Superlight SOTA Vertical for 40-30-20m with Loading Coil

thingiverse

This is a lightweight vertical antenna designed for operation in mountainous terrain. The antenna features a loading coil that consists of two sections, with the upper section being tapped to provide separate connections for the 30 and 40 meter bands. The antenna is designed to be used with a 6m mast and requires a counterpoise that can be adjusted to tune the antenna. To assemble the antenna, start by winding the loading coil on a form, leaving enough room at each end for tapping. The tap should be located about one-third of the way down from the top of the coil. Connect the two ends of the coil to the SPDT switch, with the upper section connected to the left or right connector and the lower section connected to the middle connector. Next, connect the radiator wire to the end of the loading coil and attach it to the mast using rubber cable grommets. These grommets allow for a flexible connection between the wire and the mast, reducing wind-induced vibration. To tune the antenna, start by attaching it to a 6m mast with an initial radiator length of 5.17 m. Fold back the extra radiator wire and attach the enclosure/winder to the mast using two rubber bands. The enclosure should be positioned about 75-80 cm above ground level. Tune the antenna by winding up the counterpoise until it reaches resonance on the desired frequency band. A good starting point is to wind up about 5 m of counterpoise, making sure that it slopes down from the enclosure and does not touch the ground. Mark the tuned length of the counterpoise with a knot or rubber band. The antenna may require retuning for steeply sloped configurations, such as when used with a carbon-fiber mast. In this case, tie the hi-viz cord to the two unused holes in the enclosure and add a loop to the other end. Fix the loop with a peg, holding the winder/enclosure about 1m away from the base of the mast. The antenna is inspired by the original design by Joe Everhart, N2CX, and features several innovative components, including a tiny common-mode choke inspired by Richard Newstead's "pico balun." The idea to use a single SPDT on-off-on switch and rubber cable grommets is from Heinz Baertschi, HB9BCB.