Parallel Dipoles in the Attic

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WD9DWT, Jun 1, 2021.

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  1. K9UR

    K9UR Subscriber QRZ Page

    You would use a 1:1 balun -- a dipole is inherently between 50 and 72 ohms depending on the leg orientation.
     
    WD9DWT likes this.
  2. WD9DWT

    WD9DWT Ham Member QRZ Page

    Yep. I learned quickly that you can toss the free-space impedance vs. height curve in the trash for antennas in the attic. The surrounding attic structure seems to make the antenna behave as if it is close to physical ground, probably no matter how high off the ground the attic is.
     
    SM0GLD likes this.
  3. WD9DWT

    WD9DWT Ham Member QRZ Page

    For my coupled resonator antenna, I will be making home-brew wire separators by tieing the parallel wires to wooden tongue depressors using cable ties. And, I will report back on the final results!
     
  4. AK5B

    AK5B Ham Member QRZ Page

    Be sure to tell the elements to "Open wide and say ahhh" when you do so.;)
     
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  5. WD9DWT

    WD9DWT Ham Member QRZ Page

    The 40m ham-stick-modifed dipole works very well. With a 1:1 balun at the dipole and a short length of coax to radio room, the minimum SWR is about 1.1-to-1 and the 2-to-1 bandwidth is 125kHz. But I am having a hard time trying to find the optimum separation distance between the radiating dipole and the coupled resonator, which is a 31 feet length of 12-gauge wire. One web site suggested 2.5 inches of separation. Doing the math from equations in the Antenna Book yields 2.27 inches using the long method, and 2.66 inches with the short method. I tried all three, sweeping between 13 and 16 MHz, but the SWR is off-scale (> 6) in every case. The wire I am using is 12 AWG FLEX-Weave Bare tinned Annealed Copper Stranded.
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    Coupled resonator type antennas depend on the "driver" being full length and parallel to the parasitic element(s). Your driver is shortened by inductive loading. I would not expect that to work.
     
    AK5B likes this.
  7. WD9DWT

    WD9DWT Ham Member QRZ Page

    The coupled resonator does not work with the Hamstick-modified dipole. See my post and WA7ARK's post on Oct 9, 2021.
     
  8. WD9DWT

    WD9DWT Ham Member QRZ Page

    Yes, it actually works well. With a 1:1 balun at the feedpoint and a length of coax to the radio room, I get a 2:1 SWR bandwidth of 125 kHz.
     

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