Pros and Cons of HF Attic Antennas

In a perfect world, all hams would have plenty of room for antennas. HOAs wouldn’t exist, and there would be no need to hide antennas in the attic (provided you have one). While the performance of antennas located outside will almost always be better, locating them inside and in a roof space may be the only option—and a workable one.

Advantages of Installing an Attic Antenna

Though installing a radio antenna in the roof space won’t work as well as an outdoor antenna, there are some advantages:

  • Ease of installation: It is normally easier to install a radio antenna in the attic than outside. There is no need to climb up ladders onto the roof, scale towers, or raise tall masts from ground level. If you don’t like heights, this is a great advantage.
  • Access to feedline: All radio antennas need a feedline to transfer signals to and from the antenna. Coaxial cable is the most common form of feeder. It could be easier to route feeders when installing an antenna in the roof space or attic.
  • Protection from the elements: Radio antennas located outside are subject to weathering. Wind, rain, and pollution all cause the antenna to deteriorate over time. Even the coax can deteriorate quite quickly, especially when water seeps inside.
  • Visual impact: Antennas located outside can be unsightly. Locating them inside removes the visual impact and hides them from neighbors and the HOA.
  • No trees, masts, or towers needed:The support structure is already in place.

The Downside

Attic antennas are a compromise and may require more planning and care during installation. You should choose them only when outdoor antennas are impractical or not allowed.

  • Low height above ground: An antenna cannot be placed higher than the highest peak of the roof, a point usually low in terms of optimal HF antenna height.
  • Heavy metal: Got a metal roof, foil-backed insulation, and large amounts of HVAC paraphernalia? If you have any or all of these, the attic option may not work.
  • Shorter antennas: Sometimes the antenna must be shorter than 1/2 wavelength for a dipole to fit into the available space. Work-arounds include loading coils, traps, and linear loading—all of which can reduce efficiency.
  • RFI interference: Because of the proximity to your living area, interference from plasma TVs, power supplies, and other electronics could be a problem. You’ll need to neutralize sources of RFI that may interfere with your receiver.
  • RF exposure: Because the antennas are installed inside the structure, you need to consider RF exposure to yourself and those living in your household. Likely this will include adjusting transmitter power levels. The ARRL has a PDF document, “RF Exposure and You,” which can give you some guidance.

Attic Antenna Installation Tips

When locating an antenna in the attic or roof space, there are several precautions you can take to ensure that performance is the best for the circumstances.

  • Keep away from internal wiring and ducting: There is often internal wiring or HVAC ducts within the attic or roof space. Make sure the antenna is as far away from these as possible so they do not affect performance.
  • Remember wiring and objects from the floor below: When installing an attic antenna, it is easy to forget lights and electronic devices can be a source of considerable interference. Keep the antenna as far away as possible from these and take measures to reduce or eliminate RFI in the home. Also remember the opposite is true—wiring can carry interference caused by your antenna.

HF Attic Antenna Options

Confined spaces limit your options when it comes to HF antennas. It’s also assumed that performance is much less than full-sized antennas. Depending on the attic, construction materials and layout, this can be true. But as a general rule, the impact is not as great as you might think.

You can install a simple wire dipole in almost any attic space. Don’t worry if you don’t have the room to run the dipole in a straight line. Try to keep the first 1/3 of each wire starting from the feed point straight and in the clear. The last 2/3 contributes little to radiation, so you can bend and shape it almost any way you want, except for folding it back tight on itself. Cross other conductors, like wiring, at right angles when possible to minimize inductive coupling, which increases RFI and losses.

Want to work more than a single band? Parallel/fan dipoles are a good solution that will allow you to operate on multiple frequencies. They’re a relatively simple DIY project, or you can purchase a commercially made one like the Alpha Delta DX-EE, DX-CC, or DX-DD. All use Iso-Res coils for shortening and multibanding the antenna. The DX-EE is particularly attic-friendly with a 40-foot total length. Another dipole suited for attic use is the doublet, fed with ladder line and matched with a tuner such as the DXE WA-070.

Alpha Delta Parallel Dipole Antennas photo

Rotatable multiband dipoles are also a possibility, though they may not have enough room to actually rotate. They’re essentially short dipoles with traps or loading coils and constructed with aluminum tubing. Some examples include the MFJ 1769 (26 feet) and Comet’s CHV-5X (14 feet). Some of the shorter ones like the Comet may be able to rotate in some installations.

But it isn’t all about dipoles. You can try a magnetic loop—just remember it has a narrow bandwidth. Another option I discovered is a Broadband Butterfly Terminated Dipole (BBTD).,The BBTD radiator is a big loop that follows the perimeter of the roof. It’s a close relative of the Terminated Folded Dipole, using a balun and a terminating resistor. It is truly broadband, with loss on some lower bands but gain on 20 meters and above.

Mobile antennas such as hamsticks, screwdriver antennas, and others are already a compromise. Putting them in the attic makes them even less effective. Sure, you can try them, but the closer the antenna is to “full size,” the better it will work.

Up in the Air?

Attic installations will require you to spend some time trimming and tweaking the length of the antenna to achieve the lowest SWR. You won’t know exactly what will work the best until you build and test the antenna. That experience will help you—and maybe you’ll discover new options.

At least you’ll be out of the rain and snow. . .

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