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Why is the optiamal element length 91% if half the wavelength for a dipole?

Discussion in 'Amateur Radio Antennas' started by RCA Dimensia, Sep 30, 2010.

  1. RCA Dimensia

    RCA Dimensia Member

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    "Actual best length of a dipole antenna is about 91% of that of 1/2 wave in free space, so to be precise about this, the lengths below are already reduced by approx. 9%."

    TV Rabbit Ear

    I meant OF the wavelength.


     

  2. KJ6HYC

    KJ6HYC Member

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    Assuming your statement is true. Perhaps the velosity of the wire?
     
  3. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    1005/freq gives you wl in free space

    468/freq gives half wl with velocity factor figured in sort of.

    234/freq gives 1/4wl with velocity factor figured in sort of.

    Will this formula hold up everywhere in every antenna build or installation?

    The answer is a big NO, but it will get you in the ball park.
     
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    That site in the original post is the only one I have seen that states 9% shortening. Everything else I have ever seen or heard states about 5% which is what I believe to be true unless you are using a really fat conductor on VHF/UHF frequencies. The reason is partly due to the velocity factor of the element material and mostley due to something called "antenna end effect" which is a small capacitance that is formed by the antenna elements in air and has the effect of "detuning" the antenna. In order to compensate the antenna length must be changed slightly.
     
  5. pizzaman

    pizzaman Member

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    You answered your own question, "in free space". As you bring your dipole into relationship with the ground the charistics of that antenna change.

    Bernie
    W8NBC
     
  6. Kamikaze

    Kamikaze Active Member

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    Optimal for what?
     
  7. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Proper tuning and operation.
     

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