Multiband vertical antenna
Building a 7.6-meter multiband vertical for 80-10m with a 4:1 Un-Un
Description
Constructing an effective multiband vertical antenna for HF operation, this resource details the build of a 7.6-meter aluminum vertical with a 4:1 Unbalanced-Unbalanced (Un-Un) matching unit. It provides specific instructions for assembling the aluminum tubing elements, winding the Un-Un on an Amidon T200-2 toroidal core with 19 turns of 0.75 mm diameter wire, and integrating the matching unit at the antenna base. The article includes material specifications, such as four 2-meter aluminum tubes of varying diameters (35, 30, 25, 20 mm) and an external electrical box for the Un-Un housing, ensuring a robust fixed station installation.
The practical application section presents detailed performance observations over two years, including comparative analysis against a Windom and a multiband dipole. The vertical consistently outperforms the wire antennas on 10, 15, 20 meters, and the WARC bands, while the wire antennas show better performance on 40 and 80 meters due to their length. The antenna exhibits a Standing Wave Ratio (SWR) below 2:1 across most bands, with near-null values on 28, 18, and 10 MHz, only requiring an antenna tuner on 80 meters where SWR exceeds 3:1. Specific SWR values are provided for 10, 12, 15, 17, 20, 30, 40, and 80 meters, noting slight variations when the ground is wet.