What determines the performance of a ferrite core at different frequencies?

Ferrite cores are magnetic components used extensively in amateur radio for making baluns, chokes, and inductors. They are made from ceramic materials blended with iron oxide and other metallic elements like zinc, manganese, or nickel. The specific recipe of these materials is referred to as the 'mix.' Different mixes are engineered to have specific magnetic properties (permeability) and loss characteristics that are optimal for different frequency ranges. For example, a Type 31 mix is excellent for HF chokes, while a Type 43 mix is better for broad-band transformers. Physical dimensions like thickness or diameter ratio do affect the total inductance and power handling capacity, but it is the chemical composition (the mix) that dictates the core's frequency response and overall suitability for a given band.