Guanella balun was invented by Gustav Guanella, a Swiss engineer as a "New method of impedance matching in radio-frequency circuits" in 1944. Balun stands for balanced line to unbalanced line. It is typically connected between a balanced antenna and an unbalanced feeder coaxial cable. Balun is a type of transformer. A 1:1 balun will connect to a 50 Ohms unbalanced line and present a balanced output at 50 Ohms. In its simplest form, a 1:1 Guanella balun is an RF choke which presents a high impedance to the unablanced current flowing on the external aspect of the shield or outer conductor of the coaxial cable. This will force RF energy to and from the antenna to flow only through the inner conductor and the inner aspect of shield, thus providing best efficiency to the radio.
