Micrometals Iron Powder Toroids – Selection Guide
Micrometals iron powder toroids are essential components for RF applications, filters, baluns, and inductors. This guide will help you choose the right model for your needs.
Comparison Infographic
How to Choose the Right Toroid
- Operating Frequency: Each mix is optimized for a specific frequency range.
- Size: Indicated by the code (e.g., T50-2 = 0.50” diameter, mix #2).
- AL Value: Useful for calculating the desired inductance.
Micrometals Materials Table
| Material | Reference Permeability |
Powder Type | Temp Coefficient of Perm (+ppm/°C) |
Density (g/cm³) |
Max Frequency (MHz) |
Color Code Toroid |
|---|---|---|---|---|---|---|
| -0 | 1 | Phenolic | N/A | N/A | N/A | Tan/Tan |
| -1 | 20 | Carbonyl Iron | 280 | 6.4 | 10 | Blue/Clear |
| -2 | 10 | Carbonyl Iron | 95 | 5.0 | 45 | Red/Clear |
| -3 | 35 | Carbonyl Iron | 255 | 6.5 | 5.0 | Gray/Clear |
| -5 | 5 | Carbonyl Iron | 280 | 5.0 | 10 | Green/Clear |
| -6 | 8.5 | Carbonyl Iron | 35 | 5.0 | 55 | Yellow/Clear |
| -7 | 9 | Carbonyl Iron | 30 | 5.0 | 50 | White/Clear |
| -8 | 35 | Carbonyl Iron | 255 | 6.5 | 5.0 | Yellow/Red |
| -10 | 6 | Carbonyl Iron | 150 | 4.9 | 83 | Black/Clear |
| -15 | 25 | Carbonyl Iron | 190 | 6.4 | 7.0 | Red/White |
| -17 | 4 | Carbonyl Iron | 50 | 4.8 | 170 | Blue/Yellow |
Materials ‑2, ‑5, ‑6, and ‑7
These are the most popular carbonyl iron mixes. They offer a high Q up to 40 MHz and are widely used in amateur radio and various communication applications. They are also suitable for moderate-band transformers operating in the 200 to 400 MHz frequency range.
Materials ‑1, ‑3, ‑8, and ‑15
These materials are annealed carbonyl irons with the highest permeability among carbonyl types. They are ideal for high Q applications below 1 MHz and for broadband transformers typically covering the 50 to 500 MHz range.
Materials ‑10 and ‑17
These are the highest frequency carbonyl iron materials . They provide a high Q up to 150 MHz and are commonly used in cable television applications . They are also suitable for moderate-band transformers operating between 400 and 700 MHz .
Material ‑0
This is a non-magnetic material used as a solid winding form for air-core coils. It offers excellent temperature stability and a high Q at the highest frequencies . It is also useful for moderate-band transformer applications typically covering the 600 MHz to 1 GHz range.
Example Products
- T25-2: 0.25–20 MHz – ideal for HF baluns
- T30-6: 3–40 MHz – great for RF filters
- T37-17: 20–200 MHz – for VHF circuits
Inductance Calculation
Use the following formula to calculate inductance:
L = AL × (N² / 100²)
Where L is the inductance in µH, AL is the toroid's AL value, and N is the number of turns.
