Quadrifilar Antenna

Information about my Quadrifilar antenna built in April, 2003

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The Quadrifilar antenna is by far the best type of antenna for use in receiving polar-orbiting weather satellites. No other omni-directional antenna comes close. This is the type of antenna that is actually used on the satellites themselves for transmitting the images. I have now built two of these antennas. My Quadrifilar antennas were based on the Tall Narrow Quadrifilar Helix Antenna design by Steve Blackmore. When first starting out, building one of these antennas can seem somewhat daunting. Once I got started building mine I was determined to complete them both. I built the second one because, while my first one worked well, there was still some issues that I wanted to iron out. I found myself thinking about design improvements constantly, and finally had to build the second one to see if my ideas worked! My new antenna performs far better then I could have imagined. It seems to work from horizon to horizon in any direction with almost no signal loss.

Construction photos showing some of my additions to Steve Blackmore's design.

• I'm using clear Acrylic tubing over the copper helical elements for protection.
• Gray electrical PVC, instead of White plumbing PVC for the mast pipe. (Tapering at the top for easier soldering inside).
• Placing copper elbows inside for added support at the coax soldering points.
• Keeping the coax completely inside the mast until poking out for the balun, then sneaking back into the mast-pipe.
• The finished antenna propped up against a wall.
• Then antenna mounted on the roof.
• The view looking at the front of the house.
• After nearly five years of use, the antenna is really beaten up by the sun and rain.

Notice: I used dimensions given by the Tall Narrow Quadrifilar Helix Antenna design by Steve Blackmore. Although, I shortened his design on both "bottom" cross-supports by moving them up 50mm each. This makes the main elements "bow" out more then in his original design. My antenna looks slightly shorter and fatter then a true Tall Narrow Quadrifilar Helix Antenna. Most traditional Quadrifilar antennas are quite short and fat compared to the Tall Narrow design. Mine is only slightly shorter. This was to increase good coverage when the satellite is passing overhead. Often a null spot in reception for many Quadrifilar antennas. Other then that; my modifications are fairly minor to Steve's original plans.

UPDATE: November 02, 2007. After four and a half years of being attacked by the sun, beaten by monsoon storms and moved to three different rooftops; the old antenna is still going but not doing as well. I have taken it down a few times, rebuilt it once, but it still does not preform as it once did when new. Corrosion and rust has really taken it's toll and the internal connections I believe are failing at the copper joints. Attempts to seal and protect the easily corrosive copper tubing as over time failed. HERE for original antenna right after it was built, and HERE for after nearly five years of being out in the elements.

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This Page Last updated: November 02, 2007