Ferrite Mixes on HF: Chokes vs. Broadband Transformers

Ferrite Mixes for HF: Which Material Does What — And Why

Ferrite “mix numbers” (31, 43, 61, 75, 77, 73, etc.) are not random. Each mix has a specific magnetic behavior and intended purpose. Some mixes are perfect for HF broadband transformers, some for common-mode chokes, and others should be avoided entirely in the HF range.

This article explains which mixes work for what — and just as importantly: why certain mixes should never be used in HF transformer designs.

The Two Main Ferrite Jobs in HF Radio

Common-Mode Chokes

Goal: block unwanted RF on coax shields or control cables.

Choke ferrites should be:

• lossy at the operating frequency (RF energy is turned into heat)
• high permeability to raise common-mode impedance

This is why mixes like 31, 73 and sometimes 75/77 excel at choking.

Broadband HF Transformers (Baluns / UNUNs)

Goal: efficiently transfer power across HF bands.

Transformer ferrites must be:

• low-loss at HF (otherwise the core heats up)
• higher Q than suppression ferrites
• permeability that stays stable across HF

This is why Mix 43 is the universal HF transformer material — and why Mix 31 must never be used as a broadband transformer core.

Ferrite Mixing Guide — All Relevant Materials

Mix 31 — HF Common-Mode Choke Material

• High permeability
• Broadband suppression from LF → HF → low VHF
• Resistive loss profile ideal for choking

Correct use: HF common-mode chokes

Do NOT use for: HF transformers, baluns, UNUNs (too lossy, saturates early)

Mix 43 — HF Broadband Transformer Material

• Lower loss at HF (compared to 31/73)
• Stable μ across 1–30 MHz
• Excellent transformer performance on 80–10 m

Correct use:

• Broadband 1:1, 4:1, 9:1, 16:1, 49:1 transformers
• Power baluns up to high HF

Do NOT use for: low-frequency chokes (insufficient μ for 160 m unless many turns are used)

Mix 52 — High-Frequency Transformer Mix

• Lower permeability than 43
• Low loss at upper HF / low VHF

Correct use: high-frequency transformers (20–10 m), VHF baluns

Limitations: not ideal for 160/80 m magnetizing inductance without increasing turns

Mix 61 — VHF/UHF Inductor Material

• Very low permeability
• Low loss at VHF/UHF

Correct use: VHF/UHF inductors, resonant circuits

Do NOT use for: any HF balun or HF choke (μ too low, unusable for HF transformers)

Mix 73 — Low-Frequency Choke Material

• Very high permeability
• Strongly lossy at RF

Correct use: Low-frequency chokes (LF/MF/HF), feedline isolation for 160 m, longwire CMC reduction.

Not suitable for: HF transformers (far too lossy — will overheat immediately)

Mix 75 / Mix 77 — LF/MF Materials

• Extremely high permeability
• Optimized for LF and MF frequencies

Correct use: Very-low-frequency chokes (LF/MF)

Not suitable for:

• HF broadband transformers — saturate and overheat
• High-power HF chokes — too lossy and unpredictable above low HF

Ferrite Mix Selection Table

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