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How to Build a VHF/UHF J-Pole With Aluminum Tubing

J-pole antennas are popular amateur radio projects for the home builder. These antennas do not require a ground plane and offer broad bandwidth, so if the dimensions are carefully followed, the antenna will be resonant on the intended frequencies. A J-pole is a half-wave design using a tuned stub, and it will require a balun to match the antenna to the feed line. These instructions cover two separate antennas, not a dual band unit.

Things You'll Need

Aluminum tubing. 1/2-inch diameter
Stainless steel brush
Propane torch
Aluminum welding rod
Tape measure
Hacksaw
Round file

Instructions

- 1
  Measure the aluminum tubing carefully before cutting anything. The dimensions for a 2-meter J-pole are: 70 inches for the long side of the J, 19 inches for the short side of the J, and approximately 3 inches for the bottom. The bottom must be fitted, so it's slightly longer than necessary. For a 70 cm J-pole, the dimensions are: 18 15/16 inches for the long section, 6 3/8 inches for the short section, and 5/8 inches for the bottom. Due to the short bottom section, it is possible to simply bend a piece of aluminum rod to fashion a UHF antenna.
- 2
  Cut the lower section to length, then use the round file to "fish mouth" the end. File the tubing end so it fits tightly against the vertical tubes. When it's finished, the VHF vertical tubes should be 3 inches apart between their centers. The UHF bottom section must be formed to set the verticals 5/8 inches apart between their walls, not their centers.
- 3
  Attach the short lower section of the VHF antenna 58 inches from one end of the tubing. The other 12-inch section will be used to mount the antenna. Clean the tubing thoroughly with the stainless steel brush to remove any oxides. Place the tubing on top of a non-flammable work surface. A large piece of aluminum or steel is a good choice because it wills serve as a heat sink. Heat the joint with the propane torch and rub the aluminum welding rod into the joint. Do not apply heat directly to the rod. Attach the short vertical in the same manner.
- 4
  Attach the vertical UHF members to the bottom tube with the propane torch and aluminum welding rod. Unlike the larger VHF antenna, the smaller UHF antenna can be supported by a piece of PVC tubing or a painted dowel rod. Simply attach it to the longer vertical tube with a pair of zip ties.
- 5
  Drill holes for the feed points on each vertical tube. The VHF feed point is 2 3/4 inches above the bottom tube. The UHF antenna feed point is 5/8 inch above the bottom member. Use stainless steel screws and nuts to attach the feed line. The coaxial shield goes to the stub and the center conductor attaches to the long vertical.

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