Hex beam
| Hex beam | |
|---|---|
| Type | Two-element directional wire beam |
| Shape | Hexagon of wire on six fiberglass spreaders, like an upturned umbrella |
| Typical bands | 20, 17, 15, 12 and 10 meters, often with 6 meters added |
| Elements | A driven element and a reflector for each band |
| Performance | |
| Gain | Similar to a two-element Yagi |
| Polarization | Horizontal |
| Feed | Single coax for all bands |
| Turning radius | About 11 feet for a design that includes 20 meters |
A hex beam is a lightweight multiband directional antenna for the upper HF bands. Seen from above it is a hexagon: six fiberglass spreaders rise from a central hub like the ribs of an upturned umbrella, and wire elements for each band are strung between them. Each band has two elements, so the antenna behaves much like a two-element Yagi, but it is far smaller, lighter and easier to turn. A typical hex beam covers 20 through 10 meters, including the 17- and 12-meter bands that many trap tribanders leave out, and some versions add 6 meters.
How it works
Each band in a hex beam has a driven element, connected to the feed line, and a reflector, a slightly longer wire that is not connected to anything. As in a Yagi, the reflector picks up energy from the driven element and reradiates it so that the two add in one direction and partly cancel in the other, which produces gain toward the front and a reduced signal toward the back.
The difference is in the shape. Rather than running straight, each element is bent around the spreaders into a shape like a W or an M, so its ends reach toward the ends of the other element. The tips are close enough to couple to each other, the same idea used in the Moxon rectangle, and that coupling gives a compact two-element beam a good front-to-back ratio and a feed-point impedance close to 50 ohms. The elements for the different bands sit at different heights on the center post.
The version most built today is the broadband design published by the British amateur Steve Hunt, G3TXQ. Its element shapes keep the SWR low across the whole of each band, and the driven elements for all bands share one feed point, so a single run of coax serves every band with no traps or switching. A common-mode choke at the feed point is normally used.
Strengths and limits
The hex beam's appeal is its size and weight. A five- or six-band model often weighs well under 30 pounds, presents little area to the wind, and has a turning radius about half that of a full-size three-element 20-meter Yagi. It can go on a roof tripod, a push-up mast or a short tower with a light-duty rotator, and wire and fiberglass are less conspicuous than aluminum tubing, which can matter under antenna restrictions.
The trade-off is gain. With only two elements per band, a hex beam has about the gain of a two-element Yagi, a few decibels over a dipole, and less than a three-element or larger monoband beam. Covering 40 meters would make it much larger, so most hex beams stop at 20. Wire tension and spreader condition need occasional attention, and heavy ice or very high winds can break spreaders.
Building and installing
Hex beams are sold complete or as kits, and many hams build their own from published dimensions. The wire lengths and the spacing at the element tips matter: small errors shift the resonance and spoil the front-to-back ratio, so builders measure carefully and tension the spreaders evenly.
Like any horizontal HF antenna, a hex beam works better higher up. Even at modest heights, though, its directivity helps on receive by reducing noise and signals from behind, and its ability to be turned makes it a popular choice for DXing, contesting and Field Day stations.