How to Build a Dual-Polarity FM Transmitter Antenna

Written by adam quinn
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How to Build a Dual-Polarity FM Transmitter Antenna
Boost your FM transmitter's efficiency with a homemade dipole antenna. (BananaStock/BananaStock/Getty Images)

A dual-polarity antenna can boost your FM transmitter's signal. A folded dipole transmits radio signals in two directions, perpendicular to the antenna. This dual-polarity or dipole-radiation pattern concentrates the signal, which improves antenna gain. The folded dipole electrically balances the antenna to the transmitter, optimising transmission power, while remaining compliant with FCC transmission distance, which is 250 to 500 feet.

Skill level:
Moderately Easy

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Things you need

  • Speaker wire, 18-gauge, 12 feet long
  • Wire-stripping tool
  • Utility knife
  • Permanent marker
  • Electrical tape
  • Wire cap
  • Wood dowel, 1/8 inch thick, 57 inches long
  • Small piece of twine

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Instructions

  1. 1

    Separate 5 feet of speaker wire, leaving the excess intact. Remove 1/2 inch of insulation from the separated wire ends. Connect these ends with a wire cap.

  2. 2

    Measure and mark 28-1/2 inches along each wire, starting from the wire cap. At each mark bend the wire in half, and secure the bend by wrapping electrical tape around the folded wires. Lay the wires out in a T shape. The folded wire ends should form the left and right ends of the horizontal bar.

  3. 3

    Pinch the speaker wires together at the separation point to eliminate the slack in the lower wires of the horizontal arms of the T. Take up the slack until the separation point is touching the wire capped centre of the T. Wrap electrical tape around the wires at the separation point to keep the wires taut, and to avoid further separation.

  4. 4

    Wrap electrical tape around the wire pairs on either side of the wire caps, and along each arm of the T, to ensure the wires remain pressed against each other. Make sure either arm measures 28-1/2 inches.

  5. 5

    Mount and tape a dowel across the horizontal arms of the T to stabilise the antenna. Tie a piece of twine at either end of the dowel. Hang the antenna from the twine.

  6. 6

    Remove 1/2 inch of insulation from the free end of the speaker wire. Connect these ends to the external antenna jack of your FM transmitter.

Tips and warnings

  • Use an antenna tuner between the antenna and transmitter to improve transmission quality.

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