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.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.
Day 3
Meanwhile, Tony (3D2AG) sends from Rotuma 🙂
Day 2
Day 1
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
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
