J-Pole Antenna (Homebrew / Commercial)
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| Frequency | 144-148 MHz (typical 2m; scalable) |
| Bands | 2m (standard, monoband design; commercial dual-band versions exist) |
| Modes | FM, SSB, CW, digital |
| Connector | SO-239 |
| Year | 1940 |
| feedpoint | SO-239 |
The simplest effective VHF base antenna. A half-wave radiator fed through a quarter-wave matching stub. No ground plane required. Built from copper pipe, aluminum tubing, or twin-lead. The J-pole is the antenna every ham builds at least once because it works and costs almost nothing. Commercial versions from Ed Fong and others add dual-band capability.
The matching stub radiates if not properly configured. Gain is modest. Bandwidth is adequate but not generous. Copper pipe versions are heavy. Twin-lead versions are fragile. The feedpoint impedance is sensitive to nearby objects.
The VHF antenna everyone builds. The J-pole is to VHF what the dipole is to HF: the fundamental antenna that every operator should build at least once. A copper pipe J-pole in the attic outperforms any rubber duck antenna by an embarrassing margin.
The J-pole is one of the most popular homebrew VHF/UHF antennas in amateur radio, an end-fed half-wave vertical with a built-in quarter-wave matching stub that, together, form the shape of the letter J. That matching stub is the clever part: it transforms the very high impedance at the end of a half-wave radiator down to 50 ohms, so the antenna feeds directly with coax and needs no separate matching network or radials.
Most commonly built for the 2-meter band (and often dual-band for 70 centimeters), it is cheap and easy to make from copper pipe or twin-lead, which is why it is a perennial first-build project. As an end-fed half-wave vertical it offers a small amount of gain over a quarter-wave ground-plane and an omnidirectional pattern, making it a solid, no-fuss base or portable antenna for working local repeaters and simplex.
It is a timeless do-it-yourself design. Its flexible, foldable cousin the Slim Jim is a refinement of the same idea, and for a commercial base vertical the Diamond X50A covers the same job.