- The J Pole Antenna -
The J-pole antenna, also called the Zepp' antenna (short for Zeppelin), was first invented by the Germans for use in their lighter-than-air balloons.Trailed behind the airship, it consisted of a single element, one half wavelength long radiator with a quarter wave parallel feedline tuning stub. This was later modified into the J-pole configuration, which became popular with amateur radio operators because it is effective and relatively simple to build.
The J-pole antenna is an end-fed
omnidirectional dipole antenna that is matched to the feedline by a
quarter wave transmission line stub. Matching to the feed-line is achieved
by sliding the connection of the feedline back and forth along the stub
until a VSWR as close as possible to 1:1 is obtained. Because this is a
half-wave antenna, it will exhibit gain over a quarter-wave ground-plane
In this article you will find a basic drawing of a J Pole antenna and the lengths, spacings, and other details to build one for the 17, 15, 12, or 10 meter bands.
The J Pole antenna is a simple
antenna to build for most builders and requires little skill or tools to
make it work properly. Basically all that is really required is a good swr
meter designed for the bands you are building your J Pole antenna and some
basic soldering skills.
Below you will find the measurements for the 17 through the 10 meter band J Pole antenna. They can be built for the lower frequency bands like 20 meters but they become unusually tall for the average builder. An example would be about 49 feet tall for 14.300mHz! So we have not put those measurements on this page.
The lengths and measurements used in this article came from using the K4ABT calculator. See this page if you had rather use the calculator for other bands.
The formulas used for designing a J Pole antenna are as follows:
> 705 / frequency of use = feet
Usually higher swr readings than expected can be adjusted with the taps points either up or down.
An example: If you get 17.50 feet as your answer after using the formula, this is the same as 17 1/2 feet or 17 feet 6 inches. If the length was 17.69 you could round off to 17.70 feet. Then do the conversion from .70 to inches for a more useable number. On UHF (70cm) band, get the measurements as close to the calculated lengths as possible.
Use this handy conversion chart for help with conversions!
So lets get some J pole antenna measurements for the 17, 15, 12 and 10 meter bands below.
frequencies are at the top of each column below!
L = 1/2 wave section (longest)
S = 1/4 wave section (shortest)
Tap = Coax Feed Tap Starting Point (Adjust up or down equally for lowest swr)
Space = Spacing between longest and shortest element