# What is the purpose of a balun and a unun in a feed line?

I have never understood how a balun or a unun works and under which situation I need to use either of them in an antenna feed line.

An unun is an impedance transformer, usually 4:1 or 9:1, which matches an unbalanced antenna to a feedline. A 9:1 transformer is often used for an end-fed half wave antenna.