A redesign from the US Military Version .

The J-Pole is an older antenna design that’s been around a while, but not widely used or thought of these days.  It is a vertically polarized antenna with two elements: a ¾ wavelength radiator and a ¼ wavelength matching stub.  It operates as an end-fed half-wave antenna.  The ¼ wave stub cancels out ¼ wavelength of the ¾ wavelength radiator, thus leaving ½ wavelength to radiate.  The J-Pole does not require any ground radials and has a antenna gain of 2.4dB over isotropic (a half-wave dipole is 2.1dB gain over isotropic).  The formulas for the ¾ wave radiator and ¼ wave stub are:

L ¾ wave radiator = 8856 times velocity factor divided by frequency in MHz = length of ¾ radiator in inches
L ¼ wave stub = 2952 times velocity factor divided by frequency in MHz = length of ¼ wave stub in inches

The general design for a twin-lead Zepp is a 50Ω coax feedline, a λ/4 matching section, and a λ/2 radiating section. The feedline taps on near the bottom of the matching section.

A redesign from the US Military Version .

The general design for a twin-lead Zepp is a 50Ω coax feedline, a λ/4 matching section, and a λ/2 radiating section. The feedline taps on near the bottom of the matching section.

Built for the CB Band for the frequency values ​​from 27.0 Mhz to 27.9 Mhz this is a 3/4 wave antenna.

The below sweep is 26.95 MHz to 27.500 MHz ( USA ) spectrum but the antenna can be tuned for the complete CB band with a small adjustment. 

Hang and Play !