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Radio wave speed

  1. Aug 8, 2007 #1
    first HI to everyone!

    I have a question:

    is there a (simple) way to reduce radio wave speed at it's source - transmitor (e.g. to 100 or 1000x less then the speed of light)?

    thx in advance
     
  2. jcsd
  3. Aug 8, 2007 #2

    ZapperZ

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    Unless you are transmitting it in an ordinary dispersive medium, or a waveguide, no.

    Zz.
     
  4. Aug 8, 2007 #3

    sorry but I have only basic phsycs knowledge. So ... what is an ordinary dispersive medium?

    thx
     
  5. Aug 8, 2007 #4

    ZapperZ

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    Example: water, glass, etc.

    Zz.
     
  6. Aug 8, 2007 #5

    Mentz114

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  7. Aug 8, 2007 #6

    ZapperZ

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    But again, those require a medium. The NEC experiment from a few years ago requires an "anomalous" dispersive medium. Things will still go back to normal if the signal goes back into air/vacuum.

    So unless one is willing to live in water or in those medium, there's nothing one can do to change the speed of light.

    Zz.
     
  8. Aug 8, 2007 #7

    Danger

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    Hi, Mixy.
    I don't suppose that simply introducing a delay circuit into the transmitter would simulate the effect enough for your purposes? What I mean is, do you actually want the signal to go slower, or just get there later?
     
  9. Aug 9, 2007 #8
    Thx for the help.

    Danger: no, just interested in actually slowing it down (travelling thru air)
     
  10. Aug 9, 2007 #9

    chroot

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    You can design a signalling standard based on phase velocity instead of group velocity. Then you can accomplish arbitrarily slow transmission of information, even though the actual signals propagate at c.

    - Warren
     
  11. Aug 14, 2007 #10
    Is there an estimation on how much velocity is reduced (average) in using radio waves in cities or populated regions (trees, hills, houses, etc.) ?

    Is this frequency dependent?

    thx
    Miha
     
  12. Aug 14, 2007 #11

    russ_watters

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    Sending radio through a city is still just sending it through air. A building can block or reflect radio, but won't slow it down.
     
  13. Aug 14, 2007 #12
    so, a radio wave would travel the distance from point A to point B in constant time T, no matter what stands between this two points (buildings, trees ...) ?
     
  14. Aug 14, 2007 #13

    Integral

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    Pretty much, yes. You can get reflections which can mean that the same signal can take different paths to reach the same point, but the speed is the same.
     
  15. Aug 14, 2007 #14
    but wouldn't it take longer then - if the signal takes different paths (consider measuring time T in nano or piko seconds)?
     
  16. Aug 14, 2007 #15
    Takes longer because the path length is longer, the speed stays the same.
     
  17. Aug 14, 2007 #16

    jtbell

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    In analog television received over the air with an antenna, this is what causes "ghosts:" faint secondary images that are shifted slightly to one side of the main image on the TV screen. Reflected signals from a large nearby object (building, water tower, etc.) take slightly longer to reach the antenna because they have to travel a longer path.
     
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