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.

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.

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…

All three antennas are shown below with the relative currents displayed.

All three antennas at 10 meters

Since 28 MHz is so short, the current profile along 43 feet of vertical radiator is long. The SteppIR BigIR in 3/4 wavelength mode shows a full half wave of current high up along with the 1/4 wave at the bottom. This is, of course, the definition of 3/4 wave. Finally the simple 1/4 wave vertical mode is on the right.

Here are the three patterns superimposed…

Elevation Gain Plots of 43' and SteppIR BigIR

The following characteristics are revealed:

• The 43 foot vertical has its peak lobe at 56 degrees with gain of 5.6 dBi
• The 3/4 wavelength mode of the BigIR has its peak lobe at 47 degrees with a gain of 3.9 dBi
• The 1/4 wavelength mode of the BigIR has its peak lobe at 27 degrees with a gain of 0 dBi
• Suprisingly, the SWR calculated from 28 to 29 MHz was well under 2 and often under 1.5 for each antenna

This comparison reveals each can work at 10 meters, but one has to argue the 43 foot antenna’s angle of radiation is a bit too high for practical use.

The 3/4 wave mode of the BigIR edges out the 1/4 wave mode just slightly at the low angles we desire for long haul DX. Still, who knows, you might gain some benefit from the 3/4 mode if your soil conditions and location are different and the BigIR lets you choose either. Another way to look at the 3/4 mode is a large half-wave radiator is somewhat elevated which may help clear obstacles close by; That could be a serious benefit over 1/4 wave. Pretty nice.

Next time we will analyze the 12 meters band the same way as above and keep going until we hit 160… or maybe just 80.

Stay tuned to your RSS feed.

For some while SteppIR has offered two vertical versions of this adjustable length antenna: one for 6-20 meters, the other 6-40 meters. Also, an optional base load coil option is available to extend band coverage to 60 and 80 meters.

The web site…

…offers an excellent view of what is inside the control boxes of the BigIR Vertical and the 80 meter coil.

You get an instant appreciation of how SteppIR Antennas, Inc. has addressed how to make an antenna element move in and out in an almost infinite number of positions using a stepper motor.

The 80 meter optional coil is also a clever way to extend the capability of this antenna to the lower bands albeit with compromised performance indicative of any “electrically short” radiator. This is, of course, due to antenna physics, not anything SteppIR Antennas, Inc. did.

The manufacturer’s web site…

…also shows a photo of the inside, but which does not immediately reveal this is a custom PCB switch using a PCB .

The 80 meter option assembly is very large and I began to wonder why.

Because the 80 meter option is a tapped inductance, as clearly shown in the photos contained in the web site referenced above, one might consider using high quality RF switches or relays to select the amount of inductance. A switch to bypass the coil entirely when using the SteppIR BigIR for 40 to 6 meter work is also sensible.

What the photos on the web site above made clear is SteppIR Antennas did not use RF relays to perform the select-coil-tap function, but manufactured their own switch using printed circuit boards arranged in a rotating contact switch operated by a stepper motor. Obviously, they are capitalizing on the great experience they have with stepper motors and the way they control it with their desktop controller.

As noted by the fine folks on the SteppIR email list, the coil taps have potentially large voltages that could easily arc over relay contacts when operating at higher powers.

My original version of this post forgot this important point. Now I understand why SteppIR went to such trouble to produce a very large switch with large separation between the “contacts” to handle the high voltages present. The cuts in the PCB material between each switch contact point reinforce this point.

The list of the issues with the 80 meter coil option include:

• Home-Brewish Inductor Tap Switch – The flimsy nature of this system still begs for a better approach, but I have to admit I cannot think a better approach in this price class
• Stiff wires on the moving switch contacts produce stress – high strand count wire may make better sense
• Weather exposed terminal connections for the stepper motor wiring – a good connector approach would be an option I would gladly pay extra for
• PCB trace-widths may not handle full power at the the 1,500 watt rating especially with the higher currents feeding the lower impedance of a short monopole. My calculations for 10 °C rise for the currents expected into, say, a 25 O antenna start at 0.1 inch with 2 oz. copper thickness. The PCB board has ample room for wider trace widths.
• Power off default potentially undefined

Soon I will post some details of suggested improvements to take SteppIR’s brilliant thinking into a better engineered approach.

A purchase of the BigIR vertical is a certainty for me. The enormous 80 meter option is a reasonable value at under $400 and would be a for-sure purchase if it wasn’t so large and I had not seen the inside home-brew switch. Still, the high voltage tolerance of SteppIR’s unique rotating PCB switch is, perhaps, a clever affordable solution that brings a good solution at a good price point… nothing wrong with that.

In SteppIR Antennas’ defense, product development can be quite a pain, especially when targeting products for notoriously stingy hams. The fact they have products for us to buy with their unique twist is a good thing for amateur radio.

To highlight their cleverness this is a best guess schematic of the RF paths…

The RF Paths in the SteppIR BigIR 80 m Option Coil

The most interesting portion of this schematic is the wiring of the coax wrapped toroid. It is another clever SteppIR design feature that helps match 50 ohm coax with the ~ 14 ohm impedance of a series inductance base loaded monopole antenna.

You are doing a good job SteppIR Antennas. With a few tweaks you will have a near perfect product. On the other hand, for the price you just might already have a near perfect product.

SteppIR, please take note… I would be delighted to pay another $100 for a good weather proof connector for the motor signals.