Despite being a popular and productive way of simulating amateur radio antennas, another method of electromagnetic simulation makes use of the Finite-Difference Time Domain (FDTD) method.

Without going into too many details, the method divides up the simulation space into little cubes of volume. Then the next magnetic field values are derived from the current electric fields. Then the next electric field values are derived from the current magnetic fields. Repeat.

FDTD makes use of Maxwell’s equations to calculate the above fields. Being a Time Domain method, what follows shows a movie like display of what is happening in the antennas in super slow motion.

The cool byproduct of this style of simulation is we get to see a movie of magnetic and electric fields as power is applied to an antenna. The fields build up around the antenna and eventually fill the volume with energy. For both styles of hex beam antennas you can see after a few cycles how the parasitic element becomes energized. Once both elements are energized the beaming action takes place and you can see energy propagating forward.

Both simulation movies reveal the magnetic fields in the first 50 seconds and the electric fields in the second 50 seconds. They, of course, happen at the same time to yield Electro-Magnetic fields, but I could not show both in a meaningful way.

Here is a 10 meter Traffie (Classic?) Hexbeam…

Here is a 10 meter G3TXQ Broadband Hexbeam…

Neat eh?

No simulation technique is perfect, but the FDTD method’s ability to show EM in time is very cool.

If you are interested in FDTD, Google has quite a bit of information. There are some free tools out there for the taking.

I already have a post concerning my selection for the hex beam’s center hub. After reviewing the several aluminum plate styles offered by Leo, Hexkit and many others, I chose the molded Hex Beam Aluminum Hub by DX Engineering.

For wire I purchased 200 feet of 14 AWG Flexweave with Clear UV Resistant PVC Insulation. This wire is simply fantastic and has saved my bacon several times including at Field Day 2010 when I had to unravel the hex beam. My only concern is will it stretch over time and change the tuning. Time will tell.

So I had the hub and the wire. All I needed to finish the beam was spreaders and some rope.

I thought about the spreaders far too much. I read every post on the Hexbeam Yahoo forum. Many folks were using things like fishing poles, plumbing PVC and other locally available products for the spreaders. The consensus seemed to be fiberglass was the material of choice for long term enjoyment of the hex beam antenna.

Some folks said they found fiberglass poles locally. I could not. So I examined what Leo was using and saw Max-Gain Systems provides an appropriate kit of intersecting poles for both the Traffie style MW Hex Beam and Steve’s (G3TXQ) Broadband. I am not a cheap ham, but I did have a budget. After some thought, I realized I had already committed to Cadillac components starting with the amazing DX Engineering Hexx Hub. In about three seconds I decided to order the kit of poles from Max-Gain Systems and be done with the selection process.

Below are some photos of the arrival plus subsequent modifications and assembly of the Max-Gain Systems fiberglass kit. I needed some of the black rope also so simply added that to my Max-Gain order.

I cannot complain one bit about the Max-Gain Systems fiberglass poles. They just work.

Not discussed are the two 1 inch x 48 inch fiberglass poles also shipped by Max-Gain. One of these poles is for the vertical center pole of the antenna. The other is simply a spare pole that comes with the fiberglass kit. I wound up using PVC for the center pole and saved the other pole for future possibilities. However, I did make good use of the spare pole; I used some of it to reinforce the PVC from the bottom of the antenna to just above the hub. The 1 inch fiberglass tube fits perfectly inside 1-1/4 inch PVC. This allayed my concerns the PVC pipe would simply crush when clamped into the rotator and the PVC would buckle during rough handling. The fiberglass pole inside the PVC pipe provides a sturdy inner core.

I wish I could have run the fiberglass the whole length of my hexbeam’s center post, but the wire connection bolts prevent this. I am still satisfied as I think most of the stresses in the center post exist between the rotator and the center hub. PVC plus fiberglass core exist in this critical area.

I now have a portable (mostly) contest band broadband hex beam and it really does work pretty darn well.

This G3TXQ Broadband Hexbeam project exceeds my expectations wonderfully well.

One of the stations used an Elecraft K2 with an external power amp plus the 100 watt auto tuner. The Elecraft auto tuner provides two antenna ports. We connected a large dipole to channel 1 and left the other open for another antenna.

At some point during Field Day I decided things were going well enough for me to concentrate on my 20-15-10-06 meter hex beam of the G3TXQ variety.

As you can tell by the first photo below, the hex was hastily shoved into the trailer. However, I used good Flexweave wire for the elements and untangling the mess was straight forward. I decided the put the hex beam on the K2 station since it had the open antenna port and, for some reason, I think the K2 and the hex beam complement each other.

The hex beam was a bit loose in its rigging causing the elements to slump a bit. However, the thing tuned right up on 20, 15 and 10 meters similar to its debut during the Virginia QSO Party. Six meters was way off; I think the 10 meter wires were a bit too close to the six meter wires. No matter, the K2 had no 6 meters and 10 meters seemed to work well enough.

Results

Did it work? Boy it sure did. During my turn at the K2 Phone I found the hex beam provided two to four S units improvement against the dipole on 20 and 15 meters.

Late Saturday night I worked 4,800 mile contact with Hawaii (PAC) from Virginia with ease on 20 meters… on Phone! The Hex Beam and K2 bagged the only PAC contact of the four stations on site.

Several more 20 meter contacts were easily made to the West coast including LAX, SDG, SCV and WWA. I wish Field Day used Sections as multipliers, but I was glad to be able to add fresh contacts to the club’s totals. Tom, owner of the K2, quickly added many CW contacts using the beam.

The hex beam was up only about 15 feet and still worked quite well. Amazing.

We did have a rotator, but did not have it aligned with North. That was troubling, but I was just glad to be able to steer it at all at Field Day. We used a Channel Master TV type rotator. Yes, it works, but clearly is over stressed by the inertia of the hex beam despite its low mass. Anyone contemplating a rotator for their hex beam is well advised to “up” the rotator ratings quite a bit to ensure mechanical robustness.

Of all the compact compromise Yagi-Uda beam designs out there, I have to say the hex beam lives up to its own hype. There’s no magic in the hex beam (no matter what anyone tells you). It can’t outperform full size single band Yagi-Uda designs. However, for the investment, it is a superb value and deserves to be on anyone’s short list of antenna choices.

Choice Matters

The most important thing learned at this Field Day is having two antennas to select between makes a big difference in operating success. For some reason North Florida was alive with contacts and I sometimes used the hex beam and other times the wire dipole on 20 and 15 meters.

Yes, it’s Field Day and we tend to be minimalist. However, I designed this hex beam to be very portable and think it fits well with the Field Day theme with its simple tent peg tripod mount. It nicely complements a wire dipole.

The G3TXQ 20-15-10-06 meters Hex Beam antenna is a keeper for Field Days of the future.

Here is a picture.

Trailer Load for Field Day 2010

My finest hour this is not. It will do though.

Good luck with Field Day 2010 everyone.

John

If my plans included the 17 and 12 meter bands I would have purchased one of these kits with no questions asked. However, I felt my need for only 20, 15 and 10 meters (6m maybe) were not sufficiently addressed by the kits. Yes, you can get wiring just for these bands, but the cost differential was slight.

So I decided to custom pick parts for my own custom variation of the hex beam. The hub for the six fiberglass poles was a logical place to begin.

The hex beam has been around long enough to have a cottage industry to support it. Ever since the March 2009 QST article more manufacturers have emerged. The base plate suggested in Leo’s QST article and offered by most of the manufacturers use two U Bolts to hold each fiberglass pole. The HexKit.com baseplate is one example…

The Hexkit.com baseplate

The instantly obvious issue is the way these flat plate units hold the round fiberglass pole. The U-Shape of the bolt is good, but squeezing the round pole to the flat plate can easily stress the pole. This is easily circumvented with saddle clamps and other methods that have been around for centuries, but I guess the stress on these poles is sufficiently low to not be a problem. I did notice many hex beam sites reinforcing the poles in the hub area while others have welded metal pipes instead of clamps. Perhaps there is a problem with fiberglass poles against flat plates after all.

Last year when I started thinking about making a hex beam, I seriously considered purchasing just the aluminum plate and purchasing saddle clamps of the correct size from DX Engineering like this example…

DX Engineering Saddleclamp

The mechanical benefit over U-Bolts is obvious. That said, hundreds of amateurs have been carefully using the flat plates with perfect success so it appears the more proper saddle clamp approach is only marginally necessary. However, I like doing things the more traditional way and swore I would use saddle clamps when it came time to build my own hex beam.

Time passed and other distractions caused me to shelve the project for a bit.

Then lo and behold… DX Engineering decided to enter the hex beam fray. Everything about their hex beam offering seemed pretty much run of the mill with the sole exception being their hub and especially the way they connect the poles to the hub. Here is a close view of the pole attachment point…

Where the pole meets the hub.

Wow. This offers the benefit of a saddle clamp, but with the saddle running the whole length of the pole-hub interface. Brilliant.

The hub costs about the same as the offerings from other vendors so there was no real financial advantage of any particular model. The sole exception is folks who make their own plate from raw materials and trade their time for cash savings; Kudos to them. My time is worth a bit more than the hundred or so dollars hex beam hubs cost.

Needless to say specifying the DX Engineering hex beam hub in my design was a no brainer and that’s exactly what I did earlier this week. The web site said they were out of stock, but it arrived in a few days during a snowy mid-atlantic Saturday anyway.

I have purchased DX Engineering products before with the primary feature being excellent documentation. I decided to see if my Lego building seven year old could put this product together. Let’s see what happens…

The seven year old had no problems at all except for that V-Bolt moment.

So the DX Engineering Hex Beam hub is here and the project is officially underway. I patiently await the arrival of wire and rope from The Wireman and fiberglass poles from MaxGain Systems. Hopefully by March I will have my 20-15-10-6 meter contest band hex beam ready to go for the Virginia QSO Party.

So…

I have been eagerly absorbing all there is to know about the hex beam style of HF antennas.

If you are the least bit interested in building or buying your own hex beam a must read web site is the G3TXQ study of the hex beam…

One word that comes to mind is “WOW” what a great collection of tests, simulations and other thoughts about the hex beam.

My favorite feature of the site is the availability of an EZNEC simulation file for the G3TXQ of the five band broadband hex beam.

I eagerly downloaded the EZNEC file and, because I have the + version of the software with a higher segment limit, changed all the wires to a consistent and even segmentation rather than keeping the tapering feature. I now have 1223 segments in the mode. It takes a lot longer to do simulations, but is no big deal.

What I am doing with this beam is for another post. The question I hear often on the hexbeam Yahoo forum is concerning using the five band hex on 6 meters.

The focus of concern comes from the third harmonic of the 17 meter element which is close to the 6 meter band.

Indeed running a SWR plot on the stock five band hex beam between 48 and 56 MHz yields…

SWR of Five Band Hex Beam for 6 Meters

Hmmm, this is not a fantastic SWR, but sure suggests something in the five band broadband hex beam is absorbing the energy. Let’s see where the currents are…

Current Magnitudes in Five Band Hex at 51 MHz

Sure enough, the 17 meter element has the most current suggesting it is providing the majority of the absorption at 51 MHz. If you look closely, only the driven element has lots of current while the reflector seems quiet. If you look closer still you can imaging the 17 meter M element acting a bit like a folded Extended Zepp antenna. An examination of current phase indeed confirms that center current peak is of opposite polarity than the current peaks at the ends.

So this is all very interesting. The stock G3TXQ Broadband Hex Beam sort of works on 6 meters. Even if you can live with the high SWRs, is the pattern useful? The next figure shows the Elevation pattern of the five band hex beam up about 20 feet above the same ground as defined in the original G3TXQ file…

Elevation Pattern of 5 Band Hex Beam at 51MHz

Hmmm, not too shabby. Remember to not get too excited with gain figures of 8 dBi when simulating antennas above real ground; There is often a gain increase due to ground for any antenna including simple dipoles. The point here is this HF antenna seems to offer some gain at 6 meters. Here is the Azimuth plot of the 12 degree elevation…

12 Deg Azimuth of 5 Band Hex at 51 MHz

The front to back and front to side ratio is a bit weak at 5 dB, but this is certainly a directional antenna at 51 MHz.

My ultimate goal is to build a contest version of the broadband hex beam for just 20, 15 and 10 meters. After I deleted the 17 and 12 meter wires from the model, I ran SWR again to see if things change at 51 MHz…

SWR of 5 Band Broadband Hex Beam at 6 Meters

They sure did. The 12 and/or the 17 meter elements were certainly contributing to the dip in SWR in the 6 meter band. It is pretty obvious the 17 meter wires were operating at the third harmonic so I rule the 12 meter wires are not contributing to 6 meter operation.

So… what does the mean?

Two things.

1. If you have the five band 20-10 meter G3TXQ Broadband Hex Beam antenna, you may well have a workable 6 meter antenna too. If your rig has 6 meters on its HF output and a built-in auto-tuner, press TUNE at 51 MHz and see what you get. You may well have a free 6 meter beam ready for use.
2. Adding an additional 6 meter set of wires to the existing 5 band HF G3TXQ Broadband Hex Beam antenna, may be a waste of time since the 17 meter element is competing for some of the energy at 50+MHz.

The second point may surprise many folks who have invested in adding a 6 meter element to their five band hex beam. They say “it works fine.” That’s great, but it certainly is worth knowing why. In a future post we will simulate the five band with the extra 6 meter wires and see what we find.

Given the above facts, I will never add a 6 meter add on to the current G3TXQ Broadband Hex Beam design as it is clearly competing with the 17 meter antenna.

However, remember, I am building a three band hex beam with 20, 15 and 10 meters. This antenna won’t have the conflicting third harmonic issues caused by the 17 meter portion. I will explore the reasonableness of add 6 meters to my three band configuration in a future post.

Conclusion

For those of you with the 5 band design, you may well have a workable 6 meter beam an autotune button away from use right now. Give it a try and let us know the results by adding comments to this post.

There is an obvious conflict between an added 6m wire set and the existing 17m wire set which may create a complicated situation which looks “good enough,” but may be not what you expect. I would love to post your far-field 6 meter measurements of relative gain, front-back and front-side ratios. Please, no comments about how the hex beam is impossible to simulate.

Kudoes

I can’t thank G3TXQ enough for his extensive research into the hex beam antenna and his Broadband alternative. I very much look forward to building my contest version leveraging his excellent work.

Ever since the 2009 QST article many folks, myself included, became aware of the simple elegance of the Hexagonal Beam (also known as Hexbeam generally and Hex-Beam® by Traffie Technology).

Indeed the simulated and reported performance of these Hex Beam antennas appears to be quite reasonable for the size. The “hex-beam” group on Yahoo has been buzzing away with discussion.

Originally an organization called “Traffie Technology” offered Hex-Beam products.

Another vendor came along with parts and kits for DIY hex beams at HexKit.com.

Then the QST article in early 2009, written by K4KIO, highlighted a different topology inspired by G3TXQ where the size of the frame and arrangement of the wires differ from the classic Hex-Beam to yield more broadband performance on each of the 20-10 meter bands with the burden of slightly larger size.

Each Hexbeam “style” is covered in superb detail at G3TXQ’s web site…

So the hex beam nuts had two choices of hex beam products: The Classic Hexbeam from Traffie Technologies and the Broadband Hexbeam created by G3TXQ and offered by K4KIO.

One of my favorite amateur radio companies, DX Engineering, came out with their own kit version of the broadband hex beam design called the Hexxagonal Beam.

So now we have four major suppliers of hexbeam kits and/or parts…

• Traffie Technology with the HEX-BEAM®
• HexKit
• K4KIO with the G3TXQ Broad band Hexagonal Beam
• DX Engineering with their HEXXAGONAL BEAM (a version of the G3TXQ)

The various names are humorous. Only Traffie Technology has a registered trade mark on HEX-BEAM®. DX Engineering is trying to claim trade mark on HEXX and HEXXOGONAL using Copyrights which is a bit bizarre. K4KIO discusses trademarks/copyrights on his site very briefly. Two of the three web sites reveal a surprising lack of understanding of what Copyrights and Trademarks are. Oh well.

With four competitors in the Hex Beam supply biz, I suggest the Hex Beam has arrived. These companies know you are out there and are competing for your antenna dollars. Traffie Technology offers the original smaller hex beam where both the driver and reflector are in the shape of a W; Traffie’s web site has a tech section which may suggest the Traffie version is not the classic, but something slightly different and more broad banded. K4KIO has the terrific QST article bringing attention to the G3TXQ broadband design. DX Engineering provides an excellent engineering background to the G3TXQ design stemming from their years of many well engineered antenna products; They have a spiffy new approach to the center base plate.

Look at each of their web sites and you will see the points they make in an attempt to win you over. This has better engineering… This has fewer parts… This has longer history… etc.

Note about Antenna Simulations
Note that some of the suppliers above, and many amateur radio antenna manufacturers in general, argue their antenna designs are not possible to simulate correctly in today’s NEC and other programs. Traffie mentions this on his tech page. Arrow Antennas told me the same thing for something as simple as their 440 MHz Yagi beam claiming no simulation works for their antenna.

Simulation has its limits and the lower cost versions of the available NEC programs often don’t have enough elements to properly model up something like the hex beam antenna, but it can be done with the more capable versions.

If an antenna manufacturer suggests simulations don’t match reality they either don’t understand reality, don’t understand simulations or are hiding something. No modern antenna engineering is performed without simulations (and of course real testing) these days. Antennas far more complex than any seen in amateur circles, including the hex beam, are successfully designed on the computer first with great success. Any manufacturer thinking their design can fool a competently modeled simulation of same is suspicious.

This does NOT mean these manufacturers don’t produce good quality results as hard core experimentation can and does work. Edison was weak on theory, but strong on trying everything experimentally; Edison experimented his way to success on several projects. However, Tesla was strong on theory. Tesla’s AC power system won the battle against Edison’s DC power system even before the first wire was laid down.

The point is Antenna Engineers howl at the idea any amateur antenna has supernatural powers that thwart decades old simulation abilities.

Its all good news though
The good news is the Hex Beam directional antenna in almost any form gives good performance in a compact package. In the end, we are the real winners. Go get you one…