What is a Ferrite ring and what is it used for?

Ferrite looks like a ceramic with magnetic properties, It is used in many electronic devices. Chemically, it's M(Fe(sub x)O(sub y)), M being any metal that forms divalent bonds.

Ferrites have very high magnetic permeability and electrical resistance. The high magnetic permeability is important in high frequency devices such as antennas.

Ferrite Rings are used as cores for homemade Transformers. This type of experiment and construction is very common in Ham Radio.