Building a 40-meter 4-ele monoband OWA Yagi on a 40-meter rotating tower
Pre-history
It started as a joke:
- A bit less than a year, I built my first-ever Yagi – a 10-meter 6-ele OWA monoband OWA on a 10-meter tower
- Then, I built a 20-meter 4-ele monoband OWA Yagi on a 20-meter tower
- The next antenna, for sure!, must be a 40-meter 4-ele monoband OWA Yagi on a 40-meter tower … 🙂
The remote QTH view before the star is born ...
2025.Feb.16
In the last few days:
- The first (bottom) mast section arrived to the site
- The rotating table and the first orbital bearings were brought as well
- Some additional materials – anchors for guys – were prepared as well
- Well after the sunset – literally in the darkness – we installed the version sections and enjoyed that it is rotating
- It is not guaranteed that everything will work, eventually, but so far so good, which is always encouraging
- Oh, yes, the rotator was shipped from China as well. It shall arrive in about two weeks in Almaty. I will hope to install the full tower to its full length by that time
The next steps:
- Assemble three more orbital bearings
- Assemble six more sections
- Bring everything to the site
- Finish the 40-meter Yagi
- Temporarily install the top section vertically and raise the 40-meter Yagi to it, and attach. Tune the elements to the band properly
- Design and assemble a 20-meter Yagi and install it below the 40-meter on the same top section as the 40-meter Yagi so that they will be raised on the top together
2025.Feb.11
The guys assembling the sections scared me even more. We discussed the design several times. I stressed that it should be a bent 10-mm wire (the design is from the previous tower). The confirmed they understand the task …
I shared photos of sections of the previous tower as an example …
Since I was all the time asking to share the progress to prevent any possible issues or a need for rework, the first thing I saw this morning was that they cut the wire instead of bending it as agreed…
2025.Feb.10
The last two days were very active:
- The rotating table and the first orbital bearing are done. It is unclear whether they are strong enough, where the metal can live long enough, where tolerances are small enough … Thus, a real test in the field with a smaller 6-12-meter tower is required 😉
The last two days were very active:
- The rotating table and the first orbital bearing are done. It is unclear whether they are strong enough, where the metal can live long enough, where tolerances are small enough … Thus, a real test in the field with a smaller 6-12-meter tower is required 😉
Current issues, uncertainties, and changes in the design on the fly:
- The orbital bearing and rotating table disks are wobbling too much. There is a high risk that they may jump from the side bearings completely. Potential solutions:
- Install the section on the rotating table and see the performance under the real weight. It shall pressure the metal of the table and minimize the wobbling. The same goes for the guys pressing the disks of the orbital bearing down. The real tests with 1-2 sections of the tower are required
- Use two bearings on the perimeters of the disk on top of each other instead of one – the resulting bearing will be thicker. Or find and install thicker bearings. Currently – 12mm (6301 bearing on the side for the rotating table and 6303 for the orbital bearing). This will reduce the chances of the disks jumping off the bearing completely under pressure, wind gusts
- Install the section on the rotating table and see the performance under the real weight. It shall pressure the metal and minimize the wobbling
- There was no metal with the proper dimension for some elements of the orbital bearing. Changes in dimensions for those elements lead to changes in the dimensions of other elements
- Too little margin was left in between the rotating table and protective elements on the perimeter. The protective elements’ height was changed
- The design of the side bearing for the orbital bearing was changed because the dimensions didn’t match somehow. The bearing was changed from 6301 to 6303
- It is not obvious that the rigidness of the plates for the orbital is sufficient. Maybe there must be a vertiсal ridge welded on top of the bearing disks for additional rigidness
- The design for guy “ears” was changed on the orbital bearing. Previously, there was a completely different design with two elements. Everything was greatly simplified … I very hope we haven’t made a major design mistake with that
- It is not obvious whether the metal is suitable at all – it may be too weak – and the stronger steel of the bearings will make deep threads in the supporting metal too quickly and it will be too difficult to rotate the tower and will stuck
In the last moment, I asked to weld a special support for the 6-meter jig pole that will be used to raise the bottom element of the tower. I cannot call for a crane for such a small work. Thus, some heavy lifting must be done using basic tools, with the help of a wincher, and by myself only. The support shall help with that.
On the opposite corner, we welded bottom elements for the rotator’s future support. Since China is finally back from its long Chinese New Year holidays, it is time to select and purchase the rotator. It will take about two weeks to arrive. By then, it would be great to install the tower or at least a few of its lower sections and see whether everything meets expectations.
Since the rotator has yet to be purchased, we made a base so that different types of mounting structures can be installed on it with drilling since welding won’t be available on the QTH.
In a parallel world of making the mast sections, scary news came:
- The guys who do the masts sections (7x6m) cleaned the tubes from the rusts and only then discovered that they are not 32 mm in diameter as they were supposed to be but 42 mm … I wonder how it is possible to confuse the 32-mm tube for the 42-mm tubes … either they are highly unprofessional or there is no proper control. Both options are not encouraging since I need to rely on the quality of the sections very much
- The design had to change on the fly as well since different diameter of the tubes will be used
- They will be stronger, which is good. But they will be heavier. Which is bad. I am not sure what is better
Since it takes so much time to assemble the orbital bearing, it was worth changing the design of the connection between the sections. The flange won’t be used as planned because it wouldn’t fit inside the diameter of the orbital bearing without the bearing disassembly. Instead, thicker outer tubes of 40-cm length will connect and hold the sections together.
It will also impact the design of the bearings. It will be simpler – not need to assemble – but more expensive because the inner disks will be just cut off and not used. But the disks will be flatter as well. So, the overall design will be better.
2025.Feb.01
Since the antenna is mainly done, I haven’t done much about it since the last visit:
- I sent multiple requests for the masts. A couple of prospects for production are identified. It’s not as great a factory as before, but it’s already something reasonable cost-wise and potential quality. Ready to order on Monday. But perhaps, I won’t hurry since a few elements for the rotator and orbital bearings shall be ordered along
- Order a crane. It is an easy option, but so far, the prices have not been appealing at all. If you check websites – more than comfortable, per/hour. But then you dig deeper, and they don’t offer per hour anymore but per shift, and if calculated per hour, it is 2-4 times more than advertised. I don’t like that kind of cheap lying. So, I’m still searching. Though, it is the most probable option as of now
- Since I put down and raised the tower yesterday, the next option is to use the same approach as with the 10-meter and 20-meter towers – tilt-up method. It is proven and worked. However, for the 40-meter tower, it may be a bad solution:
- Even for the 20-meter tower, using the winch is pretty tough. I am sweating a lot and need to rest several times before I raise the tower. The 8-mm guy sings is like a string. So, it is all close to limits. With the weight of the 40-meter tower, everything may be way beyond the limits, which is dangerous
- There is no point use it after the erection because there will be several antennas on the mast. Thus, I can’t put it down as now anyway. So, the usage will be different as compared to the 10-meter and the 20-meter tower, and the benefits for the option to put the tower down, fix something quickly, and raise it again are none or much smaller than with the existing towers
- To use the gin-pole method. It looks like a nice and independent option. However, it is pretty risky to erect section after section on a rotating tower with multiple levels for guys. Each section is relatively heavy. Everything may take a lot of time. It is much nicer to assemble everything on the ground and to climb the tower when everything is well set and secured with the guys to the ground
In short – many open questions. But the crane looks like the most viable option as of now. By the way, I studied how the wind towers are erected – cranes. Other options are there but cranes – that is what they use. Let’s do simple and proven.
We progressed well with the orbital bearing, though. The first design looks implementable and solid enough. I will be sending requests for quotations tomorrow; thus, some things may change, but the overall design so far looks OK. Of course, everything may change when the tower collapses. But, hopefully, it won’t 🙂
Besides, when I was climbing yesterday to fix the 20-meter and the 15-meter Yagi, the view to the 40-meter is impressive. It is like a newly hatched dragon that doesn’t yet know it can fly. 🙂
A model advertises the Yagi 🙂
2025.Jan.26
Sunday is the time to complete what has been started earlier.
Of course, I couldn’t not visit my friends 🙂
Elements missed the 4-meter tips from each side. It looked like an easy and straightforward work.
And then – the long-awaited steps – to connect the resonator to the cable and measure the SWR for the first time after nearly two weeks of making the antenna.
The frequencies are just fine. The SWR is a bit higher than wanted. However, the antenna is less than a meter from the ground. Thus, it is not yet a real measurement. But the moment is always very awaited 🙂
It is time to raise the antenna higher … and, as usual, the time is up … – the sunset 🙂
It is not a good idea to climb a slippery ladder… alone … at dusk … in winter … in the steppe … But we are unstoppable in antenna building … and not only 🙂
The second SWR measurement – just before raising the antenna – shows an even better SWR.
Problem 1: Connecting the antenna analyzer via a 5-meter cable immediately killed the nice SWR picture. I didn’t get it.
- Re-measured. The result is the same – not a flat frequency response and higher SWR
- Placed the cable along the boom – to make it perpendicular to the elements and minimize the potential impact. It didn’t help. The resonance wasn’t flat and the SWR wasn’t beautiful anymore …
The first attempt to raise the antenna ended after 5 seconds with a boom from above… luckily, the height wasn’t big. Nevertheless, my skull has got a new scar. Not a major one, but still – an unplanned 🙂
Low-quality things kill. Be careful.
Another hour or so was spent to install a new roller.
And, finally, the antenna is about 2 meters above the ground! 🙂
- The overall mechanics and rigidness is OK
- The front part is heavier. I will have to shift the center to balance the weight
- I didn’t dare to leave it higher because a 42-mm steel tube bent too easy
The starry beauty of the moment is difficult to describe in words.
Big open questions
- Is it really worth it? Alternative antenna variants, such as quads or vertical arrays, may be more reasonable. It took two weeks to assemble the antenna, which is a lot
- How to test it?… I quite freely modified the design using as a base the 10-meter version … But it assumes several iteration that involves easy raising and grounding the antenna …. but how? … – it is large and almost touches guys of neighboring masts… it is scratching its belly off the ground – it is not real tuning… Besides, tuning of SWR is great, but how do you test the gain before raising it to 20-40 meters of the ground? It is a too massive leap of faith. I prefer to measure and then dive into faith.
2025.Jan.25
Friday was lost because I am a family man, after all 🙂
Besides, it never hurts to do some work as well 🙂
However, Saturday came with many surprises. When I came, the wind was very strong. It is one story to calculate something and entirely another – to see how the antenna bends and rotates. It is worth experiencing that from time to time to keep an agile sense of harsh reality.
By the end of the day, I had the entire antenna assembled except for external tips – about 4 meters from each side. I really wanted to finish everything by the end of the weekend and do the first tests.
2025.Jan.23
There were a couple of days of heavy snowing, then the temperature dropped to -17C at night. Thus, I skipped those days.
However, as soon as the snow stopped, I went to the QTH to check on things. I was particularly concerned with the 20-meter antenna. I stopped receiving anything. It was either an issue similar to the 15-meter Yagi, which just disconnected somewhere, or perhaps the situation was more severe with the mast on the ground and all antennas collapsed under it. Since I haven’t installed any cameras yet, until I come, I can only guess.
The masts were OK. The antennas were in place; however, both 20-meter and 15-meter Yagis were cut off somewhere somehow… Well, I was busy with the 40-meter Yagi. Thus – one less destruction 🙂
And only the oldest babe – the 10-meter 6-element monoband has been working as well as always.
2025.Jan.21
Since the reflector with a pair of supporting guys (one on the left and one on the right) worked reasonably well, the task was to replicate that for the other three elements.
The radiator was slightly different because it had a cut in the middle. Thus, I decided to use 6+6 meter tubes in the middle and longer than other elements support П-shaped steel part holding the elements.
I used the 6-meter tubes. Thus, the front element must use 3+3m tubes in the middle. Well, I have to sacrifice a potentially more robust tube for the more important element – the radiator.
The next steps:
- To make guys and support the elements
- To add remaining elements to all tubes
2025.Jan.20
I tried the new set of tubes, and it worked reasonably well:
- 2 x 2 x (3000x32x2) – sections around the boom are solid
- Maybe it is even better to have 2 x (6000x32x2)
- The next sections – closer to the tips are better to be shorter and falling in diameter quicker. I am not yet reducing the diameter as quickly as my role model. They start from 48mm and end with 8mm. I start with 32mm and end with 10mm. Their profile is better, I believe. However, I couldn’t get anything larger than 32mm. Thus, reality shapes the design 🙂
- After the change, I tend to think that even a single guy per 1/2 of the element may be sufficient. Surely, it won’t be as robust as with two guys per half of the element, but adding the second guy closer to the tip doesn’t bring much rigidness to the element – rather, it bends it. Bending the external part with the second guy, bend the inner part of the element as well. Thus, adding the second guy creates more harm than help: bending, weight, wind resistance, impact on the radiation pattern, labor efforts
With the new variant of the set of tube:
- The overall shape of the 23-meter element (potential length of the reflector) reminds the seagull’s wind profile. It is certainly not an arrow. But! It looks like a reasonable compromise regarding available options, weight, wind resistance, and straightness of the element
- For example, the 20-meter 4-ele monoband Yagi doesn’t have any support for elements at all, and the tubes are smaller and thinner. The tips bent down by their weight by a meter, at least. However, the antenna survived a few pretty aggressive storms last summer (though bent mercilessly during the gusts). Performance-wise, I am very happy with the antenna: gain, front-back, and front-side
- The overall deviation from the horizontal line is about ±30cm. It goes a bit up where the guys hold the end of the inner 3+3 meter sections and going down to the end of the tip, which is not supported by the second guy any more in this design
Thus, I will take risks and continue with the design. Next steps:
- To repeat the same operations with three more elements, including the resonator
- Put the antenna down on the ground
- Install the winch on the same 6-meter tube
- Raise the antenna a few meters over the ground using the winch
- Start tuning the antenna to the proper frequency using the antenna analyzer
- Verifying that the guessed dimensions are OK with the real gain measurements, front-back and front-side measurements in the air. If the dimensions are not optimal, it is possible to shift the elements along the boom quite comfortably since they are not bolted to the boom
Other elements are shorter than the reflector. Thus, the expected bending is lower and rigidness – higher.
2025.Jan.17
It had been too smooth so far: all components were in place, there was no urgent need to rush to a market and lose time, and everything fit and worked OK … – this is not good … – it means that the hit will be strong and late – when little can be changed or adjusted and you must go to the square one more or less … 🙂
Yesterday, I started feeling that I was about to hit the rock when the element was in the air, even with the guy attached to it wobbled and bent. It means that the tubes of the element have too little diameter, they are too thin… it means that all design of the elements is just wrong … that is not good at all.
Highlights of the day:
- The vertical part supporting the elements is solid and doesn’t look like a problem
- The boom guys easily hold the weight of the reflector
- The first 6 meters of the reflector is OK but slightly bent. Bent but slightly
– The elements are too thin. Thus, even when I am using a guy, the guy doesn’t make the element straight but bends it- When the last 5 meters are bent, they bend the first 6 meters as well, and the whole reflector collapses…
It is a major problem … not yet a disaster but it is a major problem. Possible solution:
- To make more rigid elements. First, I thought to make 25×1.8 mm instead of 19×1.5 mm but now I think to extend the 32×2 mm part by 3 meters
- Thus, the new table shall look like this:
2025.Jan.16
Highlights of the day:
- The boom is stable and solid even with two guys. Smaller guys will make the whole structure even more rigid. Not too much worries about that part of the antenna. Yet 🙂
- I discovered the electric lighting thus extending the working time beyond the sunset that happens way too soon – around 16:30. But 5pm, it is completely dark
All these reminds me solo diving under ice:
- You are alone in a strange place … open field is not that much different from an open sea
- It is dark
- You do something technical that requires attention and focus
- It all is not very convenient to do alone thus basic operations take time
- You are not talking to anyone and remain in own thoughts that flow through you with their own pace
2025.Jan.15
I made notes on building the 10-meter Yagi.
But I was too busy (lazy) to record the steps on the 20-meter Yagi and then the 15-meter Yagi … and that is lost forever.
Before I forget, I will try to record thoughts, ideas, and steps while designing and building the 40-meter Yagi.
I am starting recording before I know the results. Maybe it is a major mistake. Maybe I will break my neck literally since the antenna is huge and the tower is insanely tall (I hope not :-).
I hope to enjoy the process and the result and help others with ideas.
Meanwhile, Tony (3D2AG) sends from Rotuma 🙂
2025.Jan.14
2025.Jan.13
This project includes several sub-projects:
- Building the Yagi
- Building a tower
- Building a rotator and bearings
- Designing the tower erecting process and erecting the tower. Raising the antenna to the tower
I have spent 1-2 weeks heavily studying and calculating. At the end, I had 3 detailed Excel sheets with calculations, links, ideas, photos from other projects.
Some key references:
- https://antennas-amplifiers.com/40m-full-size-4el-yagi-antenna-pa7-4-18hd/ – I like the solution, the approach – many hints are taken from this design
- http://on5au.be/content/a10/ant36.html – the main source for initial dimensions before scaling
- https://www.w8ji.com/Rohn%2065G%20project.htm – hints of what is doable and what big boys do
- http://www.k3lr.com/Hardware/ – ideas from big boys
- https://www.w8ji.com/rotating_tower_w8ji.htm – on rotating tower and raising the antenna to the top
- https://youtu.be/ZzeB3FBY7Ik?si=LyOIB3kJrZtMt2cc – on rotating tower, erecting the tower, other hints
Many questions before start
How big to go
As of today (2025.Jan.15), I still don’t know what the tower will be… It certainly will be 20 meter or more… but how much more … 30 meters, 36 meters, 42 meters – I have only some vague ideas.
I have already moved to build the 4-ele OWA Yagi, so this is the first design I know of. Whether it is mechanically sound or implementable, I’m not sure yet.
Tower size
Would it be 40cm on each side?… 50cm? Triangle? Square? 6-meter sections? Or 6-meter sections and then 3-meter sections?
How to erect the tower
- I erected the tiny 10-meter alone using the gin pole method
- With the help of a few friends, we erected the 18-meter tower for the 20-meter Yagi using the same method. Even more, after special add-ons, I can lower and raise the tower with antennas on it all by myself
- But a 30- or 40-meter tower is too tall for that … Using a crane? Or should I raise the first 18 meters with the gin pole method and then gradually add a 3-meter section one by one?
- Or use a crane like the Irish did?
To build the concrete base or not
I have never done anything with concrete. At all. And I rent a plot on a farm for the QTH … it may be not a good idea to destroy the plot … but erecting a 40-meter tower without a concrete base is maybe the worse idea …
To build one or many antennas on the tower. A rotatable tower or a rotator
The tower is a huge investment of money, time, effort, and space. I want to try a stack or two on it.
I built a regular tower. A rotating tower sounds like a nice challenge. Whether it is doable and reasonable – I don’t know yet (2025.Jan.15). But after thorough checking of inner desires – that is the driving whim 🙂
If the tower is rotating, then the rotator and orbital bearings are things of their own
These things are complex, heavy, and expensive. The best hints and ideas:
- https://youtu.be/ZzeB3FBY7Ik?si=LyOIB3kJrZtMt2cc – again the friends from Ireland
- https://ant-depot.ru/catalog/povorotnye-ustroystva/ra4lw-ring-rotator/?oid=58991 – rotator
- https://www.oh8lq.com/index.php/making-towers-and-antennas?view=article&id=18:guy-rings&catid=2:uncategorised – found on Feb.17., 2025 – much later than I started designing
How to lift the antenna
Many technical decisions are closely interlinked. Lifting the antenna to the tower is one of the key steps.
What materials to use
After reading, studying, and calculating, АМг5 or АМг6 or АМг5M or АМг6M were selected…
After getting the first quotations and budgeting the idea, I scaled back to my noname supply from a local noname market of a noname alloy 🙂
I have been hinted that the tubes I finally purchased can be the 6063 alloy. But that is unconfirmed. Well, I again build from what I have – not from what I would like to build 🙂
It is valid not only for the alloy but also for the dimensions of tubes for elements and for the boom.
Eventually, I purchased the following volume for elements:
For the boom and the support:
- 6000x50x50x2 – 3 pcs. I thought to buy an additional piece as a central element for more strength. But this tube was the most expensive, and I thought I would buy it later if needed. Though delivery to the QTH, which is 60 km away, can be expensive, purchasing something I may not need was expensive too …
- 6000x30x30x2 – 3 pcs for boom support and for elements support
