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1:1 Air-Core Balun

While analyzing several 1:1 balun designs to use on a dipole antenna for the 10 m and 20 m bands (2 half-wave dipoles coming down the same coaxial cable), I arrived at this simple project using an air core, covering 3–30 MHz and handling more than 100 W.

Trifilar coil wound on the 25 mm PVC pipe

Coil, 32 mm PVC pipe and end caps

Inside of the end cap with the hooks and connectors

End cap with the hook screws

Bottom cap with the UHF female connector

Inside of the pipe with the wiring soldered

Assembled and painted balun

Building the balun is quite simple: 9 trifilar turns of 14–16 AWG or 1.5 mm wire on a 25 mm PVC pipe. As a starting point I used the specifications from SM2YER, and the result came out very similar.

Winding diagram and schematic of the 1:1 balun (PY4ZBZ)

1:1 air-core balun diagram (SM2YER)

For the finish, a 32 mm diameter PVC pipe was used with a cap on each end. The UHF female connector was installed on the bottom end and, on the top, hook screws to hang the balun and tie off the antenna elements.

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