J-pole antenna

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. This was later modified into the J-Pole configuration popular with amateur radio hobbyists.

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. Since this is a half-wave antenna, it will exhibit gain over a quarter-wave ground-plane antenna. The J-pole is somewhat sensitive to surrounding metal objects, and should have at least a quarter wavelength of free space around it.

A well known variation of the J-pole is the "Slim Jim", invented by Fred C. Judd (G2BCX).The name was derived from its slim construction and the J type matching stub (J Integrated Matching).

Both antennas should ideally be fed with balanced line, however a coax feed line may be used if a balun is added. Commonly, a choke balun is used, or an air transformer, using about five turns of coax. Typical construction materials include copper pipe, ladder line, or twin-lead. Coax can be used to match the J-Pole as somewhere between the closed circuit and open circuit of the stub an exact 50 ohm impedance match exists.

The J-pole antenna is popular with amateur radio operators, as it is effective and fairly simple to build.

External links

* [http://www.antennex.com/hws/ws0800/dbl_jp.htm J-Pole Double Header]
* [http://www.jpole-antenna.com/kb9vbr_jpole_plans.pdf 2 meter copper J-Pole construction plans]
* [http://www.cebik.com/content/a10/vhf/jp1.html Cebik: Some J-Poles That I Have Known] (Free registration required)
* [http://home.comcast.net/~buck0/ll_coolj.html 2 Meter half wave J-pole made from 450 ohm ladder line]
* [http://www.cebik.com/content/a10/vhf/sj.html Cebik: What is a Slim Jim?] (Free registration required)
* [http://www.hamuniverse.com/slimjim.html Slim Jim antenna project]

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Antenna (radio) — Whip antenna on car …   Wikipedia

  • Pole — may refer to:Cylindrical object*A solid cylindrical object with length greater than its diameter e.g: **Barber s pole, advertising a barber shop **Danish pole, a circus prop **Firemen s pole, a wooden pole or a metal tube or pipe installed… …   Wikipedia

  • pole — Synonyms and related words: China, Darkest Africa, God knows where, Greenland, Maypole, N pole, North Pole, Outer Mongolia, Pago Pago, Pillars of Hercules, S pole, Siberia, South Pole, Thule, Tierra del Fuego, Timbuktu, Ultima Thule, Yukon, acme …   Moby Thesaurus

  • antenna — an|ten|na [ænˈtenə] n ↑antenna, ↑wing [Date: 1600 1700; : Latin; Origin: pole holding up a sail ] 1.) plural antennae [ ni:] one of two long thin parts on an insect s head, that it uses to feel things 2.) plural antennas …   Dictionary of contemporary English

  • antenna — an|ten|na [ æn tenə ] noun count 1. ) (plural an|ten|nas or an|ten|nae) a wire or metal pole used for receiving or sending radio and television signals. British usually aerial 2. ) (plural an|ten|nae) one of the two long thin parts on an insect s …   Usage of the words and phrases in modern English

  • Microstrip antenna — In telecommunication, there are several types of microstrip antennas (also known as printed antennas) the most common of which is the microstrip patch antenna or patch antenna. A patch antenna is a narrowband, wide beam antenna fabricated by… …   Wikipedia

  • Dipole antenna — A schematic of a half wave dipole antenna connected to an unbalanced coaxial cable. Better practice is to connect the balanced dipole to the unbalanced line with a balun. A dipole antenna is a radio antenna that can be made of a simple wire, with …   Wikipedia

  • Rhombic antenna — signal gathering action compared to other end fire, backfire and traveling wave types. A rhombic antenna is a broadband directional antenna co invented by Edmond Bruce and Harald Friis,[1] mostly commonly used in HF (high frequency, also called… …   Wikipedia

  • Parabolic antenna — A parabolic satellite communications antenna at Erdfunkstelle Raisting, the biggest facility for satellite communication in the world, in Raisting, Bavaria, Germany. It has a Cassegrain type feed. A parabolic antenna is an antenna that uses a… …   Wikipedia

  • Loop antenna — A shortwave loop antenna A loop antenna is a radio antenna consisting of a loop (or loops) of wire, tubing, or other electrical conductor with its ends connected to a balanced transmission line. Within this physical description there are two very …   Wikipedia