Parallel Dipoles in the Attic

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

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1. K9URSubscriberQRZ Page

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

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2. WD9DWTHam MemberQRZ 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.

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3. WD9DWTHam MemberQRZ 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. AK5BHam MemberQRZ Page

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

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5. WD9DWTHam MemberQRZ 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. WA7ARKHam MemberQRZ 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.

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7. WD9DWTHam MemberQRZ Page

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

8. WD9DWTHam MemberQRZ 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.