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Discussion in 'Electronic Basics' started by AssTelescope, Dec 26, 2004.

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  1. AssTelescope

    AssTelescope Guest

  2. I think that this size dish is too small for the 2.4 GHz that the can
    antenna is putting out. Probably a lot of the signal just goes out the
    back and is wasted.
     
  3. Clarence_A

    Clarence_A Guest

    ???
    At 2.4GHz a full wave is .00041 inches. The reflector will work just fine!
    getting it at the focus is more of a problem.
     
  4. You'd better recalculate that wavelength. More like it's a bit less
    than 5 inches. And that antenna dish was made for frequencies much
    higher than 2.45 GHz with wavelengths much shorter.
     
  5. In my universe, the wavelength in free space is more
    like 4.9 inches at 2.4 GHz. I'm willing to believe c
    is different in your neighborhood, but please tell me
    how you post here from over there.
     
  6. Clarence_A

    Clarence_A Guest

    SB 4.1 inches....... !
    Yes, bad copy.... The point was that the reflector is made for 8 to 10GHz, so
    it will work. IF the feed is at the focalpoint.
     
  7. Clarence_A

    Clarence_A Guest

    Gee, I guess I shouldn't try to convert from meters to inches in my head...
    12.5 mm IS closer to 4.9 inches.
     
  8. John G

    John G Guest

    12.5 mm is 0.4921259 inches on this planet and has been since the French
    invented the metre.

    But then the metre is an unknown standard in the USA isn't it?
     
  9. Terry

    Terry Guest

    Nope: Ignoring the banter. It's 4.9 inches!

    At 2.4 gHz One Wavelength = 300/2400 = 0.125 metres = 12.5 centimetres

    Centimetres!
    (A typical 6" 8" doorway is roughly two metres or two hundred centimetres
    high).
    And one hundred centimetres is roughly 39.3 inches.
    So 12.5/100 x 39.3 = 4.9 inches.

    But the 'probe' that launches and receives the signal would presumably be
    one quarter wavelength? To match the 50 ohm feed line?
    So probe length (inside the can and hopefully at the dish focal point?)
    would be 4.9/4 = 1.23 inches approx?????????

    The dish being 'too small', having been designed for 10 gigahertz would have
    only a portion of the capture area . It would therefore exhibit a 'loss' or
    'lower gain' at 2.4 gHz? Possibly expressed in decibels?

    f w
    m.hertz centimetres
    300 100 (One metre)
    600 50
    1200 25
    2400 12.5
    4800 6.25
    9600 ` 3.125

    Here in Canada we are becoming pretty well bilingual in regard to metric or
    non-metric.
    We measure building materials both ways. Gasoline in litres and distances in
    kilometres. Car engines in may countries have been measured in litres/ccs
    for years! Radio wavelength which is inversely related to frequency has been
    measured in metres almost from the word go.
    I've never heard of radio station frequency or wavelength measured in feet
    or miles?

    Terry.
     
  10. Clarence_A

    Clarence_A Guest

    One quarter the size would reduce the gain by about 6db. Still substantial!
    Can't spell it, but it MUST be the way to go?
    BTW, you buy 'petrol' in liters, distance is approximated in Kilometers, and
    all are convertible to usable numbers with care if the person doing it isn't
    too tired!

    Seems pretty easy to tweak you guys. :)>)
    However 'metric meters' are a rather recent invention. Feet and inches were
    used since the invention of radio. Before that "Cubits" "fathoms" and
    'leagues' were the standard!
     
  11. No it isn't...12.5 cm is 4.9-whatever inches.

    Tom
     
  12. Clarence_A

    Clarence_A Guest


    Perhaps you mean 4.9212598?
     
  13. John G

    John G Guest

    Wrong again.

    Whatever you think, 12.5 mm is really 0.4921259 inches.

    Yes the wavelength at 2.4 gigahertz is 4.92 inches or 12.5 CENTIMETRES
    but I was replying to the conversion in the previous post which was
    MILLImetres to inches
     
  14. I think you had better try again - practice makes perfect. 4.9 inches
    is right, but 12.5 mm is about a half inch. Try 12.5 CM.
     
  15. No, it is not. Rulers and tape measures come with both scales.
    So the ultimate question is, "Wot's Your Real Problem?"
     
  16. Well, the way I figured it is 3x10^8 / 2.45x10^9 = .12245 meters =
    12.245 CM

    ..12245 * 39.37 = 4.82 inches.

    Of course, that xdoesn't take into account that the speed of light is a
    bit less in the antenna, so it's maybe 5% too long.
     
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