With the proliferation of Yagi design programs like AO, YO, EZNEC, Yagi Mechanical, etc. everybody who has a computer has the ability to design a well performing Yagi antenna.

Many of us have spent hours before the computer screen tuning and changing things until we have the perfect antenna for our purposes. Then we turn off the computer and start looking at antenna catalogs to find one that might come close to what we want and can afford.

Yes, there is a difference between designing an antenna on a rainy Saturday afternoon and actually getting it built and working. But it may not be as big a difference as you think.

Let’s analyze the situation.

Most of us don’t have an unlimited budget for antennas. Plus, there is the basic fear of “What if I go through all of this and the antenna doesn’t work?” I’ll be left with a useless pile of aluminum, become the butt of jokes from my Ham friends and stand accused of squandering finances by my spouse.

We’ve all been there! And no one wants to go there again!

On the other hand, most, if not all of us can point with pride at something that we have built from scratch that turned out so well that we show it to everyone that shows up at the door.

So, think about it. What were the major differences between the things that turned out to be a source of pride, versus some other project that ultimately was hauled away by the junk man?

For me, the major differences were and are:

1. I had fully analyzed the problem so I knew what I needed to accomplish. I didn’t decide as I went along.
2. I knew my Time Budget: I had arranged things with the family.
3. I knew my Money Budget and the project fit into it.
4. I knew what I was doing or I had excellent instructions either from a trusted book or from a friend. Maybe I even had the friend there.
5. I had the correct parts ahead of time – I didn’t try to substitute or cobble something. Saving $5.00 and gaining a problem or an eyesore just isn’t a good tradeoff.
6. I had the correct tools.

The second question might be a little harder. Keep in mind that most antennas designed for the Amateur community seem to be rated for about 75 mph. There are exceptions and some are even rated at over 100 mph. The point being that you could design for a 75 mph wind survivability and be neck and neck with a lot of the ones that you might otherwise buy. In fact, one of the ham magazines sells it’s own brand of antennas and according to a graph on their website, they will withstand only about 50mph. That could possibly be a little low for some locations. Check with your local airport for wind speeds in your area.

Software Design Tools

OK – how do you figure out how to design an antenna for a certain wind speed? Well, you could go to engineering school and study the theory of cantilevered beams or you could just go to the DX Engineering website and purchase a copy of Yagi Mechanical, which will allow you to design the antenna elements to resonate at a specific frequency and to withstand the wind speed that you specify.

The part that attaches the element to the boom is, quite naturally, called the Boom-to-Element Bracket. Keep in mind what size element the Boom-to-Element Bracket will accept since that will be the largest size that you will want to specify in your element design. Also, keep in mind what is the smallest size aluminum that is available since that will be the smallest diameter that you will want to specify. Typically, the most economical way to design the element is to use single thickness tubing (.058 wall) for all of the sections. Later, if you can’t make it long enough without exceeding the specs of the aluminum (35,000 psi for 6063 aluminum or 40,000 for 6061 aluminum), then increase the thickness of the largest section you can use and try again.

If you slide an additional piece of .058 wall tubing inside the largest section you will be able to make it longer without exceeding the yield strength of the metal at your specified wind speed. Thanks to Yagi Mechanical, you won’t have to actually do this with metal – you can try out whatever configuration suits your fancy right on the site and it won’t cost you a thing.

When you finish you will have the element dimensions and taper schedule that you can take directly to your Yagi Design Program, hereafter to be called your YDP.

Yagi Mechanical will have also provided you with the correct overlap of the individual sections of the element.

You can also use Yagi Mechanical to determine the diameter and thickness of the boom that you can use given your boom length and wind speed. Just treat the boom like an element and realize that the program looks at just one-half of the boom (or element) when it is doing its analysis.

Your YDP will adjust the last section of the element to get the total length of the element to be correct for the antenna that you are designing. Luckily, basic physical laws dictate that this section is the longest of all the pieces so it is available for adjustment.

However, the reflectors of most Yagis are about 4-5% longer than necessary to be resonant at the working frequency of the antenna. What this means is that when you are using Yagi Mechanical that the target frequency should be about 4-5% lower than the working frequency of the antenna. Then your YDP will shorten the end of all of the elements instead of shortening the director and lengthening the reflector, which could reduce the wind speed survivability of that longest element.

OK – Let’s design and build an antenna!

As you can see it comes in 2 pieces and clamps together with DXE stainless steel hardware. It insulates the element from the boom so that you don’t need to adjust the element length to compensate for a metal mounting bracket.

There is a very important distinction between building a beam with insulated brackets and the all-metal (sometimes called the Plumbers Delight) bracket method. The all-metal construction will almost always require that the element lengths be adjusted from that predicted by your YDP to compensate for the element widening and shortening effect that a metal mounting plate will have. If this is not done the antenna will probably still be a good antenna – just not on the frequency that you designed it for!

There are formulas for this (many formulas…) that attempt to determine just how much the length of the element needs to be changed. I am sure that at least some of them come close to being correct, but I would rather eliminate the need to modify the elements altogether.

For this reason, I have chosen to use the DXE Insulated Boom-to-Element Bracket, (DXE-BEB-2), which removes the need for any element length changes. The element is completely insulated from the boom. The antenna will perform well on the frequency for which it was designed.

The 6063-aluminum tubing can be purchased from Texas Towers; they run an ad in the back of QST each month. The 2-inch boom can be made from (2) 6-foot sections tied together with a 12-inch section of 1.875 inch tubing, which slides into each of the 6-foot sections and is held in place with 4 to 8 stainless steel sheet metal screws.

EM>Metal and Cable of Twinsburg, OH also advertises in QST and they sell 6061 tubing which since it is somewhat stronger will allow a lighter element. Their tubing is available down to .25-inch OD.

The boom to mast plate is a DX Engineering DXE-BMP-2, which is held to the boom with (2) DXE-SAD-200A stainless saddle clamps and held to the mast with similar clamps to fit whatever mast size you have in your tower.

The 2'' boom Hairpin Match, (DXE-HMS-1P) is a new item from DX Engineering and will match your 50-ohm coax to the approximately 25-ohm impedance of the driven element with minor adjustments.

The hairpin can be adjusted so that the low SWR point of the curve shown above will occur at any point in the 10m band, and since it’s a 3 element antenna, the driven element and the Hairpin will be close to the tower for easy adjustment if you change your mind.

Cutting the Tubing

Well, we have the lengths of the necessary tubing listed and diagramed above and we have a couple of sources. How do we get the tubing cut to the correct lengths and how do we mate it up? Good questions and this is where the additional tools come in.

There are many ways to cut the tubing. Some people just grab a hacksaw and put the tubing in a vise and hack away. STOP!!!! Those rough cuts at odd angles to the tubing are guaranteed to make your antenna look amateurish and second best.

The preferred way to cut aluminum tubing is to use a tubing cutter. Gee – what a concept!

The cuts will be smooth and straight and you can cut it to exactly the right length

Don’t use a cheap cutter. It will just skate over the top surface of the aluminum. You can buy a good tubing cutter at Home Depot for about $25.00. It’ll last for 20 years and if you’re the kind that builds antennas, you’ll never stop. Amortize it over the next 20 years and it comes to just over a $1.00 per year. Case closed.

The Tubing Connection

So What Did All This Cost?

Here's A Listing Of The Pieces That We Used.

Yes, you could probably find some 10m 3-element beams out there with similar prices. Let’s look at a couple of them compared to the one that we just “built”.

1 - Brand “” is the one that we just built.

• Boom length is 11 feet 10 inches
• Peak Observed Gain is about 7.0 dBd
• Front-to-back – about 25-27 db peak on a line that I use to indicate average value of an otherwise peaky aspect of most Yagis.
• Wind survival – 80 mph
• Price is $222.86 + shipping (See Note 1)

2 – Brand-Z is sold by one of the Ham radio magazines:

• Stated Boom length is 11 ft. 9-5/8 in.
• Stated Gain is approximately 6.3 dBd at the peak.
• Stated Front-to-back - 20 db
• Stated Wind survival – 50 mph
• Price is $256 + shipping (See Note 1)

3 – Brand-C is sold by everybody.

• Stated Boom length is 8 feet
• Stated Gain is 8dBd – (See Note 2)
• Stated F/B >20db
• Wind survival – None listed, but I entered the tubing sizes into the Element Design Tool and came up with about 95 mph.
• Price is $199 + shipping from AES (See Note 1)

Incidentally, both Brand-C and Brand-Z use a Gamma match that will make the antenna pattern non-symmetrical. The one that we built uses a balanced feed consisting of a Hairpin match.

Note 1 - Neither of them includes a balun, so for accurate comparisons I neglected the balun in the above table.

Note 2 - The Yagi is a predictable animal, especially a 3 element Yagi where tuning options are limited. There are only so many things that you can do with just 3 elements. It is always a tradeoff between Gain, F/B and SWR. As you saw in a graph at the beginning of this article, the boom length limits the maximum possible gain. The claimed gain by Brand C exceeds the theoretical maximum possible for the stated boom length according to the graph.

There is a famous book that Yagi builders (or buyers) should own. It is called Yagi Antenna Design written by Dr. James L. Lawson, W2PV (SK), and it is sold by the ARRL. I bought mine a long time ago and paid $15.00. It is worth many, many times that amount. In my opinion, it is THE definitive Yagi work. One of the graphs shows gain as a function of boom length and is the basis of some of my comments above.

Looking at the other 10m 3-element offerings out there I would say that you could build a much better antenna for a little less money than Brand-Z and for slightly more money than the Brand-C that has a boom that appears to have a boom that is too short for the claimed gain.

The wind speed survivability of the Brand Z is about 50 mph and of Brand C is about 95 mph. The beam that we built has a rating of 80 mph. The question you have to ask is: “How long has it been since my local wind speed has exceeded 80mph?” If it was not that long ago, then use Yagi Mechanical available for purchase and download on the DX Engineering website to design an antenna that will withstand whatever wind speeds normally occur at your location.

I am sure that there are many other ways to arrange the tubing to obtain the best wind speed per dollar of expenditure. This article shows a solution based on my criteria at the time that I wrote it. You are invited to purchase Yagi Mechanical on the DX Engineering site to discover your ideal element taper.