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J-Pole

Vertical Antennas VHF Portable UHF 🔧 Buildable at home

An end-fed half-wave vertical matched by a quarter-wave parallel stub.

Band
VHF/UHF
Gain
~2-3 dBi
Polarization
Vertical

Photos

Schematic drawing of the J-Pole
Schematic drawing of the J-Pole (original).

Radiation / wave patterns

New to these diagrams? How to read a radiation pattern →

Radiation pattern of the J-Pole
Vertical, seen from above: omnidirectional. The half-wave radiator concentrates energy near the horizon.

How & why it works

The J-pole is an end-fed half-wave radiator with a quarter-wave parallel-line matching stub at the bottom that gives the structure its J shape. The shorted stub transforms the high end-feed impedance down to 50 ohms and the half-wave radiator needs no radials, so the whole antenna is a single mechanical piece that is easy to build from copper pipe or twin-lead. It produces an omnidirectional vertical pattern with a touch more gain than a quarter-wave ground plane.

Real-world uses

2 m / 70 cm amateur base and portable antennas, and emergency 'roll-up' antennas.

Make one at home

A practical starting point — always trim and check SWR for your exact frequency.

See the finished antenna pictured above ↑.

A J-pole is an end-fed half-wave with a quarter-wave matching stub — no radials needed. A 2 m copper-pipe J-pole is a rewarding weekend build.

You’ll need

  • 1/2-inch copper pipe + a tee and elbow, or 450-ohm ladder line for a ‘roll-up’ version
  • A coax connector and a hose clamp or two

Dimensions (2 m / 146 MHz example)

  • Long (half-wave) element: ~142 cm
  • Short (quarter-wave stub) element: ~48 cm
  • Spacing between them: ~5 cm
  • Feed tap: ~5 cm up from the bottom short. (Scale by frequency for other bands.)

Build

  1. Join the long and short elements at the bottom with the tee so they run parallel, shorted at the base.
  2. Attach coax centre to one side and braid to the other at the feed tap, a few cm up; slide the clamps to adjust.

Tune

Move the feed tap up/down a centimetre at a time for lowest SWR.

Safety

  • Keep antennas well clear of power lines — never put one where it could fall onto or contact mains wiring.
  • Don’t transmit while anyone is close to the antenna; mind RF-exposure limits and your local licensing rules.
  • Ground masts and use coax surge protection where appropriate.
  • Cutting/soldering: eye protection and a ventilated space.