160m - 80m Transmit Vertical

This resource details the conversion of an 80m elevated vertical antenna to include 160m operation, focusing on a relay-switched design over a trap-based approach. It presents specific feedpoint impedance values, such as 32 ohms for 80m and 14 ohms for 160m, and discusses the challenges of SWR drift encountered with the prior trap system during RTTY contesting. The article thoroughly explains the design choices for elevated radials, referencing N6LF QEX data to debunk common myths regarding radial length and height, demonstrating that non-resonant radials can offer superior current uniformity.

The construction section provides practical insights into building the vertical, including guying strategies, material selection from scrap pipe, and weatherproofing the relay assembly. It highlights the use of a common mode choke for the relay switching line, measuring approximately 5K ohms on both 160m and 80m, and details the L/C matching network's role in achieving a 50-ohm match at the end of a 300-foot RG-11 run. The author describes a precise VNA-based radial trimming procedure, achieving resonant values within a 3 KHz range.

The content emphasizes the practical application of theoretical antenna principles, particularly concerning the interaction between the vertical element, cap hats, and the matching network. It offers a candid assessment of component selection, such as using junkbox parts and acknowledging the need for future upgrades to static drain resistors. The article serves as a comprehensive case study for advanced antenna builders tackling multi-band vertical designs.