|
For many weeks I collected all the bits and pieces needed to construct my own hex beam. As I did not have a ready source of fiberglass spreaders, I chose to use short pieces of narrow garden-stake bamboo fastened into longer lengths (10') using standard hose or "gear" clamps. It worked just fine, although the installation was not what anyone would consider permanent. Below, you will find lots info and anecdotes -- there's an introductory section, the construction section, and closing thoughts. Hope this helps someone build a hex, or decide to buy one of Mike Traffie's commercial, ready-to-go models that will work properly right out of the box. When I built it, I was convinced this is the best antenna for its size, weight, visual impact, cost, and installation requirements. The spider beam with three interlaced full-size monoband yagis, may outperform the hex, but it has fiberglass arms that are each 16.5 feet long (that's a 32-foot boom). The hex has a smaller footprint and works well. The
Bamboo Hex In March 2002 I started planning the construction of a five-band hex- style beam. Thanks to homebrew inspiration from VK2DPD, DL7IO, AA5HP and others, and Mike Traffie's outstanding concept and pioneering work, I managed to cobble together all the parts and ended up with something that radiated nicely from just a few feet above the roof. This
is a home-made five-band antenna made from bits of bamboo, some Please note that I consider this a "hex-style" antenna. I don't want to call it a "Hexbeam" as it is a pale imitation of Mike Traffie's real antenna. I was bitten by the contesting bug in 2002. G5RV antennas are great for casual operating, but they don't put you in the top half for many contests. I wanted something very cheap with at least a little gain that can be generally pointed at stations but doesn't need a tower (one day, I tell myself). The hex-style antenna met those requirements perfectly. Does
It "Play?" Signals in the hex's direction on 20M are often markedly stronger than on my G5RV, and readability is much better thanks to the lower noise. Claims
Sure to Get Me In Trouble With Experts After installation, the log looked like this: Date-Z
RX kHz Call RST S RST R QTH
& Notes 14-Oct
14042.6 CW 9M6AAC 599 599 East Malaysia Let's try the antenna in real-time. Unscripted. Let me run to the rig and see what I can work on 20M right now (10:20 p.m. local, Oct 16, 2002). Be back in a sec.... OK, took less than five minutes to find and work FO0PT on 14.044 at 0524Z. That's Moorea, French Polynesia, on three bands in two days with he hex. We were only 559 both ways this time, but made it work -- first call as he changed from simplex to QRX up 1. The hex was only about 1 S-unit over the G5RV for that QSO, which is only a "so what?" if you don't care about S-units. I did lots of quick A-B comparisons between the Hex and the low G5RV (doublet, 102 feet). Depending on where the Hex is pointed, I saw a full 4 S-units (from S-3 to S-7 or more) difference in favour of the hex. Some signals all but disappear when switching from the Hex to the doublet. And, honestly, some signals are better on the doublet (can't turn it, though). This may only be a compromise two-element beam, but it really is a dramatic improvement over all the other wire antennas I have built. It's not always exhibited, but when the conditions favor this antenna it is stronger than I thought it would or should be, even at my below-optimum height of 25 feet at the 20M element. Now, let's get into the construction effort.... Getting
the Parts
All of the above was or can be purchased from Home Depot. In truth, I spent around $150 on parts, including now-discarded materials for all the failed versions of the antenna. Things
I Tried But Discarded I "bend tested" some 10-foot pieces of dowel at the hardware store when no one was looking. They made a bit of a crackling sound at about two feet of arc. I purchased the two I tested (see the previous paragraph), but I didn't want to spend $7 each for six of them only to have them snap when I strung the wires. Next, I tried using six-foot lengths of thin bamboo stakes -- the "green" painted type from a garden center. Strapped together with hose clamps, these spreaders worked a bit but were still a bit too flexible and tended to arc too much to get the right shape. Combining the PVC with the thin bamboo didn't work at all, so I started over. I finally went to much stiffer five and a half-foot lengths of yellow bamboo -- approximately 1/2-inch diameter or slightly larger -- and joined with hose clamps where four or five inches overlapped. I worried that spreaders just 10 feet long would be too short, but I ended up cutting a foot off them anyway, after the wires were strung. The antenna goes together fairly quickly once the parts are on hand. I know I reinvented the wheel several times, and learned some tricks that I want to pass on to others. The construction details are a very long bit of text, but I know I would have appreciated a step-by-step tutorial when I started out. The
Center Hub Drilled holes for the U-bolts along the six 60-degree radius lines around the hub. Two holes per U-bolt, and two U-bolts per radius line. I couldn't find a protractor or my adjustable set-square anywhere, so I downloaded a graphic of a protractor from the Internet, printed it out and used that to make my angles. It's good to be a ham :) Drilled the center hole -- in my case 1 1/2-inch diameter to fit the pipe I am using. One of my big unrecorded expenses was for a hole-saw drill bit, as I didn't have one on hand. If you don't, ask your neighbor if he has one -- at $8 to $20 they are very expensive, considering you may only ever need it for this one hole. After buying one, I found out my father-in-law had an entire set of hole saws. I have now permanently borrowed that set, hi hi. Loosely
installed the U-bolts. Using a long piece of 14-guage common house wire, I fished the brass bolts down the tube into the holes... for the five-bander, this is 15 bolts. Took me nearly two hours to get them all in, and tightened up with one nut each. Make an eye-hole in one end of the house wire, slip the bolt into it and push it down the pipe till it pops into the hole you want. Then carefully thread on a nut. Once the nut is on a few turns, you can give the wire a good tug to release the bolt. Viola! Now just tighten the nut all the way, and glue it so it won't come loose. To secure the nut, I used a big drop of "Krazy" glue, making sure the glue flowed over the brass nut, and onto the PVC tube around the nut. The nuts are very well secured to the bolts and the PVC pipe so far using this trick. If I ever have to remove the bolts, I am sure a wrench will easily break the glue's grip.
The
Feedline Then I measured to the 17m bolt and made another loop, tinned it, and so on for each band. Then I did it again for the bolts on the other side of each band's driven element. Later, I used plastic tie-wraps to pull these wires close together between the bolt pairs. Why pull them together? Search me. It just looked prettier. And I suppose it lowered the impedance of the wire pair but I don't know what effect, if any, that has had on the antenna.
Install the spreaders on the hub with the thickest ends of the bamboo touching the PVC center post. Tighten the U-bolts. Now it's starting to look a bit like the expert versions of the hex beam. You, sir, are a genius. And you will tell your wife this several times before the elation wears off and you have to start stringing wires.
I knew from reading other reports that the basic 20m element leg length is around 9 feet 3 inches on a side. I cut a nylon cord 18 feet 8 inches -- that includes 2 extra inches for the center post's diameter. NOTE: the cord is even a few inches longer than this to allow room to tie a loop knot in each end. Connect one end of this cord near the end of one spreader, then string it to the 20M bolt of the center pipe, then across to the opposing spreader. You will know you have the correct points on the spreaders when both these spreader arms bend up and the nylon cord forms a flat, perfectly level line from one arm to the 20M bolt to the other arm. Ideally, this first cord would pass through a hole drilled in the center post at the level of the 20M bolts. Because I am lazy, I just tied a loop in the middle and hooked it onto the 20M reflector bolt. I put a hose clamp near each spreader tip and looped the cord around these clamps, allowing me to move the connection up or down until the line was level with the 20M bolts on the center pipe. I was pleased to see that the spreader arms had a very nice, even curve. The bamboo arms were working just fine so far. Proudly, I informed my wife that she was married to a genius. Then promptly scalded myself with the soldering iron. The
Wire Elements Once again, I used element lengths as described in DL7IO's excellent PDF tutorial. Because I was using speaker wire, which has a clear plastic insulation, I knew my wires would be too long, but cut them to DL7IO's lengths anyway. I soldered eyelet connectors to the ends of each wire. Start connecting the first set of elements -- the 20m wires. Attach each wire's eyelet connector to the appropriate (20M) center-post bolt and secure them with nuts. From the center pipe, the wire goes to it's nearest spreader tip, then to the tip of the adjacent spreader. When they're all in place, you will have two "W" shapes -- the reflected W beam. The hose clamps for 20M should be at the same point on each spreader as the hose clamps for your initial across-the-span nylon cord. As I installed these hose clamps, I used short pieces of plastic tubing (junk box stuff I didn't even know I had) and tie-wrapped them to the hose clamps. The element wire goes through the tubing to reduce the sharp bend at the spreader connection points. With all the 20M wires in place, you can start pulling together the ends of the reflector and ends of the driven elements. Try to keep the spacing at about 8 to 10 inches, to start. I have used VK2DPD's trick of soldering a brass washer to the wire, about two feet from each end and tying a nylon cord from one washer to the other leaving the wire free to trim as necessary. I had to trim about eight inches off the original driven element length, and the same off the reflector, to get resonance. The DL7IO PDF file has exact spacing for the wire tips. I haven't been able to duplicate them all properly. The
Smarter Way Loosen all elements for all bands. Tension the 20M band by itself, at whatever wire length you have. Get the 20M driven element close to its resonant length (I had to go by SWR), make sure the reflector is 5 percent longer, and tie nylon cord between the tips, using the spacing recommended by DL7IO. Once this is done, tension the wire to the spreaders again and allow the element lengths to dictate the correct position of the hose clamps on the spreaders, keeping the elements level across the feedpoint at the center post. With this "master" curve geometry established, repeat the process for each of the other bands. For simplicity, I wasn't too concerned about the interaction of one band on the others, just tuning and stringing up each band as I went. If the curve geometry is all right, wires for each band should naturally find their own spot on the spreaders, keeping level with their feedpoint bolts. Mine seemed to be pretty close, but not perfectly level in every case.
I made a coax RF choke by making six turns of coax just four inches in diameter. A larger diameter (five or six inches) would be lot better, though. I ran the coax down the side of the pipe, between the driven and reflector bolts, using tie-wraps to secure it at top and bottom. I have run about 70 feet of RG58 to the rig. It's small coax, but the only long cable I have on hand. I was overeager trimming the 20M wires, and they were too short at first so I soldered more wire back on. Most of the other elements are a bit long and were resonant below the bands when on the ground, but the antenna appears to be extremely widebanded [Resonance went up a bit with the antenna up on the mast, and all is fine]. My rig is an FT-920 with on-board tuner. So far, I haven't had to use the tuner with the hex, except on 10M. The SWR is that good. I measured SWR across each band, but here are the readings for the areas I'm most likely to centre on: 14.050
Mhz 1.4:1 I scavenged 100 feet of rotator cable from my father-in-law, who moved from an old satellite system to the newer DSS stuff (so not rotating needed). The Archer rotator went up and turns things just fine, although we'll have to see what the first windstorm does. The mast system is two 10-foot sections of chain-link fence top rail, plus a couple of feet of thick-wall PVC stub mast between the rotator and antenna. I drilled a hole and bolted through the "swaged" join of the two metal mast pipes to stiffen the connection in the middle, but it is still a bit rickety for comfort. Will add a splint of some sort around this join to strengthen it. The mast foot is on top of a three-foot-high concrete retaining wall near the house. The pipe is strapped to the lower part of the house's gable-end at about 15 feet high. Our lot is tiered from the back of the house down to the front, so half of the antenna is always about 25 feet above ground level, while the other half is about three feet closer to ground. Putting
It On the Roof Sadly, the house still badly needs painting. This is because I had this antenna thing sitting in the driveway and there was no sense painting till that was up in the air. Seeing had a ladder handy, a few weeks ago I put up a mast made of three sections of steel fence rail -- 30 feet in the air to support one end of a half-length 40M-to-10M G5RV. (My 102’ G5 is between two maple trees at the back of the lot). On antenna-raising day, I took out one section of the mast, so the rotator was installed at 20 feet. This is actually 23 feet over ground for half of the antenna, as the mast stands on top of a concrete retaining wall between the elevated back lawn and the driveway. The rotator is about five feet above the roof (I think that may be too much unguyed height for the fence-rail pole, but we’ll see). I put up one section of pole with the rotator bolted on top, letting it all hang in the bracket bolted to the lower end of one gable. Once the antenna was installed, I would push the bottom section of pole into the top section and push it all the way up to full height. The trick was: how do you get a 20-foot diameter antenna up onto the roof? The answer, I thought, was to get the lovely XYL to hand it up to me when I was half-way up the ladder, then carry it the rest of the way. This worked OK, but once I had the antenna sitting on the roof, I didn’t have enough leverage to actually raise it the extra six inches to plop it into the waiting rotator. So, naturally, I dropped the antenna from the roof on my first attempt at putting it up on a Friday evening. Just couldn’t quite control it as I was lifting it into the rotator, and over it went. The XYL helped save it until a good neighbor (hearing my cry of “Oh darn*! It’s falling!”) came running to take it from her.
Fortunately, the 20M wires snagged on top of a wooden fence, preventing the antenna from hitting the ground. I really thought the antenna would be busted to pieces, but I soon discovered that it was just fine. The XYL was all right, too, “and thanks for asking so quickly,” she added as I examined the antenna again. I told her I was badly shaken by the incident. It was all I could do to work the Oceania CW contest, the NA RTTY Sprint and the PA QSO Party over the next two days using the lowly G5RV, mulling over a better way to get the hex antenna safely into place. It took until Monday morning to get the courage to climb the ladder again. From around the corner of the house, where the ground is three feet closer to the eaves, it took just five minutes to hoist the antenna, using a rope slung over the top of the extension ladder this time, and get it into the rotator. Don’t try doing this alone, no matter how anxious you are to get the antenna in the air. Even 20 pounds of ungainly wire and bamboo can be dangerous if it gets away on you and pulls you down with it. It is exciting to have this homebrew antenna in the air, and having my first-ever rotatable antenna. Some might think the contraption is ugly. My good neighbor commented, “you can talk to Mars on that thing.” A co-worker viewing my “baby” pictures of the antenna noted, “it looks like an upside down umbrella.” My wife looked up at it and said, “Honey, the house badly needs painting.” Sure, it has slightly warped spreaders, and the wires are not totally symmetrical, and there are other obviously homemade irregularities -- but to me it is a beautiful thing, close enough to perfect. Next
Time The bamboo and bright copper speaker wire really stands out in the sunlight. Though the neighbors haven’t said anything yet (they live above and behind us), I’d rather not intrude on their view needlessly. I will paint the spreaders, hub, and center post either mottled gray, or flat black for low visual impact. Don’t know if I’d use speaker wire or common solid house wire next time -- the speaker wire is pretty heavy with its thick clear vinyl insulation. Might use the bare ground wire from house wiring instead, and just paint it. Why hang all that heavy insulation? Hopefully, the uninsulated wire won’t be as electrically long as the insulated speaker wire and need less pruning. Your
Mileage May Vary Although I am pleased with what I've built so far, I think I got lucky with my element pruning. The results of YOUR hex-style beam will probably be even better. And my results will only get better as I work on it or build the next version. My project shows that a hex-style beam can be built using very cheap materials -- bamboo sticks and plywood. It won't last for years without frequent care, but it's very sturdy. Twice, wind storms blew over my lousy test stand (two and a half concrete blocks and a bit of 6" PVC). Both times, the antenna fell from 14 feet. The spreaders hit the ground and a fence without a scratch. The thing weighs 20 pounds or less, and seems to love the wind. If
you don't have seven months and two young sons to help build one, Thank you for reading, and please let us all know how your own project is going by joining the Hex Beam Group on Yahoo! Latest
Antenna Overview 40M
Rotatable Dipole Project 80M
Wire Vertical Phased Array Project My
Hex Beam Project Spider
Beam Group on Yahoo DF4SA
Spider Beam Site
|
