Slim Jim Antenna

Overview

Another variation of the J-Pole is commonly called a “slim jim” antenna and is normally made from 300Ω or 450Ω ladder line / twin feeder. These are popular as mobile antennas as they can be rolled up for easier transportation.

If the spacing cannot be set as per the calculator, this is OK. It will just affect the location of the feed point (which will probably need to be tweaked anyway).

It’s recommended that you start with the dimensions A and C being longer than specified by the formulas and cutting them back as needed to get the final impedance match (low SWR).

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.