Uploaded September 2021 | Updated September 2026, 2 weeks ago
This first video shows you how to build both a 4:1 transformer and a 1:1 choke current balun. Both are used in off-centre fed dipoles and loops (with a feed point impedance of around 200 ohms). The 1:1 choke can also be used on dipoles and doublets at the ATU.
For the design of the transformer and balun, my thanks go to Peter aka TRX Lab on YouTube. His comprehensive explanation of the build and testing in a professional lab can be found in part 3 of an excellent series of videos - Part 3: youtu.be/P7wW4TtXmc8 (I recommend you watch all three parts!). Peter's tests go to show that choosing the correct wire is one of the critical elements to success. Other transformers and baluns may look the part, but completely underperform when tested.
I sourced my handy-sized 2x1m (red & black) wire lengths here in the UK at: hobbyrc.co.uk/18-awg-flexible-silicone-wire-black-red-1m-2
The ferrites used in this build are type FT-240-43 from Fair-Rite. These can be sourced from various well-known suppliers, but ensure the mix is correct.
Part 2 shows the build of the 40m OCFD, plus on-air tests and tuning: youtu.be/llW4qJTHiv8
This is one of many amateur/ham radio related videos on my channel. Please feel free to browse 👀, like 👍🏻 and subscribe 🔔, remembering to hit the bell so you’re notified of new videos as soon as they're published and you don't miss out.
0:00 Introduction
1:34 Balun & Transformer Build
5:15 Summary Diagram
6:00 Bench Testing
8:30 Summing Up
Thanks.
Ian.
This first video shows you how to build both a 4:1 transformer and a 1:1 choke current balun. Both are used in off-centre fed dipoles and loops (with a feed point impedance of around 200 ohms). The 1:1 choke can also be used on dipoles and doublets at the ATU.
For the design of the transformer and balun, my thanks go to Peter aka TRX Lab on YouTube. His comprehensive explanation of the build and testing in a professional lab can be found in part 3 of an excellent series of videos - Part 3: youtu.be/P7wW4TtXmc8 (I recommend you watch all three parts!). Peter's tests go to show that choosing the correct wire is one of the critical elements to success. Other transformers and baluns may look the part, but completely underperform when tested.
I sourced my handy-sized 2x1m (red & black) wire lengths here in the UK at: hobbyrc.co.uk/18-awg-flexible-silicone-wire-black-red-1m-2
The ferrites used in this build are type FT-240-43 from Fair-Rite. These can be sourced from various well-known suppliers, but ensure the mix is correct.
Part 2 shows the build of the 40m OCFD, plus on-air tests and tuning: youtu.be/llW4qJTHiv8
This is one of many amateur/ham radio related videos on my channel. Please feel free to browse 👀, like 👍🏻 and subscribe 🔔, remembering to hit the bell so you’re notified of new videos as soon as they're published and you don't miss out.
0:00 Introduction
1:34 Balun & Transformer Build
5:15 Summary Diagram
6:00 Bench Testing
8:30 Summing Up
Thanks.
Ian.
