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Thread: Dipole feed line length

  1. #1

    Default Dipole feed line length

    Iíll make this quick, short, and to the point. I will provide more details if needed. Iím in the designing phase of building a dipole antenna. Iím using a ďair-choke/balunĒ from coax feed line at the dipole /feedline connection point.

    My question is pretty simple. In Basic dipole design theory, it is always said to make your feedline exactly 1/2 wavelength long. When calculating the 1/2 wave length of coax to put on this antenna, do I include the length of coax that is made to build the air-choke/balun in my calculation? Or do I just calculate the length of wire below the RF choke? Itís all part of the same line, just not sure at what point counts as the ďlengthĒ.

    I think what is confusing me is that you can buy commercially made dipole choke/baluns that the feedline ties into, though not ďtechnicallyď part of the feedline, itís all tied together. Do these count as feedline length since it still sits between the start of the antenna and the feedline itself?

    Lots of people also homebrew their own choke out of the feed line itself by coiling the feeding coax to an air choke. (Thatís what Iím doing). Does the coil count as total feedline length when calculating a 1/2 wave length feedline?

    all antenna builders online will tell you to calculate your feedline length 1/2 wavelength of maximum antenna performance.

    And yes, Iím considering velocity factor into my calculation for total length.

    I have an included random picture of a wound RF choke below. This is just a random picture, and not my own. Just showing it for reference. So please donít tear it apart as it is not my actual antenna picture.

    Sent from my iPhone using Tapatalk

  2. #2
    gnuuser's Avatar
    Join Date
    Apr 2020
    NW Pa,USA


    correction on dipole length not exactly 1/2 wave but more like 47 or 48% of a wavelength.will resonate better than a true 1/2 wave.
    I found this out quite by accident while making a 40 meter wire dipole.
    this also holds true on an inverted vee
    Im so old dirt was my apprentice

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