The objective of a choke balun is to reduce RF current flowing on the outside of the coaxial cable, thereby improving the symmetry of the radiation pattern and suppressing radio-frequency interference (RFI).
A couple of weekends ago, I took my trapped vertical antenna apart to clean it up, ensure every component was in good working condition, and fine-tune it. While working on the antenna, I noticed that the Common Mode Current choke box had a crack due to the hot California summer …