Cont
There are two basic ferrite material groups: (1) Those having a low initial permeability (μi) range from 20 to 850 µ (permeability) that are of the Nickel Zinc (NiZn) class (mixes 43, 52, 61); and (2) those having a high initial permeability (μi) above 850 µ are usually of the Manganese Zinc (MnZn) class (mixes 31, 73, 75, 77).
The Nickel Zinc (NiZn) ferrite cores (mixes 43, 52, 61) have low initial permeability (μi), exhibit high volume resistivity (high ohmic core surface resistance), moderate temperature stability and high ‘Q’ factors (figure of merit or level of operational performance) in the 500 KHz to 100 MHz range.
They are well suited for low power, high inductance, resonant circuits. Their low permeability factors also make them useful for broadband transformer applications (baluns, ununs, chokes). Nickel-zinc ferrites have a higher resistivity and are used at frequencies from 2 MHz to several hundred megahertz. The exception is common mode inductors where the impedance of NiZn material is recommended for use from 70 MHz to several hundred GHz.
The MnZn ferrite cores (Mix 31, 73, 75) have high initial permeabilities (μi), that are above 800 µ, have fairly low volume resistivity (low ohmic core surface resistance), and moderate saturation flux density. They offer high ‘Q’ factors for the 1 KHz to 1 MHz range. Cores from this group of materials are widely used for switching mode power conversion transformers operating in the 20 KHz to 100 KHz range. These cores are also very useful for the attenuation of unwanted RF noise signals (line or CM chokes) in the range of 2 MHz to 250 MHz. Manganese-zinc ferrites are generally used in inductor applications where the operating frequency is less than 5 MHz. The exception is common mode inductors where the impedance of MnZn material makes it the best choice up to 10 MHz.
What’s Different between Mixes? The “Mix” is the chemical formula of the iron oxide. Ferrite is a actually a sintered, ceramic compound consisting of iron oxide and generally either of two types of ceramic (Google sintering for the definition):
- Manganese-zinc (MnZn) is available as Mixes 31, 73, 75 and 77 (and others) and work well for common mode chokes
- Nickel-Zinc (NiZn) is available as Mixes 43, 52, and 61, (and others) and are the preferred material for baluns and ununs.
Palomar Engineers uses mix 31, 43, 52, 61, 73, 75 and 77 for most applications from RFI/EMI common mode suppression; multi-ratio toroid baluns and ununs; and sleeve baluns for line isolation. Each mix number has a measurable permeability and suggested frequency range for certain applications.
Table 1. gives our recommended applications for various mixes and effective frequency ranges
| Mix # | Material | Initial Permeability μi | RFI/EMI Common Mode Suppression Range | Tuned Circuits – Coil | Wide Band Transformer (Balun & Unun) |
| 31 (1) | MnZn | 1,500 | 1-300 MHz | – | 1:1 only, <300 MHz |
| 43 (2) | NiZn | 800 | 25-300 MHz | < 10 MHz | 3-60 MHz |
| 52 (6) | NiZn | 250 | 200-1000 MHz | < 20 MHz | 1-60 MHz |
| 61 (3) | NiZn | 125 | 200-1000 MHz | <100 MHz | 1-300 MHz |
| 73 (7) | MnZn | 2,500 | < 50 MHz | < 2 MHz | <10 MHz |
| 75/J (4) | MnZn | 5,000 | 150 KHz – 10 MHz | < .75 MHz | .1-10 MHz |
| 77 (8) | MnZn | 2,000 | 200 kHz – 15 MHz | <4 MHz | .5-8 MHz |
Table 1.
Notes:
(1) Mix 31 excellent for 1-10 MHz common mode suppression, then performs similar to 43 up to 250 MHz. It is NOT recommended for multi-ratio impedance transformers (baluns/ununs) due to material characteristics and power handling capability but OK for ham radio 1:1 feed line chokes. Its Curie temperature is >130 C (temperature above which the magnetic properties begin to fail and permanently destroys the usefulness of the core). Mix 31 is available in TOROIDS, SLIP ON BEADS, and SNAP ON SPLIT BEADS
(2) Mix 43 is excellent for common mode chokes from 25-300 MHz, Use Mix 31 below 10 MHz for higher choking impedance. Curie temperature >130 C.. Mix 43 is available in TOROIDS, and SLIP ON BEADS
(3) Mix 61 will withstand high power in multi ratio (2:1, 4:1, 9:1) impedance transformers (baluns/ununs). Currie temperature > 300 C. Mix 61 is available in TOROIDS, SLIP ON BEADS, and SNAP ON SPLIT BEADS
(4) Mix 75 (also known as Mix J) Beads only. Go to Palomar Engineers link above for applications.
(5) There’s no footnote 5.
(6) Jerry Sevick, W2FMI’s broadband transformers (baluns/ununs) used a permeability of 250 (Mix 52). The F240-52 ring toroids are ideal for replicating his designs. For a free archived download of his book, “Transmission Line Transformers Handbook, 48 Improved Designs”, paste this link into your browser: Ham Radio Transmission Line Transformers Handbook
(7) Mix 73 is only available in small bead size from Palomar but exists elsewhere in standard sizes, for larger inside diameter requirements use Mix 77.
(8) Mix 77 has a much lower permeability of 2,000 instead of 5,000 like mix 73. I cut and pasted the relevant data for 77 mix into Table 1 that I copied from Fair Rite.
General Comments On Frequency Ranges And Application
When selecting a mix to use for tuned circuits or broadband transformers, the frequency range should allow for operation in the INDUCTIVE range of the ferrite mix frequency curve. For best results use the proper mix with a RESISTIVE-dominant range for RFI/EMI suppression at the fundamental RFI frequency. Additionally, Mix 31 is only appropriate for 1:1 impedance (CM) transformers and for RFI suppression from 1-300 MHz; it should not be used for <1:1 or > 1:1 impedance transformers as the material resistivity is high when used above 5 MHz.
We have experienced excellent RFI common mode suppression under 5 MHz with mixes 75 and 77 when using multi-turn toroidal topology (translated, 1:1 Guanella current balun. Transformer construction will be covered later.)
Part 2 will continue with more details on core selection and winding with regards to frequency, and power handling capability, plus enclosures, plus lots of other useful stuff.
