When do I need a sheathing wave blocker?

You need a sheath wave barrier, also known as a balun or ferrite core, in amateur radio to prevent unwanted sheath waves that can flow along the outer conductor of your coaxial cable. These waves can cause interference by propagating back down the cable to the transmitter, distorting the antenna pattern or causing unwanted emissions. A standing wave barrier becomes particularly important when: 1. You are operating an asymmetrical antenna system, such as an end-fed or vertical antenna, where the currents on the coaxial cable shield and the antenna do not balance and sheath waves are more likely. 2. You notice RF problems in your own or neighboring electronic devices, which indicates that the RF signal is being returned through the cable. 3. You are working on multi-band antennas where the harmonics of one band frequency can cause interference on another band. By using a standing wave barrier, these problems can be minimized and the performance of the antenna can be optimized as well as electromagnetic interference can be reduced.