A Copper Pipe Jpole for Two Meters

Notes: The J-pole antenna is a half wave radiator fed by an included 1/4 wave matching section. Thus it is about 3/4 wave tall at the operating frequency. A half wave radiator fed at one end presents a very high feedpoint impedance, at least several thousand ohms. The purpose of the 1/4 wave section at the bottom is to transform this very high impedance to a lower one that will match the 50 ohm feedline.

Because of the nature of the design, the very bottom of the J hook can be grounded. This means the entire antenna can be one continuous grounded metal piece. If mounted on top of a grounded metal pole it provides freedom from static charge accumulation and a measure of lightning protection.

The J-pole can be built for any frequency, but gets rather large below 10 meters. The match can be adjusted by moving the attachment point of the feedline on the bottom of the J. J-poles can also be built of flexible parallel wire like twin lead and several commercial roll up J-poles are available and work quite well as auxiliary antennas for hand held radios.

Building A 2-Meter Copper J-pole Antenna

By Rick Yost N4VQT 21-March-1991

MATERIALS REQUIRED

TOOLS REQUIRED


Assembly of the Antenna

1) PREPARATION OF COPPER PIPE:


Using the pipe cutter or hack saw, cut the 10' copper pipe into the following lengths:

The remainder of the copper pipe will be used as a mast mount. Sand the ends of all pipes to ensure a clean surface for soldering.

2) RADIAL ASSEMBLY:


Using the copper "T" connector fitting, connect the 3/4 wave pipe to the mast mount pipe so that both pipes are joined vertically. Insert the J connector pipe horizontally into the remaining T opening. Using the elbow, connect the 1/4 wave pipe to the J connector pipe thereby forming the J of the antenna. (see diagram below)

Lay the antenna flat on a bench with the connectors to be soldered hanging over the end of the bench so they can be heated without burning the bench. This will also ensure that 1/4 wave matching stub will be perfectly horizontal with the 3/4 wave pipe once the solder cools. Using the torch, heat the copper T fitting and when sufficiently hot, apply the electrical solder to the pipe where it joins the T. Do not apply heat directly to the pipe, just the connector. Repeat this on all connector joints. The end caps can be soldered on the tops of each radial after all other connections are cool.

3) PL-259 AND PL-258 COUPLER ASSEMBLY:


If you are using the RG-8X coax, install the reducer on the coax first. If using RG-8U or similar, the reducer is not required. Also, slide the outer portion of the PL-259 over the coax. Strip the coax end about 1 1/2 inches and peel back the shield of the coax to the insulating jacket. Strip the insulation off the center conductor about 1 inch. Tin the center conductor and wrap the shield around the remaining center conductor insulation.

PLEASE be certain not to short the center conductor to the shield. Connect the PL-259 using a twisting motion to the coax ensuring that the center conductor does not short to the shield. Apply solder to the tip of the PL-259 (coax center conductor) and the 4 holes (coax shield) in the body of the PL-259. The PL-258 coupler can then be connected to the PL-259. Using an Ohm meter, ensure that no short exists between the center pin and the outside of the PL-259 connector.

4) COAX CONNECTIONS:


Strip the black insulating jacket of the coax about 3 inches exposing the shield of the coax. Peel back the shield of the coax to the insulating jacket and twist the shield to form a tightly woven wire. Using a soldering iron, tin the twisted shield.

Scribe a mark on the 3/4 wave and the 1/4 wave pipes exactly 2 1/2 inches up from the inside portion of the J connector. (see diagram) Using the torch, apply heat to the under side of the pipe where you made the scribe. (that's the opposite side of the pipe). Apply a small bead of solder on the scribe points and ensure that the solder is adhering to the pipe.

After the beads of solder are somewhat cooled, grasp the coax with a pair of pliers and while heating the pipe, (again from the bottom) wait till the solder bead begins to liquify and apply the tinned shield portion of the coax to the 3/4 wave element. (Be sure to connect the shield of the coax to the 3/4 radial as close as you can to the insulating jacket. In other words, after the connection is cooled, you will be cutting off about 2 1/2 inches of unused shield.)

The tinned shield will also start to liquefy and the solder will join the shield to the radial. Remove the heat IMMEDIATELY after you see the solder on the shield liquefy with the solder on the radial. Allow the shield connection to cool to room temperature. Using an Ohm meter, check for any shorts between the center conductor and the shield and also check for continuity between the outside portion of the PL-259 and the antenna.

Next, the center conductor must be soldered to the 1/4 wave radial. Again, after the shield side has cooled, bend the center conductor over to the 1/4 wave radial and cut the center conductor insulation to allow the center conductor to be soldered to the antenna. Solder the center conductor using the same method as you did on the shield connection. Allow to cool to room temperature. Cut the excess shield and center conductor from the antenna. Using electrical tape, fasten the coax to the mast portion of the antenna just below the "J". (see diagram)

Your 1/2 wave copper J-Pole is now complete just add whatever length of coax you need and a 2-meter rig and your on the air!

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