Predicting Balun Performance Using 3-D Models

After I retired and got back into ham radio, I put up an 88-foot dipole fed with 45 feet of home-brewed ladder line. W2FMI’s book [Ref. 1] inspired me to make my first balun, which I named “Balun #1” (Photo A).¹ I connected Balun #1 between my external antenna tuner and the ladder line, and I made lots of contacts on the HF bands. Balun #1 worked well, but I wasn’t sure it was the best design, so I looked into a model-based simulation as a way to answer some questions:

1. What’s the best way to connect a balun and a tuner?

2. What leads to power loss in baluns and how much is lost?

3. Can models predict the characteristic impedance of the balun’s wound transmission line?

4. What ferrite material works best over the HF range?

5. Can models predict the Common Mode Rejection Ratio (CMRR)?

6. Do baluns wound with coax or made with ferrite beads work as well as wire-wound baluns?

Making a realistic 3-D balun model requires a CAD program able to characterize the physical and material properties of wires, cores, enclosures, and ground planes. The program carries out swept frequency simulations that predict how the physical balun will perform. I used EMCoS Studio, a comprehensive electromagnetic system simulator [Ref. 2]. EMCoS Studio’s libraries describe the properties of materials used in balun construction, and it models the skin effect, which causes wire losses to increase with frequency. I obtained data from Fair-Rite, Inc. to characterize types 31, 43, 52, and 61 ferrite materials [Ref. 3].

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Building the 3-D model involves several steps:

1. Create a dimensioned geometric drawing. The EMCoS program provides a set of built-in shapes and tools that a designer uses to create a drawing. The program allows