Have You Heard of W5GI Mystery Antenna?

First of all, what is the mystery about this antenna? It was originally designed by John W5GI (SK). Now it is being manufactured by K4TR Antenna Mfg & Sales. It is a collinear array which resembles a G5RV, with good gain on 20m and it has 6 lobes of radiation broadside on that band. W5GI Mystery Antenna works on low bands with a tuner and is said to outperform a G5RV on 40, 80 and 160m.

According to IW5EDI, the mystery is that it is difficult to model and explain why the antenna works as well as it does! The antenna needs only two vertical supports which could very well be trees. One US ham told during a discussion on QRZ forum that it has been there for years at home on trees. Trees should be tall enough to permit installation of wires about 25 feet above the ground and 130 feet apart.

W5GI Mystery Antenna is a collinear antenna with three half wavelengths in phase on 20m and a half wave 20m line transformer. It has low feedpoint impedance so that it can be connected directly to the coaxial feedline. Quarter wavelengths of coax shorted on the outer end does the phasing. RG8X mini-coax has been recommended. Line transformer is a half wavelength ladder line. Output from the ladder line can be fed to a 50 ohms RG213 or similar cable. While a balun is not recommended, a line isolator between the twin lead and the coax has been recommended to minimize feedline radiation and stray RF problems in the shack.

Step by step instructions for homebrewing are available at the webpage of IW5EDI. The antenna can also be mounted in an inverted V configuration. The antenna covers from 80 to 6m with reasonable SWR. I am tempted to try it out but for the ladder line, which also can be homebrewed with some effort. My friends have home brewed ladder line using wire and pieces of drip irrigation tubing which is supposed to be UV protected.