40/80 vee and ground loss

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AC9KW, Sep 8, 2017.

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  1. AC9KW

    AC9KW Ham Member QRZ Page

    I am currently building out an inverted vee for 40/80. the height is about 38-40ft. I have a smaller lot so I am unable to have the elements full size, I am limited to at most 50ft. per leg. Currently I have a ~140ft. vee with about 25ft of each leg running parallel to the ground about 5ft in height, in a "Z" shape, fed with windowed 450 ohm line and the smaller johnson matchbox. While the antenna works, I am not happy with the current distribution on 40m.

    The plan is to put up a loaded vee. I have coils made up, about 60-70uH. I have built and varnished them so that variable is pretty much set. Modeling this antenna, the current nodes on 40 are higher along the elements than the 140 unloaded vee, which is what I was shooting for. My concern is ground losses.

    I have a couple of questions before I start cutting wire. Parameters:

    I have ~110ft of ladder line, I would like to leave the feedline length the same.
    The loading coils are constructed, 60-70uH. I do not want to rewind them.
    ~50ft per leg max element length.

    Running models, the numbers are close. if I cut for ~390 ohm feedline, the element ends are ~4ft above ground and the loading coils are about 10ft above ground. If I cut it a bit shorter, I think I can still match with the matchbox, and the ends would be 8ft above ground with the coils 13 ft high.

    My concern is ground loss. I want to make this antenna as efficient as possible. Am I splitting hairs at this point? Is the 4ft addition in height going to matter much as far as ground losses?
     
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Before trying to figure this, I'd want to know what creates the 38-40' center height restriction?
     
  3. AC9KW

    AC9KW Ham Member QRZ Page

    Tree used as support, best height I can get and still thread elements through branches.
     
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Would it be possible to not use the tree, but install a tall mast on the house to get some free extra height?
     
  5. AC9KW

    AC9KW Ham Member QRZ Page

    Unfortunately not :(
     
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Why not?

    If you have a house, the first 12-30' or so (depending on the house) is free height. Easy to add to that.
     
  7. AC9KW

    AC9KW Ham Member QRZ Page

    I live in a single story house, apex at 15ft. I have a roof tower supporting a hexbeam, baseplate at 30ft. No structures in the side yard, and the maple takes up most of the back.
     
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    With the roof tower and Hexbeam...you can extend the mast above the Hexbeam (although many designs bring the coax out the top of the mast, which was a silly design...but anyway...) clamp a longer mast to the Hexbeam mast and you might get your inverted vee up 50 feet where it will work better and the ends will be higher above ground. I'll assume the beam is on a rotator, so you'd need a floating ring for the inverted vee to keep it in place and prevent trying to rotate it. Those cost $3.

    To me, that's the obvious solution.
     
  9. AC9KW

    AC9KW Ham Member QRZ Page


    That would be one way to go, but I was more interested in detail about ground loss and the height of element ends above ground. I have run a couple of models and the eff. improves by only 2% at most, but I am not sure if the model is accurate. I have seen several people post recommended heights anywhere from a couple of feet to 15ft.
     
  10. AI3V

    AI3V Ham Member QRZ Page

    You are splitting hairs on the hairdoos of Angeles going out dancing on a pin.

    With the time and effort you are spending you could have went out and drive for Uber and made enough money to get a tower.....

    Rege
     

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