Vertical J-Pole for motorcycle use

This article describes the construction of a J-pole vertical antenna designed for motorcycle use, specifically to replace a previous bi-band antenna that interfered with a top case. The antenna is easy to build and mounts on the side of the motorcycle's trunk. It utilizes an aluminum angle bracket bolted to the lateral support, with holes for antenna passage, fixation, and BNC connector. The base is made from an 8mm threaded rod bent into a U-shape, measuring approximately 40mm wide. Coaxial cable connections are made via eyelets secured by 3mm screws to flattened sections of the rod. A 10mm aluminum tube is fitted onto the threaded rod, with a screw ensuring contact with the coaxial cable's core and securing the radiating element. Testing achieved a SWR of 1.2 across a significant portion of the band, improved by optimizing the coaxial braid contact point. The design prioritizes robustness against vehicle vibrations over precise SWR adjustment with sliding collars. The antenna can be painted or left with an aluminum finish.