, without the fibre. :smile:

    The 'antennae' look rather different than what's on a mobile handset. :eek:
     
  11. Aug 3, 2004 #10
    Okay, can it not transmit / receive because of capacitances in the antenna making it act as a filter?
     
  12. Aug 3, 2004 #11

    turin

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    Think about how large a half-wave dipole would need to be for even red light (L = 400 nm at the longest). Then, how would you couple to your antenna? The thinnest wires I've ever seen would have a diameter on the order of the length of your antenna, and at those frequencies, you can't afford the random surface current effects that this would cause. And related to this issue, the dipole would need to be so thin that QM effects would dominate any of the CM effects that you would be trying to achieve. You're best bet is to use a diode. This is even done often all the way down to the microwave frequencies (Gunn diodes in horn antennas).
     
  13. Aug 3, 2004 #12
    I think i get what you're getting at.

    My EM knowledge is, to put it bluntly, very weak. Sadly, i have to wait a while, due to the course offering schedules and my own, to take the two other courses in it that i plan on taking.
     
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