The quadrifilar helicoidal antenna - quite a mouthful - is easy to construct, and the results are excellent. In contrast with the omnipresent turnstile antenna (two crossed dipoles with a reflector) the circularity is almost perfect in any direction.

In it's original form, the relation between diameter and height is 0.44, but decreasing this relation slightly, a still better coverage of for satellites near the horizon is obtained. In literature and on the web, extreme versions can be found.

Here are images of the quadrifilar (QFH for short) for reception of meteo satellites in the 137 MHz band. I was always convinced that this was a large antenna - it's not! Note: these images are not photos, but images generated with a 3D raytracing program (pov-ray).

The image shown is a QFH on board of the NOAA-17 spacecraft (photo courtesy and (c) of Lockheed Martin)

And here some real photographs of the construction process.

The first version was constructed using coax cable as a conductor. I was tempted to make a 'better' version using copper tubing. The results are very similar, and probably doesn't justify the extra work and problems that can appear if one's workshop isn't equipped for bending the pipes. Here, are some pictures of this version.

If there's interest in this last version, send me a mail - I can add a few drawings to clear up some undocumented items.

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(c) John Coppens ON6JC/LW3HAZ

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