Toroid mix plays a critical role in the design and performance of baluns and common-mode chokes, especially in ham radio and RF applications. The key to effective performance lies in choosing the correct mix of ferrite material for your operating frequency and intended use.
Different mixes offer different magnetic properties, affecting impedance, loss characteristics, and frequency response. While all toroids look similar, what’s inside determines how they behave in real-world circuits.
Mix 31: A Broad Range Performer for Common-Mode Suppression
Mix 31 is a popular ferrite mix for low-frequency to mid-HF applications. Its standout characteristic is its ability to provide high impedance at lower frequencies. This makes it an excellent choice for common-mode chokes on HF antenna feedlines, power cords, and audio cables.
Moreover, Mix 31 excels at absorbing unwanted RF energy, particularly below 10 MHz. Because of this, it’s ideal for dealing with common-mode currents on HF bands. Especially for the 80m and 160m amateur bands. However, above 30 MHz, its performance quickly deteriorates. Therefore, it’s not suitable for VHF or higher-frequency applications.
One drawback of Mix 31 is its relatively high core loss at higher power levels. So while it offers good suppression, care must be taken with power handling to avoid core heating or saturation.
Mix 43: Versatile but Not Specialized
Mix 43 is perhaps the most commonly available ferrite mix and often serves as a general-purpose material. It works reasonably well from 10 MHz to 250 MHz, though its peak performance lies between 25 and 100 MHz. Because of this, it finds use in VHF suppression, moderate HF applications, and RF filtering on cables and transmission lines.
Although many use Mix 43 for HF chokes, it’s not as effective as Mix 31 at lower frequencies. That said, it still performs adequately in the 40m to 10m ham bands. Furthermore, its availability in various sizes makes it an accessible choice for experimenters and builders.
On the downside, Mix 43 tends to exhibit modest impedance in the lower HF range and doesn’t suppress as well as Mix 31 in that region. In addition, its loss curve performs poorly in higher-power HF applications, and using the wrong core size can lead to saturation issues.
Mix 52: Better for Higher HF and VHF Work
Mix 52 is less commonly discussed but provides useful performance in the HF to VHF transition range, specifically from 10 MHz to 300 MHz. It exhibits lower loss at higher frequencies compared to Mix 43, and delivers better impedance over a broader upper-HF range.
Because of its characteristics, Mix 52 is suited for high-frequency RF chokes and baluns in the 15m to 10m amateur bands, as well as low VHF. It also works well in baluns for broadband antennas, where efficiency at higher frequencies is important.
However, Mix 52 is not optimal for low HF bands like 80m or 160m. Its impedance drops significantly in the lower spectrum. This makes it a poor choice for those looking to suppress common-mode current at low frequencies. Additionally, mix 52 can outperform both Mix 31 and 43 in terms of efficiency and reduced heat generation.
Mix 61: Excellent for VHF and Low-Loss Applications
Mix 61 offers low-loss performance and excels in high-frequency applications, typically working best between 100 MHz and 500 MHz. Engineers frequently use it in baluns for VHF/UHF antennas, wideband transformers, and filters that demand minimal core loss.
One key advantage of Mix 61 is its very low power loss, even under higher power levels. This makes it suitable for applications requiring minimal insertion loss, such as transmitting baluns or impedance transformers in VHF systems.
Although Mix 61 performs well at higher frequencies, it delivers poor results in the lower HF range. It offers limited impedance below 30 MHz and fails to provide effective common-mode suppression at those frequencies. For HF work, it’s simply the wrong material unless paired with other mixes or cores.
Mix 77: Optimized for Low Frequencies and Common-Mode Control
Mix 77 is engineered for very low-frequency applications, offering extremely high permeability. This allows it to provide high inductance with fewer turns, making it ideal for low-frequency common-mode chokes, RFI filters, and power line filtering. It performs best below 10 MHz, with peak impedance typically occurring in the 500 kHz to 10 MHz range.
In ham radio, Mix 77 works well for 160m and 80m band baluns and chokes, especially where long coax runs are prone to RF feedback. Its high permeability also means fewer turns are needed to achieve high impedance, which can help reduce wire losses and simplify construction.
However, Mix 77 has a weakness in power handling. It is not suitable for high-power RF applications, as the core can saturate or heat rapidly. It also loses effectiveness at higher frequencies, becoming almost useless above 30 MHz.
Therefore, while it’s great for EMI suppression at low frequencies, it’s a poor choice for VHF or high-power transmission lines.
Choosing the Right Mix for Your Project
Selecting the right toroid mix is not just about frequency, it’s also about the type of interference or signal behavior you’re trying to manage. For example, if you need a high-impedance choke for the 160m band, Mix 31 or 77 will serve you well. On the other hand, for a balun feeding a 2-meter antenna, Mix 61 will outperform every other mix.
Additionally, consider factors like core size, number of turns, and expected power levels. Some mixes require more turns to achieve the same impedance, and not all are suited for high-power RF without risking core saturation.
A general guideline for toroid mix:
- Use Mix 31 for low-HF common-mode chokes
- Use Mix 43 for general-purpose HF and VHF suppression
- Use Mix 52 for higher HF and lower VHF baluns
- Use Mix 61 for VHF/UHF, low-loss applications
- Use Mix 77 for low-frequency EMI suppression and low-power HF chokes
Final Thought
Understanding toroid mix characteristics is essential for building efficient, purpose-driven baluns, Ununs, and chokes. While no single mix is perfect for all scenarios, selecting the correct material based on frequency, application, and power level ensures optimal performance.