J-Pole Antennas

Overview

J-Pole antennas are a type of omnidirectional vertical antenna that is popular for use on VHF/UHF frequencies. They use a radiator with a tuning stub. Unlike most antennas, these two parts are joined together at the bottom of the “J”, hence the name. The feed point is adjusted to get the proper SWR.

J-Pole antennas are commonly made from ½” copper pipe, but any conductive material can be used. The formulas assume using bare copper or aluminum as the construction material.

Construction

Notes:

• For all formulas, results are in inches and frequency (Freq) is in MHz.
• A choke should be placed just before the feed point, constructed from about 6 turns of coax with a 5” diameter. This prevents the coax from radiating as part of the antenna.