A Copper Tube J-pole
	by Ed Humphries - N5RCK
	edh@hpuerca.atl.hp.com

        The following is a description of a J-Pole antenna made from copper
        pipe. You can use 1/2 inch to 1 inch pipe (wall thickness will
        affect stiffness/stability AND price, but not performance). Larger
        diameter pipe increases bandwidth, but 1/2 inch is fine for amateur
        frequencies. Start with a 10 foot (standard) length of pipe, 1 90
        degree (right angle) fitting, 1 "tee" fitting, 2 end-caps, 2 hose
        clamps (worm-gear adjustable of the appropriate diameter), and your
        coax (end stripped, braid separated, center conducter stripped, and
        coax sealant to close opening in coax to keep water out). Use a tube
        cutter (for best/easiest results) and cut the 10 foot pipe according
        to the dimensions needed following the diagram below:
                     __
                        | <=endcap
                        |
                        |
                    5/8 | for 146 MHz
                        |
                        |
                   wave |
                        |
                        |
                        |
                     -- |   | <=endcap
                        |   | 1/4
                        |   | wave
                        |   |
    coax ctr conductor=>*   *<= coax shield
                        |   |
                 @ 5"-->|   |
                 tee =>  ---  <= elbow
                        |
                        | < "leftover" pipe
                        |

        For best general purpose use, the 5/8th wave version should be
        used. The dimensions to cut are: 66 1/2 inches (5/8 + 1/4 matching
        section), 19 inches (other half of 1/4 matching section), 3/4 inch
        (joins the tee and the elbow), and the "leftover" 33 3/4 inchs that
        forms the base. Use standard plumbing solder methods to join main
        section to base using the tee. Use the 3/4 inch piece and the elbow
        to attach the 19 inch piece. Be careful to keep pieces parallel.

        This will give you a center frequency of 146 MHz. Attach the coax
        as shown using the hose clamps. Adjust the swr at 146 MHz by sliding
        the connections up or down as needed -- you should be able to reach
        very close to 1:1 (best to do this in approximately where you intend
        to use the antenna - the base can be attached directly to a mast by
        two hose clamps). Try not to be standing right by the antenna!

        It has been noted that this design can lead to rf coupling onto the
        feedline. To avoid this, put a ferrite on the coax at the feedpoint,
        or use 3 turns (@1") of the coax taped together at the feedpoint.
 
        Other center freq dimensions: (adjust 5/8 section accordingly).
        144 =19.25 inches, 145 =19.12, 146 =19, 147 =18.86, 148 =18.73.