This last year I built a homebrew HexBeam. The commercial version of the hex
(see www.hexbeam.com) by Mike Traffie was a little too steep for my pocketbook, so
I decided to try to build one myself. My prototype version was for 20 meters.
I made it using 10 ft sections of PVC water pipe. The antenna worked better
than I had expected but was structually weak and I decided to try something else.
I was lucky to have a local ham friend who had some quad spreaders that he had never used and was willing
The quad spreaders were 13 feet long. I cut them to 11 feet, which was longer than I needed but allowed me to cut at points where the fiberglass poles had been made thicker for strength. I slipped a length of of vinal flexible tubing over the hub end of each spreader. This allowed me to tighten the U-bolts without worrying about cracking the fiberglass. The spreaders were orignally a sort of mustard color. I spray painted them a flat gray to make them less conspicuous. I cut a slot in the small end of each spreader. With the cuts positioned horizontally, I marked the top of the big end of the spreaders with a black marker. This helped me duing the assembly, since I didn't want the slots to be vertical.
Unlike any other Hex beams that I know of, my hex does not use the wire elements as structural parts of the antenna. The elements are strung loosely within the "cage" made of fiberglass spreaders and dacron cord lines. The dacron runs around the perimeter of the hex and also from each tip back to the hub. When stringing the hex it is very helpful to remember your high school geometry. The straight line distance between the tips of an equilateral hexagon is exactly the same as the distance from the center to one of the points.
Here you can see one of the elements attached to a spreader. I used at wire-tie and some duct-tape to keep things from slipping. The element is not holding the spreader in any way. You can see in the picture that the wire, which is a stripped #14 wire from regualar "Romex" house wiring, is not tight at all.
Here you can see how I decided to maintain the proper tip spacing. I made up a triangle using dacron line with the correct dimensions (see below) and attached the wire to it. My antenna covers two bands. For the 20 meter element shown here, I made loops in the end of the elements for attaching the dacron. After reading W4RNL's comments about similar antennas on the web, I decided that the loops made the elements appear to be "thicker" and the ends and probably were adversely affecting the tip coupling. So for the 17 meter section, I used a different method. I put about 8 spots of a good silicone sealer along about 6 inches of the end of the element and the same number on the end of the dacron line. It let the silicone dry and then I then laid them over each other and used electrical tape around them. The silicone spots keep them from slipping apart.
It is important to note that the two elements in my Hex are fed separately. A coax runs from each to the shack. It is possilbe to use one feed line, but it is much more difficult to get the elements' lengths adjusted. Here you see the hub of my 17 meter element. Also note that the center pole of my hex is not a hollow PVC or fiberglass tube as is usually the case. I used a solid 1 5/16" wooden "closet rod". Most homebrew hex-beams and the commercial version have the feedline run inside the center post. For the 20 meter element I had slipped a piece of pvc over the wooden center post and tied the elements to the pvc with nylon line. This made the center points of the director and reflector wires further apart than they were in my computer model which had them only about 1/2 inch apart.
For the 17 meter hub I did something a little different that seems to work very well. I found a small rectangle of plexiglass about 2 by 3 inches. I drilled holes in the plexiglass for the wire elements. For the 17 meter section, I wanted to maintain the spacing between the driven element and the reflector that I had used in my computer model of the antenna. That is why I tried the plexiglass. I attached the small plexiglass rectangle to my wooden center post with a small length of wire which I ran through two holes in the rectangle and around the post. I worried that putting the hub off-center would adversely affect the results, but can not see that it has done so in any measureable way.
Here you see my Hex in the air. This picture shows it with only the 20 meter section mounted. You can just barely see a small coil of coax made into a choke balun just below the feed point. The antenna is turned by a small Radio Shack TV rotor. It only weighs about 10 pounds and because it is symetrical it does not tend to swing much in the wind. The 20 meter section is about 28 feet off the ground. The pole it is on is made of PVC sewer pipes that telescope. It is a "tilt-over" arangement, which makes raising and lowering the antenna for changes fairly easy. I would not recommend the PVC route, however, since it is really not rigid enough. I am fortunate to have a very high spruce tree nearby and have a rope over a pulley up in the tree that I use to help pull the pole erect. Without the help of the rope from high in the tree, the pole bends way over.
Below you can see the dimensions I used for my hex. I want to credit Dl7IO's webpage for infomation on the dimensions of the hex. I also recommend anyone interested in building a Hex check out the hex-beam group on yahoo.com. If you would like to contact me about the antenna write me at W1GQL(at)midcoast.com. Use "@" in place of the (at) which is there to make it harder for spammers.
Here is an EZNEC far field plot of the output of the 20 Meter
Here is an EZNEC SWR sweep of the 20 Meter band.
Caleb Wright, WA2JJX, recently built a homebrew Hex using bamboo spreaders. He used many of my ideas and added some clever ones of his own. Click here to read about his antenna and see a picture
Here is information of how to construct a common mode choke balun for the antenna if you find it necessary.
For 3.5-30 use 10 feet and make 7 turns.