Drooping ends on multi band doublet

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K4IVH, Jul 24, 2021.

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  1. K4IVH

    K4IVH Ham Member QRZ Page

    Greetings! I have a DXEngineering multi band doublet for 80 - 10, which will be installed between two trees 125' apart. Even with the suggestion of a 110' shortened dipole, about the only way I can get 80 is to droop the ends 10' - 15' on each end. Any ideas on what effect this will have on 40 -10? Both in terms of loading and radiation patterns.
     
  2. RW4HFN

    RW4HFN Ham Member QRZ Page

  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    A Doublet is designed to be used with a tuner. It is cut to be roughly long enough for the lowest desired frequency/band. SWR is unimportant, and the antenna is not 'tuned" to be resonant on any particular band. It is a general purpose antenna, not optimized in any particular way.

    With typically high Impedance at many points, Transmission Losses are kept low by using a relatively high feed line like 450 Ohm Ladder/Window Line (about 1 Inch spacing), or traditional 600 Ohm Open Wire Line, (About 6 Inch spacing).

    Example:
    [​IMG]
     
    Last edited: Jul 24, 2021
  4. RW4HFN

    RW4HFN Ham Member QRZ Page

    NEC for MMana model.
    imgonline-com-ua-2to1-MhjiQdSWdvKWypLD.jpg
     

    Attached Files:

    Last edited: Jul 24, 2021
  5. K7MH

    K7MH XML Subscriber QRZ Page

    If that's what you have to do to put the doublet up, then that's what you do!
    Put it up as best you can, get on the radio and see how it is working for you and try to make improvements if you can. Sometimes it's just not possible.
    I have a 102ft doublet fed with window line up in a tree, inverted V style. The ends are about 6 ft off the ground. I added about 25ft on each leg and ran it along the top of my cedar fence so I could get on 160 easier. Just not so critical with the tuner anymore. It is easier to find the sweet spot on 160 and 80. Good enough for getting DXCC on 30, 40 and 80 so far.

    It's not the perfect doublet installation but it works for what I want it for.
    My thoughts are don't let antenna modeling (and also propagation reports) keep you from putting up an antenna or getting on the air. Just do it!
     
    W7KKX likes this.
  6. W7UDI

    W7UDI Ham Member QRZ Page

    Hi Warren,

    Try not to overthink this. Just put it up, you'll be fine. I just built a 80 meter OCF and hung it up between a couple of towers 100 feet apart. Hung down about 20 feet on each end and the antenna performed as expected.

    So go put it up, and go out and have fun on the bands.

    Good luck with your project.

    73
    Steve
    W7UDI
     
    K7MH likes this.
  7. 2E0CIT

    2E0CIT Ham Member QRZ Page

    I asked the same question a while back and got the same answer...let the ends dangle.

    My homebrew inverted vee doublet is 135 ft long squashed into in a 110 ft city back yard.
    It's 40 ft high at the centre and around 20 ft high at the ends.
    It's fed by 50 ft of 300 ohm window line to a 4:1 Guanella balun and remote atu at the base of the mast and then coax to the shack.
    (The feedline length is one of the 'magic' lengths for this configuration. It's fiddly to get the length correct but worth the effort.)

    It works great 80-6m ......which sometimes annoys me 'cos I love to build and experiment with antennas, trying to improve my station, but can't find anything to build that would work as well as this doublet does across the bands!:rolleyes:
    73 Jeff
     
  8. K1VW

    K1VW Premium Subscriber QRZ Page

    The majority of the radiation happens at the high current areas, which is generally near the feed point. I have drooping ends on my 40m dipole at one location, and I modeled it to satisfy my curiosity. As everyone said, it doesn’t make much difference.

    Before Drooping ends I had a big V sag in the middle because i couldn’t pull it taut. Getting the feedpoint higher is the objective, and pulling the dipole taut got the center up. The model said it would be an improvement, and it is.
     
    Last edited: Jul 25, 2021
  9. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    Perhaps not, but you can almost certainly find something that will work better for your favorite bands!
     
    2E0CIT likes this.
  10. RW4HFN

    RW4HFN Ham Member QRZ Page


    You guys are scaring me... For the second time in a week, I catch a post about the dangers of modeling... :D
     

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