Hobbies And Interests
Things You'll Need
Instructions
Cut approximately 5 feet of twin lead. Strip half an inch of insulation from one end. Twist the wires together to form the bottom of the J. Solder the joined wires and clean the connection with alcohol. Carefully measure 1 1/4 inches above the soldered wires and strip 1/4 inch from both sides of the twin lead. Do not nick or cut these wires as they are the connections to coaxial cable.
Strip the insulation from the end of the coaxial cable opposite the BNC connector. Solder the center conductor to the radiator, which is the long side of the J. Solder the braid to the shorter tuning stub. Clean the connections with alcohol, then cover the joined wires with silicone sealant. Form a balun in the coax by looping four or five turns into a coil 1 to 2 inches in diameter. Secure the coils with zip ties.
Cut the twin lead to 51 1/2 inches if using twin lead with a velocity factor of 0.85. Alternatively, cut the lead to 50 3/4 inches if it has a velocity factor of 0.83. If the velocity factor is unknown, choose the longer measurement since the antenna will be cut for tuning later.
Form the tuning stub by measuring 16 3/4 inches above the bottom of the J. Do not take the measurement from the coaxial connection point. Remove 1/4 inch of insulation and conductor to make the stub. The remaining wire above the 1/4-inch gap will not have any effect on antenna operation.
Tune the antenna by trimming away small lengths of both the radiator and tuning stub. Connect the voltage standing wave ratio meter between the transmitter and the antenna. Select a frequency in the center of the 2-meter band. Key the transmitter and observe the meter. Trim small increments from both the radiator and stub in a 3:1 ratio. For example, if you cut 1/8 inches from the stub, cut 3/8 inches from the radiator until you achieve the lowest VSWR.