Shortening a (40M) quarter wave vertical by bending the top over?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by VA3VX, Jun 18, 2020.

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  1. VA3VX

    VA3VX Ham Member QRZ Page

    Hello antenna ninjas,

    This is really a question about what happens if I bend the top 8' of a 33 foot 40 meter quarter-wave vertical over down to about 120 degrees. But if you want the background and my thinking, here it is...

    I'm about to semi permanently mount a tripod and a strong (DX Engineering) fiberglass mast on the apex of a 15' tall, all-wood storage shed (sides are 10' and there's a pyramid-shaped roof that adds another 5')

    I'm in an old urban neighborhood on a small lot with uptight neighbors, so there are a lot of constraints - one of them being a need for relative stealthiness :)

    I'm planning to use the single mast as the support for the apex of a 20 meter delta loop, which will put the top about 40' above the ground - and I'm thinking of center bottom feeding it for horizontal polarization.

    4 guying ropes will come down from the mast, each to a corner of the 'pyramid' rooftop on the shed. Two sides of the delta loop will follow two of the opposite guy ropes, just far enough down the guys that the horizontal element at the bottom will be just above the apex of the rooftop. Ya the mast will stick out like a sore thumb, but the guys and antenna wire are black, and if I do a tidy job, it shouldn't be too 'obnoxious'.

    Now I'm thinking, (always dangerous :) - I can also add a 40-meter quarter wave ground plane by running wire up the center of the mast, and running 4 wire radials sloping downward from the bottom of the mast out to the four corners of the pyramid-shaped rooftop. (They'll be a bit long but I can zig-zag them or let them hang down from the corners for a few feet).

    If it works, I'll have a decent loop for 20 that will resonate (somewhat) on 10m. And a decent vertical for 40 m that will resonate (somewhat) on 15 m. (I realize on 10 and 15 the antennae will likely be cloud warmers, but better than a dummy load :)

    Now to the point :) ...

    To get the apex of the delta loop up high enough that the angle of the guy ropes will be such that the two slanted sides of the loop can follow them, parallel, out to the opposite corners of the roof (and the horizontal third of the loop will still be just above the roof's apex). For this to work out, I estimate needing the mast to go up about 25'.

    Hrm... In order to run a full-size quarter-wave for 40 meters, I need the mast to reach about 33'.

    I do have enough mast to reach 33' - but back to the uptight neighbors... 33' is just that much more noticeable and 'scarier' to them than 25', so I'd rather not do that if possible.

    So off I went looking for ways to physically shorten a vertical - Ideally from about 33' feet down to about 25.

    Loading coil? Ya, but lossy and (frankly) just one more little thing to get wrong in a project that's already suffering from scope creep :)

    Capacity hat? Just that much more obvious, plus, see above :).

    Maybe linear loading with a little run of ladder line down the top few feet of the mast? Very little info online about how specifically to make that work. (Although as an idea it's tempting... :)

    So here's my lazy-assed but possibly workable question:

    What happens if I run the radiating vertical wire of the quarter wave up 25', to the top of the 25' mast, and simply FOLD the remaining 8' of antenna wire over and down along one of the guy ropes? (one that's at right angles to the ropes being used for the delta loop! :) ??

    I've looked for any type of info or antenna 'type' where this is defined, but I can't find it. It's not an inverted L, or folded, or linear loaded, or, or... :)

    If I do that, the radiating element is still the right length physically, only with about the top 8' folded down about 120 degrees from vertical. I'm sure it will add some inductive or capacitive impedance - although not sure how much or what it does to the effective length.

    With current at close to minimum at this end of a quarter-wave, I'm hoping it won't have a huge impact on take-off angle or directional radiation pattern... But I'm a total noob with EZNEC and will bungle modeling it with any confidence (or competence ;)

    Any thoughts, experience, calculations, models etc. are enthusiastically welcome :)

    Earl

    PS this is my delurking post here so please be gentle ;)
     
  2. AE1N

    AE1N Ham Member QRZ Page

    IF you have a good tuner you can load the antenna, however bent, on all bands ... it will radiate!
    ---Layne AE1N
     

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