What is a Bazooka Balun?

What is a Bazooka Balun?

Balun stands for balanced line to unbalanced line, typically connected between a balanced antenna and an unbalanced feeder coaxial cable. Bazooka balun is a sleeve around the coaxial cable, short circuited to the outer surface of the shield and resembles a bazooka. It is also known as a sleeve balun. Bazooka balun increases the impedance to ground seen by the outer shield current and minimizes the outer shield current. Sleeve of the bazooka balun can be made of an aluminium tubing used for UHF antenna. Bazooka balun can be implemented between the dipole element of a UHF Yagi-Uda antenna and the feeder coax.

Length of the external sleeve in bazooka balun is quarter wavelength and it is grounded to the outer surface of the coax shield, away from the dipole antenna feed point. Inner conductor of the coax and outer shield of the coax at its end are connected to the dipole antenna feed points. The shorted combination of quarter-wave sleeve and outer surface of the coax shield presents infinite impedance and the RF current flows only on the inner surface of the coax shield, thus making it a balanced transmission line.