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Thread: 2.7m antenna?!

  1. #1
    Spectacular Butter Newbie
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    Default 2.7m antenna?!

    Hi i tried calculating the best antenna length suitable for a 27mhz tranmission

    (speed of light / freq) / 4 = 2.7 metres!!

    Is there any work around to this problem? By the way, is it alright if i use normal insulated wires for antenna?


  2. #2
    TheOne Newbie
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    For CB transceivers using this frequency, the length is often shortened by a method of loading at the top or bottom.


    http://www.tpub.com/content/neets/14.../14182_218.htm

    http://eweb.chemeng.ed.ac.uk/jack/ra...e/loading.html

    http://www.w8ji.com/mobile_and_loaded_antenna.htm

    In a similar way MW radio antenna towers are often equipped with a "capacitive hat" to make the antenna "think" it is longer than the actual length.

    http://www.antennex.com/shack/Oct04/cp-th.html
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  3. #3
    Super Moderator Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent Nigel Goodwin Excellent
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    Quote Originally Posted by TheOne
    For CB transceivers using this frequency, the length is often shortened by a method of loading at the top or bottom.
    Yes, it's common - but it severely reduces the effectiveness of the aerial, and makes it far more prone to interfering with other services (as it's more effective at harmonic frequencies).

    CB in the UK restricts use to such aerial though!.
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  4. #4
    TheOne Newbie
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    It is to be expected, the loss of effectiveness, cause it is physically smaller. (Nothing is free )The loading only ensure that there's a impedance match with the reduced length, but with the penalty of reduced radiation

    As a wise man once said "Any problem has a solution, any solution will create a new problem"

  5. #5
    Gaston Okay
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    the length of a half wave dipole would be = 468/mhz. results will be in feet
    for a quarter wave antena dived this in half

  6. #6
    Juglenaut Newbie
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    Don't forget about speed factor through conductors.

    I forgot this factor but will look into it.

    I would use standard brass telescoping nickle plated antannas.
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