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How to Build an Antenna Tuner

For the apartment-dwelling amateur radio hobbyist, space becomes a crucial factor when erecting an antenna. Depending on the radio frequency, you may require an antenna that is hundreds of feet long. An antenna tuner can reduce the required length of your antenna by maintaining the electrical resonance that is necessary for your shortwave radio to receive clear signals. By balancing capacitance and inductance, the tuner creates the illusion of a much longer antenna. Build this antenna tuner for the 3 to 30 MHz range, and learn the basics of antenna theory.

Things You'll Need

Variable capacitor, 365 pf, air type
Magnet wire, 24-gauge, 35 feet
Electrical wire, 16-gauge, 1 foot long
Wire with alligator clips, 6 inches long
PVC pipe, 1-inch diameter, 3 inches long
Plywood board, 6 inches square, 1/2-inch thick
Power drill, 1/4-inch and 1/8-inch bits
2 machine screws, 1/4 inch by 1 inch
4 machine screw nuts, 1/4 inch
Soldering iron and solder
Wire strippers
Two-part epoxy
Sandpaper

Instructions

- 1
  Drill two 1/8-inch holes side-by-side, 1/4 inch from both ends of the PVC pipe. Thread the magnet wire through the holes of one end of the pipe. Wrap the magnet wire around the pipe 100 turns, twisting the wire every 10 turns into a loop. Thread the wire through the holes at the other end of the pipe to lock the wire in place.
- 2
  Epoxy the wire to the pipe where the wire comes out of the drill holes to permanently fasten the wire to the pipe. Make sure the wire is wrapped tightly around the pipe before using the epoxy.
- 3
  Sand the coating off of each wire loop to create 10 exposed wire taps along the length of the pipe. Clip the wire at each end of the pipe. Leave three feet of wire at one end, and clip the wire short at the other.
- 4
  Drill two, 1/4-inch holes in one corner of the board. Insert a machine screw through each hole with the threads sticking up. Fasten the screws with a nut.
- 5
  Epoxy the PVC pipe vertically to the corner of the board diagonally, opposite the two drill holes. Make sure the wire taps face in toward the center of the board. Connect the three feet of excess wire from the PVC pipe to the external antenna jack on your radio.
- 6
  Epoxy the variable capacitor to a remaining corner of the board with the shaft facing out.
- 7
  Cut the electrical wire in half, and strip 1/2 inch from the ends of both lengths of wire. Solder one wire end to the rear metal frame of the capacitor. Wrap the other end around one of the screws in the board. This screw will be the ground connector.
- 8
  Solder one end of the other length of wire to a solder tab on the side of the variable capacitor. Wrap the other end of the wire around the other screw. This screw will be the antenna connector.
- 9
  Connect your radio antenna to the antenna connector screw and tighten a second nut to fasten the wires in place. Connect a ground wire to the ground connector screw and tighten a second nut over these wires as well.
- 10
  Connect the antenna screw to a wire tap on the PVC pipe with the alligator clips. Tune your antenna by adjusting the capacitor and attaching the alligator clip to different wire taps.

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