Winter 2006 Issue

A Low-Loss, Low-Cost, Three-Element
Yagi Antenna System for 6 Meters


Take a little junk and a trip to the hardware store, add ingenuity, and what do you have? For K8VBL, the result was an antenna system for 6 meters for under $20.

By Tom Turner,* K8VBL/VP2VEL
 

For a cost of less than $20, a low-loss, three-element Yagi beam antenna can be built for 6 meters using components from local building and auto discount stores. Over 6 dBd gain can be realized, and the beam is light enough to be supported on a salvaged TV antenna tower and rotor. The following is a description of the 6-meter beam, tower, and rotor put up at K8VBL/KA8EHE.

Over the years, many 6-meter beams have been described in ham publications. Most of them use elements of 1/2-inch aluminum tubing. In a quest for materials to build a beam, a metals supply house was contacted and $60 for three 10-foot lengths of 1/2-inch aluminum tubing was the quoted price!

The high cost of aluminum prompted a search for less costly, locally obtainable element material. Our local building-supply discount store offered 1/2-inch (ID) thin-wall copper water pipe for less than $3 per 10-foot length. The advantages of copper over aluminum are that it is a better conductor and is easily soldered to provide low-resistance connections. Copper pipe is somewhat heavier than aluminum but appears to have about the same mechanical strength.

A gamma-matched coax feedline to the driven element was considered but was discarded in favor of a delta-matched ladder-type feedline for the following reasons. A gamma requires several connections, some of which are at low impedance points in the antenna system. Therefore, a few ohms of resistance in these connections will result in losses that seriously degrade the beamís performance.

A delta-matched ladder line requires only two connections, both at points on the driven element where its radiation resistance is relatively high, and provides a fully balanced feed to the driven element to minimize distortion of the beamís directive pattern.

Ladder line has 50% lower loss than coaxial cable at about one third the cost of coax. However, ladder line has the disadvantage of requiring extra care in installation, but by use of an ordinary TV-type lead-in bushing and standoff insulators, a completely satisfactory feedline installation is easily accomplished.

The low-loss, three-element Yagi antenna for 6 meters. (Photos by John Chandler)

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