Ham Radio Super Antenna – Plans, Build, Results

A Convenience Store Based Antenna

Ham radio operators world-wide would love an antenna that is cheap, easily built out of locally available parts – and outperforms both standard dipole antennas and other commonly-built wires.  Well, here it is….

After almost a year of modeling our ideas for a “Super Antenna” the design was locked.  It was built and put on the air during the CQ Worldwide contest last week.

It was a pile-up buster. (To non hams:  it kicked-ass!)

In a space of 1/2-hour, I logged Portugal, Aruba, Italy, and somewhere in ITU Zone 29 (roughly Azerbaijan.  Plus, uncountable contacts state-side.  And when these basic signal contacts were done, had a nice +30dB over S-9 on C.W. (amp on, NY area from Texas).

All on an antenna you can make for about $65-bucks and a few hours work.

The “Secret Sauce”

Every antenna builder/designer claims they have some “secret sauce.”  I’m  no different.  EXCEPT that I have run my “secret sauce” through countless iterations modeling.  

Setting up modeling software is important for proper evaluation.  In EZ-NEC (pro), careful attention was paid to setting up both the ground conditions (Real- High Accuracy) as well as the reference antenna (2.15 dBi) which enables dBd (decibels relative to a free-space (isotropic) dipole.

>>>> The “secret sauce” after all these iterations?  Antennas work best when there are multiple conductors on  one side of a center feedpoint.  Usually, a couple of dB!

At the center, all these additional wires are connected together.  At the far end of the antenna, they’re 3 to 6-inches apart but NOT tied together.  The effect disappears if you do that…

Walk-through of the Secret

With a simplest dipole (like for 20 meters), you have two pieces of wire, each ~16.7 feet long.  These are hung in the modeling software  (as a flat-top) at 50-feet.  Signal source  is attached:  Center conductor to one side, braid or opposite side of ladder line to the other.

And it will work.  Very well, though it depends on aim.  You see, the traditional dipole  antenna fires broadside (perpendicular) to the antenna.  Since it has significant lobes when plotted, the antenna has up to 5.36 dBd in broadside directions, but will perform poorly 90-degrees to those lobes.  The 5.36 db is “pulled in” from the end lobes.

The Dipole is not perfect, though.  Significant energy is “wasted” going “straight up.”   The effect (top hat pattern) is more or less pronounced depending on elevation above ground.  Fine on 40 and 80 meters, where NIVIS (near vertical incident skywave) is desirable.  But not on 20 where the best take-off angles are low to the horizon for long distance coverage.

The area in yellow, here, shows the “wasted” signal from a dipole that doesn’t help with long distance communications.  Great stateside, but in Europe of Africa?  Not so much.

Now, let’s take the exact same antenna elevation and tweak.  We’re going to  add a couple of wires on one side. All wires tied at the center, 3-inches apart at the ends (and not connected out there).

See what happens?  Our performance for long distance work improves!  A LOT! 1.48 dB.  Effectively we pull from the (marginally useful top hat area and redirect it down toward the horizon.

What my crude drawing shows (Blue arrows) is that energy has been taken from the vertical lobe and has been redirected down to the more useful (for long distances) 20-degree take-off angle.

See?  We pick up almost 1 1/2 dBd  Adding two additional 16.7 foot pieces of wire.

Now let’s get to work optimizing!  Spoiler alert!  Using a single 49 foot run on the “hot” side and three 90-foot wires on the other this antenna begins to rock…

OCFD & Windom’s Work Better

Since the “secret sauce” is additional wires on the “cold side” the “regular dipole” becomes even  more unbalanced.  We can then exploit in the following design:

Which results in a marvelous signal on 20 meters!  (And OK on 40, plus very good on 80…too!):

As should be evident, with the Off-Center-Fed Dipole (OCFD) (also called a Windom, by some, though a Windom uses a single -wire feed) we have “squished” the vertical lobe down and increased the low take-off energy…dramatically.  In fact, here’s a performance comparison in table form:

This is based on the hot side wire being 49-feet long and the three cold side wires being 90-feet long.  Different elevations will yield differences, but the AC7X Super Antenna wins every time.

I call this the 49-3X-90 design.  49 feet on one side, three times 90 feet on the other.  It’s a convenient way to keep track of dozens of designs when optimizing.  Just use a standard elevation and ground.

You Need Open Wire Feedline

Ladder line is fine, too:  300 or 450 ohms, your choice. 300 MIGHT be better, but barely measurable.  Ladder line has much lower loss at high standing wave ratios than coax.

Before you run out and build one, realize this is the ONE fly in the ointment: while it will work dandy on 3.5 and 14 MHz band with a 2:1 balun, you will need an antenna tuner  and open wire feedline to nail 40.  This is because on 40 meters, the antenna impedance is around 273 ohms.

On 20 meters, a 2:1 balun will give under 2-to-1 SWR across the whole band. But not get better than 3 1/2 to  on 40 without “help” which is why the ladder line tuner.

On the other hand, as a high-performance (and good gain) antenna on the 20-meter band, the antenna is hard to beat.  Better than my beam (*which has a broken trap) by far!  From the bottom of 20 (1.85 : 1) though the top (1.54 : 1), the SWR is flat at 14.2 MHz.  You can’t beat them numbers with a stick!

Convenience Store Insulators

The first version I put up employed a commercial ladder line center insulator.  Broke in the first good wind.  Use of 20 percent infill in innards of  the plastic molding was the cause of failure identified.

This means you will want to use something more solid.  A super-tough plastic like Delrin is great.  But, have you priced that stuff?  Wow!

A trip to the local convenience store paid off, though.  A super-tough piece of antenna insulator, one-half inch thick, is widely available.  Although people buy them mistaking them for 1/2″ to 3/4″ thick  “cutting boards” not as antenna insulator raw stock.  Go figure.  World’s full of heathens, though, ain’t it?

Off to the shop, where we rip off the rounded edges…

Which led to Learning #2:  Table saws leave ugly melted plastic sticking to the edges:

You can peel most of this off by hand easily enough.  Some touch-up on the belt sander brings it back to useable.

For following  cuts, I was bright-enough to use the band saw.  You will want to lay out your “cutting board insulator” something like this:

Yeah – I know.  Not a “standard looking” insulator.  But, here’s another “crackpot theory” for you: 

On most antenna insulators, people twist wires “back on themselves.”  I know “the books” say this doesn’t matter, but instead of “back on themselves” I chose to set up a “belt” approach for all wires.

The wires go in the outer hole, around the back, and out the next one.  This way, there is no “conductor reversal.”

Same thing with the ladder line:  Goes through the three belt-like openings which were cut on the milling machine.

Just before assembly, the insulators looked like this:

At the center insulator, everything ties together at the two bolts.  They go immediately to holes about 5/8ths inch apart.  On the “special side” of the antenna, there are spacers every 20-feet, or so to keep things from twisting up too much.  It wants to without them.

To keep the spreaders in place, I put a large drop of 5-minute epoxy at each spreader-wire joint on the top wire ONLY.  I’ve tried small zip-ties, but they slide.  These will over time – if you show up with a D-6 Cat to pull ’em…

The wire used is el cheapo electrical supply house (or eBay overstock 500′ rolls are cheap) #14 stranded THHN.   Sautéed lightly in rosin flux and then tossed into a telegraph splice if needed.  On the ends, sautéed wires are crimped into ring terminals that land on stainless bolts.  After being properly dressed with solder flowed into each.  (Can you guess who was hungry when writing?)

So there you have it:  The AC7X Secret Sauce Antenna – the 49-3X-90 – and how to build one on the  cheap.

When I get some time in TinkerCAD, I will draw up something more elegant – designed for printing in ABS – and will put it up as an .STL file both here and over on our https://ultra-make.com 3D printing site.

That design will likely have additional “belt loops” and I’ll try to fit it all in the 220 mm X 220 mm footprint of the  Ender 3 type printers.   Not everyone has a CR-10 MAX yet.  But you do believe in  Printer Claus, right?  Make sure Printer Claus lands on your tower before the next lock down and brings?  Filament and antenna wire, Rudolph?

Oh…and Dummy loads for people in W-6 and W-2  land.

Write when you get rich (or make DXCC),

George@Ure.net  (AC7X)

31 thoughts on “Ham Radio Super Antenna – Plans, Build, Results”

  1. George

    ” Although people buy them mistaking them for 1/2? to 3/4? thick “cutting boards” ”

    Now you’ve done it! You went and gave away the Great Secret we tinkerers have been hiding for years. Now the price on plastic cutting boards will go sky high!

    “Delrin is great. But, have you priced that stuff? Wow!”

    Delrin is widely used in the automation world especially in machines in the pharmaceutical production area. It’s properties make it a good replacement for metal in certain applications.

  2. Mr Ure,

    Can U send Bitcoin over that there new fangled antenna ?

    Dude, we just had the All Time High Monthly Close in Bitcoinz – October,2020!

    Why U and BTC can fly..https://youtu.be/HfxqQmWtGNM

    Can U catch a Cold/Covert19/Flu from Ham Radio use ?

    R U sure ? You should be very concerned about catching the deadly” covefefe” virus from Ure Hams.

    The good news – all the Living in FEAR mask Wearers – have sooo much to look forward too in the coming years ..

    Hello – Post Traumatic Stress Syndrome.. Thanks 4 Ure contributions to the Global mind F—, G!

    – PTSD if diagnosed “properly” will score U a Sticky-Budz License/Card –

    -“Killing em slowly – longer it takes, moar money we makes..” -“mr globalist”

    Happy Anniversary ! https://bitcoin.org/bitcoin.pdf – Brilliant & Super Clean !

    If U have never read this – well…

    NO Bitcoin 4 G !

    • Ure’s investment in gardening gear may outperform ur btc’s. 2022 I figure. Still on with 3,000 s&p by year end.

      How many calories in one of them?

      And tell me how they work with grids hard down?

      • Isn’t December 31, 2020 the long anticipated Mcafee D-day ? Will LCN and the other crypto-fiends act in solidarity? Will all those crypto enthusiasts be forced to wear hospital masks in 2021? Stay tuned, G____.

      • Thats why Elon’s throwing Starlink up into LEO. Of course grid down makes for an unpleasant surprise when all those purveyors of trinkets that you’d want to exchange for your hash codes for aren’t as prepped as the readers here.. Of course when the reset IS triggered I’d expect grid down as SOP to freeze everyone’s finances in place until a certified treasury representative can inspect your crypto, remove it, and replace it with CBDC at the “fair value” price fix prior to said grid down. Restart the grid, and watch the new purchasing power equivalency of select crypto currencies skyrocket against CBDC. Think it can’t happen here? Study gold and 1933. The only risk that has changed is that the store of value is digital,in the cloud[which has its advantages in regard to portability and security]. Not precious metal [though you should have some of that too]. Not your keys not your crypto. Keep your crypto off the exchanges. caveat emptor and good luck.

    • Bitcoin is the gold coin of this new Digital Age. Just needs to be more widely accepted & will so become over time. Remember when bitcoin was $20,000 & some car dealers were stumbling over themselves selling cars & trucks using bitcoin as a currency. As usual with something new, scams, & after a while, bitcoin will clean up its act to be an acceptable & reliable method of exchange like the US Dollar. Right now it is the wild west with tremendous upside potential.

  3. Well George, the self proclaimed tool slut, showing off his combination square set, I have never needed all 3 heads on at the same time, but nice, showing your stuff, I would rather, you would have a photo of the mill set up, ya , I be a little tool slut. The cutting board is most likely a HDPE product, by the way it melted with the table saw. Still good for your use. Here is a link to a short conversation, how does it smell? does it float? https://www.polytechforum.com/robotics/how-to-tell-if-cutting-board-is-delrin-17510-.htm
    you know the old saying,,”does it pass the smell test”,,”something just doesn’t smell right” seems to apply to more than just politics. sour milk smell?
    Have a good day George.

  4. I love it when you talk ham radio, George. You should write these instructions up and publish it in QST. Thank you!

    • I submitted a version of this to them a week back – will be a couple of months for their editorial process to thumbs up or thumbs down. Such a simple improvement on an ocfd I would have thought someone would have already come up with it…

  5. Yesterday, in the late afternoon, the local families held a costume parade for all the littles that passed near my house. It was encouraging to see so many young families and kids out enjoying the occasion and each other. Felt like another time.

    As they passed we noticed people were looking straight up. A spectator stopped by, a bald eagle! It slowly circled and watched then drifted off, looking for whatever it was looking for in the middle of town. There are a few around, but I’ve never seen any this far from the river.

    A striking animal spirit saying (to me) this is freedom, this is America, hold faith. The whole scene was suddenly much more beautiful.

  6. Here I am running a 40m OCF dipole. Using a Balun Designs 4:1 with a 1:1 choke built in. Some good wireman wire.

    I am QTH challenged.

    Nothing fancy but It gets out.

    Details on QRZ.

    KX4WQ

  7. The only improvement I plan to make on your design is the insulator/spacers on the wire. I plan to use short sections of 1/2″ PEX tubing. Lighter in weight, and I plan to use a few more of them more closely spaced. Now if the big box hardware store would just get my drill press back in stock so I could finish drilling them!

    My ‘closet workbench’ is coming along nicely. I installed a 2’x4′ piece of pegboard on the inside sliding door for hanging larger tools that don’t fit well on the small shelves and drawers above the bench. Will have to send you better pix when I get it all fully populated. Since I don’t have ‘Texas-sized’ space to work with, It’s a full electronics workbench in a closet in my spare bedroom/ham radio shack. This keeps me from doing electronic projects on the ham radio operating desk.

    Your next business opportunity: Mass produce your antenna for sale to the tool-less appliance operators!

  8. Contractor’s note: Reverse the blade on the tablesaw, next time, so it’s running backward. This is how plastic siding, soffit, flashing, etc, and PVC plumbing are done on a table or chop saw, because it cuts clean. I’ve never stopped to figure out why, I just know they all do it that way…

  9. Not to bring up the laptop from hunter biden but Alex Jones has a pretty good show today..
    The next thing we will hear is how the president pretended to be hunter biden and did his voice interpretation of hunter biden and all the national secrets on that tablet hard drive along with the documents were planted there..

    GMAFB…
    Of course the alphabets will do the hokus pokus and it will all vsnish

    https://www.infowars.com/posts/sunday-live-hunter-bidens-laptop-revealed-to-contain-classified-information-experts-says-major-national-security-risk/

  10. Lol lol I just thought of a true horror story…
    Election day… all the seats up for grabs turns Democrats with the house and the Senate flipped..
    When that happened with the Republican party they still didn’t do anything . I think the reason was.. what if they did something and it was the wrong thing.. would the Democrats do the same thing?

    Just listened to Biden speech and ges going to make sure medogathca a fundamental right

  11. George, a question about the antenna. Are the three wires oriented (my best guess) one above the other in the vertical plane relative to the ground or (less likely) side by side in the horizontal plane relative to the ground?

    Thank you for the rest of the details on the design.

  12. I am also curious as to the ORIENTATION of the wires once the antenna is up.

    Are the longer wires HORIZONTAL to the “hot” wire, or VERTICAL to the “hot” wire? If vertical are they ABOVE or BELOW the “hot” wire?

    For years I ran a multiband dipole (40 /20/15) with the wires spaced about 2 1/2 to 3 inches from each other the length of the dipole. The wire for each band was cut for THAT band and all were fed via a single feedline into a common center balum that all the wires were attached to (4:1 as I recall). The antenna worked reasonably well (is available to buy commercially, but you can make your own for about 1/4 the cost), but the wires were in a vertical plane to each other. I never though about trying to get them into a horizontal plane to each other (not even sure how I would do that, so just thinking theoretically here).

    Anyway … any info you can give as to the horizontal vs vertical orientation of the wires towards each other would be appreciated.

    • refer to the wire table included in the article
      49 feet hot side, 90 feet cold side (tied at center feed point, 3″ apart at ends) All in a row, however gain is also evident in inverted vee installation, I just didn’t “apex angle”
      because that would be too big a table and would constitute something verging on ‘werk’
      73

  13. When you refer to the “cold” wire, are you referring to the braided shielding wire of the coax? If so, is the “hot” wire the center conductor of the coax?

    • Antennas always have a “hot” and cold side to them. The cold side is the one at ground (dc) potential. So, in this case, the 49′ leg is “hot” and the 90 (3x) wires are “cold.”
      Something most hams don’t realize is that when you get RF ‘bites’ off a metal mic, that is because the system is operating “upside down” – that is, the cold (normal ground) is radiating, not the desired element. We ran into this a lot years back when I headed up sales for the Bellevue Wa SSB emporium. People could call in and say “My SmarTuner won’t find a match” or “I get r.f. burns on my radio…” Invariably, insufficient grounding is THE reason. A tuner may (or may not) find a solution when a ground is being loaded. But if you have 50 feet on a back stay, a couple of very low impedance grounds to salt water, and enough foil laid down on the hull to form a gigantic coupling capacitor to sea water, then the little antenna on the back stay will get out like gang busters.
      On the other hand, if the ground is insufficient, the “hot” end (always the electrically smaller element) will radiate and that’s a bad thing.
      Unless you are doing radio tomography and looking for subterranean tunnels, but that goes off into classified weeds along with the drop-in spread spectrum jamming buoys…

  14. PLEASE DO NOT POST MY NAME or Calls THANKS

    Hello- I see the posting on the super antenna. You mention cutting board materials. If memory serves me correctly this is a form of Polyethalene (spelling)
    We use a form of this in the potato processing industry as do most raw food processing factories. Its called UHMW. Its a material that can be procured in sheets and sticks, in colors etc. It can be machined, cut with a table saw or milling machine etc. It is ideal since it has a surface that is tight like stainless steel and can be cleaned to food grade standards. Its not cheap but reasonable per other alternatives. One issue that it presents is that it does NOT like sunlight. Over time it will crack and shrink and decay. I was warned of this when I got permission to obtain some surplus pieces of it. I would suggest that it be painted with a good quality outdoor paint. If it will stick to the surface- it should make the stock last longer. Hope this helps. Wish you lived closer, as I would be happy to share my surplus UHMW with you. Russell

Comments are closed.