- The J Pole Antenna -
Design one for 17, 15, 12, or 10 Meters

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 antenna.

The J-pole antenna is somewhat sensitive to surrounding metal objects, and should have at least a quarter wavelength of free space around it. The J-Pole is very sensitive to conductive support structures and will achieve best performance with no electrical bonding between antenna conductors and the mounting structure. (This last sentence is debatable and ingnored by many builders).

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.

The J Pole antenna can be made from regular TV twinlead, 450 ohm ladder line, aluminum tubing, copper tubing or wire using spacers for support as needed. See links at bottom of this article for more info. It is a forgiving antenna on hf using the calculated measurements and tuning is usually easy for lowest swr due to the 1/4 wave matching stub and tap points that can be changed as needed and tuning is much easier on the hf bands. The J Pole becomes a bit more critical in the measurements and tuning on VHF and even more so on the UHF ham bands.

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:

Total length (1/2 wave element)                    >    705 / frequency of use = feet
Short length (1/4 wave element)                   >    234 / frequency of use = feet
Feed Tap Point up from bottom)                   >      23 / frequency of use = feet
Spacing between long and short sections   >      22 / frequency of use = feet

Notes and and construction info:

(These formulas work well up into the 2 meter band. But the lengths, diameter of the radiator and measurements get somewhat more critical on higher frequencies.)

{Note that by using these formulas, you uaually get some lengths that will have to be converted from decimal to inches, etc.} On the hf bands, these are not very critical but at the higher frequencies, some conversion may be needed.

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.

Design frequencies are at the top of each column below!
No need to use the formulas or the calculator. We have done them for you!

17 Meters 18.130MHz	15 Meters 21.375MHz	12 Meters 24.96MHz	10 Meters 28.400MHz
L = 38 feet 7/8 inches	L = 33 feet	L = 28 feet 3 inches	L = 24. feet
S = 13 feet rounded off	S = 11 feet	S = 9 feet 3/8 inches	S = 8 feet 1/4 inches
Tap = 15 1/4 inches	Tap = 1 foot	Tap = 11 inches	Tap = 9 feet 3/4 inches
Space = 14 1/2 inches	Space = 12 3/8 inches	Spacing = 10 1/2 inches	Spacing = 9 1/4 inches

(All numbers in chart above rounded off.)

Legend:
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