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Things You'll Need
Instructions
Measure the five copper pipe lengths that the J-pole antenna is composed of, using a tape measure. Cut the lengths from the copper pipe with a hacksaw. For the 146.0 MHz band cut three sections of copper pipe to the following lengths: 38.5 inches, 19.25 inches (x 2), 2.5 inches and 2 feet. For the 223.5 MHz band: 25.2 inches, 12.6 inches, 1.75 inches (x 2), and 2 feet. For the 440.0 MHz band: 12.8 inches, 6.4 inches (x 2), 1.25 inches and 2 feet.
Slide one end of the 2-foot section of copper pipe into one end of the T connector and solder it on using a torch and solder. This section will provide a way to mount the J-pole antenna to a tower or to the side of a building, as desired.
Insert one of the two medium-length pipe sections into the top of the T connector and solder it into place using a torch and solder. The straight vertical openings of the T connector should now have pipe lengths soldered into them, with the actual T portion pointing outward when the connected pipe lengths are held vertically.
Insert the shortest piece of the copper pipe into the final opening of the T connector so it is parallel to the ground when holding the straight section vertically. Solder the pieces together using a torch and solder.
Hold the entire assembly vertically with the shortest piece of copper pipe parallel to the ground. Solder an in-line copper pipe connector to the top section of copper pipe and solder a 90 degree elbow connector to the end of the section of pipe that is parallel to the ground. Rotate the elbow connector until the open end is pointing upward and also aligned parallel to the pipe that extends upward out of the T connector. Solder the 90-degree elbow using a torch and solder.
Insert the other medium-length section of copper pipe into the top opening of the 90 degree elbow connector and solder it using a torch and solder.
Insert the longest remaining section of copper pipe into the in-line connector but don't solder it yet.
Cut two 6-inch pieces ofsolid wire from a wire spool. Solder the end of one of the wires to the center "post" of the RG-58 connector on one end of the coaxial cable. Solder one end of the other wire to the outer jacket of same RG-58 connector. Connect the loose end of the wire that is connected to the "post" of the RG-58 connector to the copper pipe section that comes out of the top of the T connector and fasten the wire to that pipe securely with an adjustable hose clamp. Connect the loose end of the other wire to the pipe coming out of the top of the 90 degree elbow using the other hose clamp.. The wires should be connected 4 inches above the T and the elbow for the 146.0 MHz band, 2.5 inches for the 223.5 MHz band or 1.25 inches for the 440.0 MHz band.
Connect an SWR meter between the antenna and the transmitting radio you will be using with the antenna. Tune the radio to the center frequency of the band on which you will be using the antenna. Press the transmit key and observe how much power is reflected by the antenna back toward the radio. Your goal should be to lower the ratio to 1:1 (one unit out to one unit reflected). Loosen the hose clamps and move the wires up and down between transmissions until this ratio is as close to 1:1 as possible. If the SWR ratio is 1.5:1 or higher, proceed to the next step.
Tighten the hose clamps where the lowest possible SWR ratio is obtained and tune the radio upward and downward, performing a brief transmission after each frequency change. Continue doing this until you have reach the frequency at which you find the lowest possible SWR ratio. If the frequency is below the center frequency of the band, remove the top section (the one not soldered yet) and cut off 1/4 inch from one end. Insert back into the in-line pipe connector and check the SWR ratio at the center frequency again. Continue trimming 1/4-inch sections from that pipe until you have a 1:1 SWR ratio at that center frequency, or as close as possible to 1:1. A 1.2:1 radio is acceptable.
Solder the tuned top pipe to the in-line connector and the two coaxial cable wires using a torch and solder to finish assembly of the J-pole antenna. Remove the hose clamps after soldering the two wires. Cover the open ends of all copper pipe sections to prevent rain and snow water from entering the antenna and mount the finished antenna to the location of your choice.