the SIMPLE 2m Copper pipe "J"

by Dale “Kuby” Kubichek, N6JSX /8                                                                       03/2001

            Can you use a pipe cutter or a hack saw, can you solder – then here is how to build a SIMPLE ”J” antenna that will more than double your 2 meter (and even 440) performance!

            The "J" antenna goes back many years, long before I became a ham. There are a bunch of reasons why you're going to want to build one of these beauties:

                        “J” has the lowest angle of radiation,

                        “J” requires NO ground plane;

                        “J” is very easy and inexpensive to make;

                        “J” has great performance for mobile, marine, or base operations;

                        This “J” design can be used as a dual-band’er - 2m/440.

Technical:

            The basic "J" is reported to have >3dB of gain over a ¼ l ground plane antenna and 6dB over an isotropic (theoretical) antenna. The "J" can be made from almost any material: copper pipe, steel whips, and even 300 ohm TV twin-lead.

            Technically, the "J" antenna is an end-fed ½ l antenna that uses a ¼ l matching stub. Old-timers call it an "end-fed Zepp", bent 90°. In actuality, the conductor is ¾ l long and the matching section uses the bottom ¼ l. The matching stub creates the tuned ½ l length antenna.

            Due to the matching section acting as the matching transformer, the ½ l radiator sees the lower ¼ l matching section as an image of a false ground plane. In best terms, the "J" is a balanced ¼ l matching stub feeding an unbalanced ½ l load.

            The feed-lines to a "J" can be almost anything (ladder line to coax). However, in experimentation, I found RG-58/U coax to be best when used at odd ¼ wave multiples.

            A “J” is the best for mobile and marine application where you want the most distance across relatively flat ground/water. A 5/8 or ¼ l antennas have a higher angle of radiation and need to be centered on a good ground plane eliminating gutter or vehicle edge mounting to obtain optimal performance. A "J" requires NO additional ground plane.

            A “J” has an exceptionally low, to nearly flat, angle of radiation of about 0-2 degrees. The 5/8 l has about a 3-6 degree radiation angle and the highest radiation angle comes from the ¼ l that has about 4-10 degrees. These two antennas are usually better for mountain top (a few thousand feet elevated) repeater site use but will fall far short of a “J” in overall flat-land transmitting distance.

            The pictured “J” is at 60’ on top my tower in Manitowoc, WI. I can now hit repeaters across Lake Michigan, Milwaukee, or Upper Michigan that are well over 85 miles away.

Parts:

            The antenna pictured here is made from one 10’ piece of thick wall ¾” rigid copper pipe, one ¾” copper pipe “T”, one ¾” copper pipe 90° elbow, and three ¾” copper pipe caps, one SO-239 connector, and a 3” piece of 1/8” solid brass brazing rod (from a local welding supply company). These parts, plumbers flux, plumbers solder, and propane torch can be obtained at most hardware stores. Using copper pipe makes it easy to solder and snap to assemble. These materials will withstand a lot of abuse and weather. Total cost of this antenna was about $9.00.

I use ¾” thick wall copper pipe due to my ½” copper pipe “J” was bent in a 59 MPH wind gust last year. The ¾” thick wall is much stronger! Theoretically, the ¾” pipe should be slightly more broad banded but I’ve not measured any difference from ½” pipe “J”.

NOTE - about dimensions:

            I’ve seen numerous articles on “how-to” build a “J” antenna with various dimensions. Everyone seems to have the secret of the optimal “J” design dimensions. I’ve