Results 1 to 6 of 6

Thread: Folding The Antenna Wire Back On Itself??

  1. #1

    Default Folding The Antenna Wire Back On Itself??

    Good Morning All,

    I have a Dipole up at the moment which is too long by about 3 meters on each side.
    The desired centre frequency is to be 7.150.

    To shorten the antenna, can I just fold back each leg on itself by 3 meters to achieve a physical shorter antenna, or will it still be seen as a longer wire??


    Pete VK4CCV

  2. #2

    Join Date
    Oct 2009
    Location
    Oulu, Finland
    Posts
    614

    Default

    What happens if you fold the ends of a dipole?:

    https://www.qsl.net/kk4obi/Center-fe...orizontal.html

  3. #3

    Default

    Since the majority of the radiation comes from near the feed point, letting the ends hang down (perpendicular to the antenna) should not be too much of an issue. Make sure the antenna ends are out of reach of people as the voltage on the tips can be quite high depending on your power level. Try to place the bends symmetrically.

    Another option would be adding loading coils to each side of the dipole and trimming the wires shorter. The purpose of loading coils in series with each element is to cancel the capacitance caused by having the elements physically too short. Some people attach the loading coils directly to the feed point, but I prefer to have them further down the dipole to increase the current in the antenna before the coil.

    Regarding bending the ends back on themselves... My first thought is no.
    Although bending the ends back on themselves should be the same as adding an inductor to the end of a shortened wire, I don't think it will be easy. In theory, the net result would be a hairpin under 1/4 wavelength (which is inductive), but the inductance of a hairpin is a function of its length and its characteristic impedance as a transmission line. For a consistent effect, the hairpin wires must be held at a fixed distance apart and not move in the wind. I also doubt the math would come out to "simply fold it over". Although theoretically possible (i think), I believe the effort will be far greater than just adding some coils or letting the ends hang down perpendicular.

    EDIT: that's neat OH8GAD! If someone found a ratio where one does not need lots of math...
    Last edited by brandon lind; Fri 22nd Feb 2019 at 16:40.

  4. #4
    K7KBN's Avatar
    Join Date
    Jul 2008
    Location
    Bremerton WA USA
    Posts
    1,386

    Default

    I wouldn't worry about it on 40 meters. Folding back the ends of a too-long dipole hurts very little on HF if the "fold" is less than 1/4 wavelength in radius. Experiment! Learn by doing - that's what Marconi did!
    73
    Pat K7KBN
    Semper ubi sub ubi.

  5. #5

    Join Date
    Oct 2009
    Location
    Oulu, Finland
    Posts
    614

    Default

    I'm glad this post came up, because in my garden, the longest edge is just short of being long enough for a 20 metre dipole. I had one for 18 metres, but would like to go to 20.
    It seems that if you're dropping the ends for practical reasons, such as available length, the main factor is height above the ground - try to keep it more that 10th the wavelength, which for 20 metres is two metres, so that shouldn't be too much of a problem.

  6. #6

    Default

    If the antenna wire is bare, when you fold it back on itself it becomes a thicker conductor for the portion of overlap. I do it all the time to tune my antenna to a higher frequency. In fact, you can fold back a small amount and scale the amount you need to get your desired frequency.

    Hope this helped you, Dave Reed ac0yw

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •