We depart from our usual hand tools and hands-on power tool enjoyment this weekend to begin work on a seminal project: The ultimate ham radio wire antenna system.
Long-term readers of this site will remember that we’ve already done one spin on an improved HF antenna. Called Super Antenna iV it offered better performance than a simple dipole (two, back to back 1/4 wavelength wires, fed in the middle comprising an) antenna.
What that antenna has proven on the air (and I’m a harsh critic) is that even with the smallest of my ham radios (like the uBitx 6.2 which is available for just over $200 out of India), I can work around the country quite well on just 10-15 watts PEP (peak enveloped power if you’re not yet a ham). Depending on band conditions, of course!
Therein lies an interesting story (at least to ham radio addicts) so let’s begin with the antenna modeling results table and the newest antenna which is named Evolution 3. Dipoles and Off-center fed variants were 1 evolution, while 2 was the thinking that led to Super Antenna iV. Evolution 3 is something old plus something new… as we’re about to unfold.
It’s All About Performance
Welcome to UrbanSurvival Extreme Antenna School!
So let’s line up the first set of data and you’ll see why as common (and cheap) as a dipole is, there’s as much as 7 dB of “free gain” to be had by getting clever in your antenna designs.
Introduction to Decibels
In order to comprehend the difference between a dipole antenna at 3.6 MHz (low end of 80 meter ham band, digital and Morse territory) we need to spool up a quick intro to decibels (a bunch of 10 log math) which is made ever so-much easier by just using an online calculator like this one.
On 40 and 80 meters the Evolution 3 more than doubles effective transmit power over a simple dipole. On 20-meters? Five times the effective power.
Let me back up and take this step-wise because these are huge claims:
Start with a Dipole
Our first antenna to consider is a simple dipole with 68-feet of wire, either side of the center, and fed in the middle. It works; and pretty damn well, too. Considering it’s about the cheapest cost for most dB of signal of ’em all. Here’s how it performs.
As you can see, it has some gain – about 4.85 dB. over an isotropic radiator. In free space it would be a “dog bone or toroid shape” antenna pattern. Up, close to the ground (even 50 feet up) it still radiates most of its signal (*more or less) straight up on low bands. This is great for NVIS – near vertical incident skywave. Think 80-meter (3.5 MHz) use.
Now, let’s review the Super Antenna iV and how it worked on the same frequency: (This is a SAiV plot…)
As you can see (both by comparing the table data and the charts themselves, the Super Antenna iV on transmit was 2.29 dB stronger than a dipole.
When we put this into the calculator, that’s like increasing transmitter power from 10 watts (on a low power (QRP) radio up to a hair under 17 watts.
How did George get 70% more effective radiated power? The secret is in the wires. Laid out in the EZ-NEC antenna modeler like so:
As an experienced ham would spot, this is basically an OCFD (off-center fed dipole).
But, the “secret sauce” I found for this build was the addition of more wires on the long side of the antenna. At the center, these all tie in to the feed point. But, at the far end, they are spaced out 3-inches apart. Importantly, they are NOT connected at the far end.
This latest antenna “breakthrough” being unveiled here (as the AC7X Evolution-3) completely kicks-ass of both the above antennas on the three most used ham bands by me; 80, 40, and 20 meters.
Here’s how the 80-meter antenna gain calculates and I think you will agree, it’s impressive!
To give you the same sense of what the payoff is in terms of power? The EVO-3 (first was dipoles, second was optimized OCFDs and this is…well, you’re following, right?) sports 4.68 dB of power gain over a Dipole. Which means that example 10-watt transmitter on a dipole will “get out” like it’s output power is 29.4 watts.
20-Meters Blew Me Away
As impressive as the 80 and 40-meter performance was, I couldn’t help but get excited when I ran out the 20-meter performance. It was mind-blowing!
Here’s the “side view” (Elevation) perspective: Initial Evo-3 on 20:
WHAT??? Yes, 12.43 dB of gain!
Now let’s compare how it works on 20-meters with a 10-watt transmitter: 5.18 times (7.14 dB) of gain over a dipole means your signal will “get out” like you were running 51.8 watts. Or, if you’re someone like me who uses 1.2 kw on CW- Morse, this means it’s like keying up 6,216 watts!
Even better? The pattern (view here is top down) squirts out in four major lobes down at a TOA (take-off angle) of 20-degrees:
This also means that when installed in the East-West position, the major lobes will be toward Europe and the Western Pacific and will be heading toward the Caribbean and South America, nicely.
What’s the Secret Sauce?
This antenna uses a very different wire plan than the simple 4-wire array at the heart of Super Antenna iV. More wires, too. As you can see, it’s both longer and there are two “parasitic radiators” I’ve installed that help the SWR look so good.
Please note, if you do opt to experiment like this that Wire #2 is a #10 gauge wire. Because there are five 133-foot runs of #14 out to the antenna support on the far end. #10 is needed to handle the weight.
The parasitic resonators help to tame the SWR a bit.
SWR and Reflected Power
When fed with open wire line (where transmission power losses are minimal (typically 5% or less) the SWR is not “critical.” Open wire losses are minimal, even with high SWR. Even so, the antenna’s performance on 20 meters might justify construction. Look at this SWR curve:
A return loss of 17 db worst case (bigger numbers better) and a 1.33 SWR across all of 20 meters is unheard of. 12.43 dB of gain is what you’d expect from a beam antenna and a tower costing thousands. This is wire. And this is more than 14 dBi. (12.43 +2.15 db)
Even so, feeding this antenna does require the use of open wire or ladder line feed systems. This means an antenna tuner. One large enough to handle about twice the transmitter power you plan to use.
The best antenna tuner I can think of is the old Johnson Matchbox series. These were solidly built and did not have issues like toroid saturation and heating and other such finery.
They work great. One reason? Even the smaller (low power) version of the Matchbox would handle 275 watts of power. But, when you multiplied that times four – to account for 100 percent modulation on AM which was commonly used in the “old days” it meant the matching unit could handle 1,100-watts PEP. So even modest powered amplifiers (like the Heathkit SB-200 or the single 3-500Z or 3-400 series amps (like my Loudenboomer HT-45 would work fine.
Working with the Discoveries
There are two new ideas in this antenna. The first – which became apparent from the design of Super Antenna iV – which had a total of 3-wires (each 90-feet long) on the “big” side of what is an idealized OCFD (off-center fed dipole) – is that the more wire on the “long side” the better, in terms of gain, and such.
When you add additional wire on the long side of an OCFD remake, the nominal impedance can go all over the place.
This is where the addition of non-connected, semi-parasitic “impedance tuning” stubs comes into play.
There’s a further set of wire configurations (closer to what I will build) where the parasitic stubs are moved 6-inches toward the long end and are NOT connected to the feed point.
This results in the following data improvements:
SWR across 20 meters with a single set impedance (196 ohms) looks like so:
Realizing this result will be very close to a 4:1 balun. Or, in my case, using 450-ohm ladder line and a balanced tuner (old full KW Johnson Matchbox).
And across 40 meters:
As should be clear, this is about perfect for a 600 ohm open wire feed.
Summing Up This Iteration
Here’s the performance I’m aiming for when the weather cools off:
Remember, the gain figures are isotropic minus 2.15 dB. Which means that where 13.2 dB is shown in column 6 of data, the isotropic gain is 15.35 dBi. The 7th column (DBD) is the Evo-3 gain over dipole while DBSA is Evo-3 gain over Super Antenna iV.
There’s actually a good opportunity for antenna modelers to “push around tuning” with additional parasitic tuning stubs on either (or both) sides. Just remember that you will begin to get “model contains losses” errors. This is because the more wire (and magic) the more losses can accrue.
Where does all this gain come from? Glad you asked.
Depending on height above ground, the typical dipole (or OCFD) has something of a “top hat” look to the elevation view. A lot of energy goes out at a low take-off angle (good) but there’s still a very sizeable vertical component remaining (the top hat – bad, except when using NVIS on 80).
What I’ve done in both of these designs is “push wire around” to take (on 40 and 2o meters) this “wasted signal” and squish or coerce it down into the more useful take-off angles.
This iteration maintains a flat SWR (under 1.5:1) across all of 20-meters and all of 40 meters. A good (preferably open-wire or ladder line) feed is needed on 80 meters:
When modeling this antenna – so as not to be led astray by local conditions – consider updating the default ground conductivity in EZ-NEC to values shown in the FCC guidance here. Useful for those of us who can’t afford a salt-water waterfront home with no CC&R’s!
Those will have to wait for a future edition of ShopTalk Sunday. I’m still very much pleased with the original Super Antenna iV design. And I have to pick up another cheap plastic cutting board at the Dollar Store. (For some reason, we’re not too thrilled with going out in public, lately, even with a masks on…).
I have a couple of options with the antenna insulators, but the “double belt” type ham-made center insulator has great mechanical properties.
Launching this antenna will involve the new .22 caliber “dog training” muff, repurposed, as Bob Heil outlines in this video.
Also need to get another 500-foot spool (or two) of #14 stranded and a good piece of #10, as well.
Doesn’t bother me taking a “weather delay.” Too hot here in Texas for another month or two, anyway. But that’s time when I can answer questions and see what other ideas and models people might want to share.
Then Elaine Showed Up
There is a “super-tuned” Evolution-3 that can model as high as 20 dB. of gain in a cloverleaf pattern at a 20-degree takeoff angle across all of the 20 meter band.
But when I asked Elaine (KG4YHV) to hold a measuring tape at the tower while I walked out 140 feet, the hammer came down. “I don’t want you cutting down that (longshore language insert deleted) pine tree!” (She seemed pretty serious. Sigh…Did Benjamin Franklin’s wife hide the kite string?)
Since every problem is an opportunity with it’s clothes on, I went back to the modeling. Eventually something called Evolution 4 (Evo-4) evolved.
The Wire Table looks like this:
And here’s how it stacks up performance-wise.
This build also promises decent performance with a fair cloverleaf on 20, 90 degree NVIS takeoff on 80 and 40 degree takeoff angle on (what else?) 40 meters. 80 through 20 meters in order:
These SWR values are all quite acceptable (better than most commercial crap out there) on all three of my bands of interest: I may do additional modeling to bring down the upper reaches of 40-meters, but that’s not a major priority.
Construction Quality Matters!
This is NOT an antenna that (unlike a dipole) is “close enough and works great” even if the two halves are an inch or three different. Those antennas work great regardless and can be easily fed with simple coax.
The Evolution series is different. It’s a kind of “grown-ups” antenna. Because it’s final performance will be dependent on the skill and craftsmanship of the maker.
Some markers along the way? You bet.
As a general construction concept, you’ll need to design a center insulator that will hold up to the much larger than “usual” antenna loads. This doesn’t just mean a bigger center insulator: Think of your halyards, working load wind strain relief, and even things like ice loading if you’re up north. Remember, use open wire or ladder line!
Second point is there is a huge GAIN and Q trade-off in the spacing of the parasitic *SWR/impedance) elements. Wires 6 and 7 in the Evo-4 and wires 7 and 8 in the larger Evo-3.
To show you what I mean, look how far simply spacing the parasitic elements at 6 inches off the radiators looks: very tame and 11.3 db. of gain on 20. But move the parasitics in to 0.15 foot ( 1.8 inches spacing) and now you can push 20-meter gain up to 14.66 dBref (isotropic minus 2.15 db) , but the shape of the 40-meter SWR deteriorates faster at the high-end of the band.
I’m a CW op, so who cares? Data, sometimes, so good there, too.
There is no free gain, though. Voltages – especially if you run a “gallon plus” (more than 1,000 watts output) will be up in Tesla land. Coronas are not welcome here, (see the beer exception clause!) so a bottle of corona dope on all connections at the feed point are in order!
Anyone can be a ham. With enough tinkering and study, anyone can have an Extra Class ticket – top shelf qualification. (I’m proof! AC7X, So’s George II, KF7OCD) But around here what shows your stripes is knowing when to break out the MG Chemicals – Super Corona Dope, 55 ml Liquid Bottle. If you have to ask? Put up an end-fed half-wave and go have a beer. One of those (OK) Coronas.
Gain Tweaks and Construction
Final construction point: The amount of overlap of the parasitics is a critical dimension. A suggested value show (0.3 foot, or 3.6 inches) is derived from many data runs. This is precisely why your personal build quality will come into play putting this kind of antenna together. Remember the parasitics overlap the center feed point by less than 6-inches and this is a somewhat critical dimension. Gain goes bye-bye if you don’t build to the model.
One version of the Evo-3 full-sized reported over 21 dBref (about 23.5dBi) of gain across the 20-meter band. Think about the implications of this: 1,200 watts of key-down CW (code) output into more than 16-dB of gain over a dipole, that is almost like sending an invitation out for an FCC field visit.
So crazy are these kind of gain figures (not built, but evolving on paper in modelspace) that a “surprise visit” from the Feds might become a real possibility. What an ad for a new antenna, huh? Particularly difficult would be explaining how a ham station can be keying the equivalent (in one run) of a 32.8 kilowatt shortwave transmitter while remaining inside the FCC’s new and evolving tighter standards for human exposure to higher RF power levels. (I’m working on it – remember, we have 29-acres to play with!)
Like I said, SuperAntenna iV is simple enough and gets out just damn well now. So what if it’s only 4.11 dB better than a dipole on 20 already? See how simple SAiV is?
My plan is to build the Evo-4 antenna. Sometime this fall get it on the air and try it out. But the FCC’s exposure limits are real and my office (and the house) are near field at 65 and 80 feet from the center feed point. Even if it works perfectly, the world is changing.
We may have to stop optimizing of designs – and “fix them to conform with regulations” first. Or all relearn CW (the code) because we can double the power and average, lol.
Sort of like what’s going on in politics, gender, race, finance and all the rest. Except quadrupling there…
Hand me the kite string, again, would you?
Write when you get rich,