Vertical hung delta loop

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WM4MM, May 27, 2021.

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  1. WM4MM

    WM4MM Ham Member QRZ Page

    Do to construction constraints I need to feed this vertical loop at the vertex (45 feet high) the base is 12 feet high.
    Why is this a bad idea. Really want to lower take off angle. You see this done with a vertex down arrangement but I havent seen it on a vertex up arrangement.

  2. KL2WX

    KL2WX Premium Subscriber QRZ Page

    Should be good to go, feet it at a bottom corner. That's how I'd do it if I were to put up a vertical delta loop anyway.
    VA3QY likes this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    What band?
    How wide can the base be?
  4. VK3YE

    VK3YE Ham Member QRZ Page

    The bottom corner is OK and convenient but you might get slightly better results if you feed it up from the bottom corner.

    Assuming the loop is an equal length on all sides (ie 1/3 wavelength) then you feed it 1/4 wavelength from the top apex (ie 1/12 wavelength from the bottom).

    Examples of me using one portable is here:

    AK5B likes this.
  5. K2XT

    K2XT Premium Subscriber QRZ Page

    If we are to take the OP at his word he is going to feed it at the top. He said so in his first sentence. Feeding it at a point where he could get vertical polarization (lower takeoff angle) is not a consideration.
  6. W9CYS

    W9CYS Platinum Subscriber Platinum Subscriber QRZ Page

    Feed it at the bottom corner for DX. Put up my 40m loop about 6 weeks ago and can FINALLY work into EU and western Asia consistently. Best 40m wire I ever put up! Apex at about 47' and base at 15'. Extremely happy with it.

  7. WM4MM

    WM4MM Ham Member QRZ Page

    Thanks BUT I physically need to feed it at the apex 45' up. 13 .3 meters equilateral sides.
    Other options IE: lower corner is blocked and cannot be used for feed line path.
    Fed with ladderline/balun. 40 -10 M coverage. QRP radio . Just trying to extend low takeoff for DX.

  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    Strange mixture of units.

    An isosceles triangle that is (45-12) = 33ft high, that has two 13.3m*3.28ft/m = 43.24ft sides, has a bottom that is 2*sqrt(43.24^2 - 33^2) = ~56ft long, for a total circumference of ~142ft.

    A 40m loop (that is also resonant on 20m, 15m and 10m) would need a circumference of about 1005/7.1 = ~141.5ft.

    Does that describe your loop?
    Last edited: May 27, 2021
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    Assuming that I guessed the dimensions in post #8, here is a picture:
    Pay attention to the wire lengths:
    Here are the resonances, feedpoint impedances, and where the max gain goes (you will not like it), over average dirt and with a base length of 54.66ft:

    This loop cries out for being fed with 50 Ohm coax and a 1:4 Guanella balun right at the top corner. Feeding it with some lengths of 600 Ohm OWL will totally screw up the impedances seen by the tuner. If it has to be twin-lead, then make it as close to 300 Ohms as possible.

    Here is a comparison between top feeding it, and moving the feedpoint down wire 1 so that it is about 25% of the way up from the wire 1-2 corner:
    Sorry, but that is why most folks choose to feed near the lower corner...
    Last edited: May 27, 2021
    K4PP, M0AGP, AK5B and 1 other person like this.
  10. WM4MM

    WM4MM Ham Member QRZ Page

    Thanks for all your work. I have lots to learn about the program you used.
    I kind of hoped it would be different. In the past I have put the balun in the air but now I put it outside the house and run coax from there to the radio. Using an mininano antenna analyzer I saw no reason not to do so.
    In order to clear my obstacle with the lead in I would have to suspend the lead in from the center at about the middle of the triangle.

    Thanks again.

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