With an eye to the final cost I’ve built a good 20 meter monoband Hex Beam antenna.
Here is the progression of the project:
It starts with a base to work on. In this case I had some conduit in concrete from a canopy I no longer use-
For the spreaders I’ve used Tractor Supply Company TSC six foot driveway markers. I’ve jointed the markers with about 4-6 inches of aluminum tubing from Home Depot. Although I was able to find the tubing I needed the cost was high, almost $10 dollars for just a couple of feet.
This is the first problem I ran into- the spreaders fall from side to side. This racking problem root cause turned out to be the failure to pin the spreaders to the base. To save weight and cost I’ve used galvanized fence wire to tie the spreaders to the base. This is similar to how rebar it tied before a concrete pour. The solution is to drill a small hole in the fiberglass rod and pin it to the base.
Original plate design- ugly but many prototypes are.
Here is a close up of the drilled rod fixed to the base plate.
Here is the black iron pipe flange I chose for the build. I’ll update this post asap with the dimensions. It’s a happy coincidence that EMT tubing will fit almost exactly into the pipe threads. I trimmed a few thousands off with my lathe but am sure it could have either been driven home with a hammer or either the flange or pipe could have been filed slightly to allow the interference fit. I then welded the EMT to the flange for both top and bottom. The top flange has a short stub, about 8-12″ that with another happy coincidence standard PVC pipe fits over just a bit loose- a few wraps of electrical tape was used to fill this slight gap.
Here is a “worm’s eye view” of the base plate bottom.
Here is competed Hex Beam. I learned quite a bit from this first build. The measurements are critical as is the tweaking of tensions and lengths. It took MANY trips around to get the Hex even close to symmetrical. I’ll go into this a bit later in the post. The materials for the mast and PVC upright all fit very close- little work is required. The plywood base turned out to be too thin- though it seemed ok during the build after a week or so it warped. This is addressed in the second build. Even as such this antenna survived the tail end of Hurricane Arthur on a 30′ elevation.
Tree down from tail end of Hurricane Arthur. The Hex Beam 100 yards away had no damage.
Here is the Hex installed, there were many R&R’s- remove and replace sessions. Along the way I began to tie the spreaders together part way up the antenna to increase stability. The classic umbrella shape was affected at one point.
Finally, the SWR for this build- 1.08:1 inside the 20 meter phone band. I’ll take it. My design was taken from http://karinya.net/g3txq/hexbeam/broadband/ I chose to use insulated 14 gauge stranded wire. There are conversion coefficients also on karinya.net at http://karinya.net/g3txq/hexbeam/wire/
After the first build and many, MANY great DX contacts I attempted a design improvement. The plan was to add a second beam short spaced below the original beam. As such the gain could be as much as almost 2 dB based upon Yagi two element models. The build failed, the additional weight could not be supported with my economy fiberglass spreaders. Perhaps some day I’ll try this again if I can find a low cost solution. Same with a 3 element plan- the additional diameter would seem to require thicker fiberglass rods. The failure can be seen below.
The second build featured a double thick plywood base and fiberglass electric fence posts- these measure .375″ diameter. The earlier driveway markers measure .310″ diameter. The upgrade is significant. Unfortunately these are only available in 4′ lengths- no six footers as found with the driveway markers.
Similar to the first design the fiberglass rods are joined by aluminum tubing. As a design improvement I’ve pinned all couplings and dual purposed one pin the coupling as a tie point. As previously fence wire is used to fabricate in place of u-bolts and for these ties. I chose 12 gauge copper for one of the pins as it more closely matched the drill bit I chose.
The Hex Beam elements are affixed with a similar system- a horizontal hole through the fiberglass rods. I was cognizant of the hole’s directions as I moved my way from the core to the outside.
As I strung the elements I started with loose tie wraps then tightened as I approached the finish.
The spacers are made of the same 3/32″ black braided polyester / dacron cord I used for many projects. A 1,000′ roll can be purchased on Ebay for $39.99 from theropeguy1 shipping included. This is terrific rope to work with. Strong, knots well and un-knots well also…and is stealthy. All knots are taped over for safety- I STRONGLY suggest a 10 roll pack from Home Depot or Lowes before you start…and then another 10 rolls soon. Next to duct tape this is a staple.
Another design feature I’ve incorporated are these white markers denoting the Beam’s aperture. Once the Hex Beam is mounted it’s a bit difficult to see the orientation. These markers solve that problem.
The coax termination is CRITICAL. Keep the exposed lead length as short as possible. In my first prototype I found the SWR related to these terminations.
This is Rev 2 ready to install.
This revision features triple support for each spreader. This is probably not necessary if you purchase the “off the shelf” solution…but in my cheapo design these are critical. Balance the tension between all to they are even.
There is also an internal hexagon shaped truss system. These are cut and tied for each section- in theory the distance from the antenna center to the tie points is equal the the distance between spreaders at this point. In practice get them close and then tweak them for proper symmetry.
Instead of a 1:1 current balun I’ve opted for a choke coil- I use a washer fluid bottle and wrap about 7 times- there is no absolute on this. The purpose is to keep the coax from radiating RF that would distort the antenna pattern. I’ve never seen a SWR change from these chokes.
I’ve used a piece of tubing with a tape mark as a height gauge- as you turn the antenna the spreader tips should be similar heights. An inch or two off is ok, more than that and it will look odd. It will probably work just fine looking odd, but if you spend enough time you can get it looking pro. Keep in mind “enough time” is a euphemism for a period of time equal to your patience divided by 1/insanity. The tension of the leads to the terminal block should be snug, to adjust the height move the other spreaders, change the distance between the spreaders and the length of the top support cord. IT IS NOT EASY. Plan to spend many hours. Basically every time you solve a problem you make one somewhere else.
Spreader distance tool- This fiberglass rod with wire is used to rough in the spreader distances. It’s 128″ long and should be approximately the distance between the tie wraps where the element is attached to the spreaders. In practice this only gets you close- from there it’s “enough time”
The rotor is from Lowes, an RCA and cost just under $70 dollars. It’s probably too light for this but works fine so far. Below is a trick for easier installation- tape the clamp open. Trust me. PS The nuts are 11mm
Here is my present Hex Beam. It’s working great and looks much better than my first attempt. I have it about 30′ in the air. The difference between 20′ and 30′ was very small on the SWR graph- not sure about far field results. I have four guy ropes of the same material previously mentioned. The push up mast is EMT tubing with a black iron pipe stub welded inside on end to make male-female couplings. I have two sections on this project. In another area I have 3 sections and with guys it’s holding up just fine.
And the SWR? Oddly not as good as my first and uglier antenna…but not too shabby! 1.18:1 in phone band.
