Wednesday, February 25, 2009

The Hexagonal Beam Antenna, Bob, session 40

Today's Net was prompted by an article in the March 2009 QST. It discusses a variation on the hexagonal beam antenna designed by Steve Hunt, G3TXQ. I like this antenna and think it will make a good one for my rooftop. I intend to build it this Spring and install it this Summer. I will have an update when it is up.

The hexagonal beam antenna is a variation on the Yagi. It is essentially a two element Yagi, just the driven element and the reflector, where the elements are not straight. Instead the elements are bent in the zigzag shape of a W. I will refer to the top or bottom of the W. By that I mean the top or bottom of a letter W on a line. The bends are horizontal so from the side it looks flat. Looking down from above, the driven element radiates toward the "bottom" of the W. The top of the W of the driven element is toward the center of the antenna. The reflector is essentially the shape of the driven element but facing the opposite direction and of course behind the driven element. So from above it looks like two W's, one upside down and on top of the other.

This arrangement makes construction of this antenna easy. What you do is create a base that holds six spreaders radiating out evenly at 60 degree intervals, like spokes on a wagon wheel except that you use somewhat flexible spreaders and put tension on the ends to bend them upward so they look like an upside down umbrella. The antenna elements can then be made by stringing wire either from tip to tip or along the spreaders. Trying to explain the construction would be too difficult for this net. Look at the blog to get links that explain it with diagrams.

This is the original Hexagonal Beam. The QST article discusses a modified design by G3TXQ. In that design, you use the same basic construction but instead of the reflector being in the shape of a W, it is in the shape of an arc. This design was arrived at by experimentation and by using the design software, EZNEC. The resulting design is slightly larger, 21.5 feet diameter for 20 meters vs. 19 feet, but it has much better SWR characteristics over a broader frequency range as well as slightly better gain and a better front to back ratio.

These can be nested to create multiband antennas without the need of traps. This is similar to the concept of a multiband dipole that consists of dipoles cut to each band that are connected at the feedpoint.

LINKS
HEX-BEAM by Traffie Technology
A homemade Hexagonal Beam in 3 hours
Good Site on Original and G3TXQ Versions

2 comments:

steveeh131047 said...

Bob,

Good luck with building the broadband hexbeam. If you have any queries PM me, or post on the Yahoo Hexbeam group - I monitor it pretty regularly.

73,
Steve G3TXQ

Ron W4RDM said...

Bob,
Let me know if I can be of any help. Antenna building is one of the final frontiers for the homebrewer in Amateur Radio. A hex wire beam can be built for ~$350 to ~$400

73,

Ron W4RDM
www.hexkit.com