Construction of a 5/8-Wavelength Vertical Antenna for 2 Meters
Building a 5/8-wave vertical for 2-meter FM with series inductor matching
Description
A 5/8-wavelength vertical antenna for 2-meter FM operation is detailed, focusing on eliminating loading coils by utilizing a series inductor to cancel capacitive reactance at the feed point, thereby presenting a 50-ohm impedance match. The design illustrates three basic configurations, including a method employing a short-circuited coaxial stub for inductance, as implemented by K4LPQ.
An alternative design is presented where the center conductor of the stub is extended one-quarter wavelength, creating a signal-frequency short and allowing for an insulated wire stub to develop the required series inductance. The article provides electrical theory and mechanical considerations for building the antenna, emphasizing the adjustment of stub length for proper impedance matching.
This technical documentation is intended for amateur radio operators interested in homebrewing VHF antennas, offering practical insights into impedance matching techniques for vertical radiators.