How to build a high gain FM antenna

Written by adam quinn
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How to build a high gain FM antenna
A high gain diamond shaped antenna can receive distant FM stations. (Radio antenna in mountains image by Pavel Klimenko from Fotolia.com)

A high gain FM antenna can amplify reception of distant or weak radio signals. A diamond shape rhombic antenna is a type of high gain design that is accessible to both novice and experienced antenna builders. Traditionally the rhombic antenna required hundreds of feet of wire and an expanse of land for assembly. Build this smaller design that will fit in your home, and can be assembled using parts from your local electronic supply store.

Skill level:
Moderate

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Things you need

  • Twin-lead cable, 300 ohm, 50 feet long
  • 3 terminal strips, 2 position, dual row
  • 6 resistors, 1/4 watt, 220 ohm, 5 per cent% carbon film
  • 4 wire caps, 22 gauge
  • 12 nails or wood screws, flathead, 1/8 inch by 1 1/2 inches long
  • Drawing pins
  • Soldering iron and solder
  • Hammer or screw driver
  • Wire strippers
  • Utility knife

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Instructions

  1. 1

    Cut four 10-foot lengths of twin-lead cable and strip 1 1/2 inches of insulation from the ends.

  2. 2

    Connect two 10-foot lengths of twin-lead cable together using wire caps, being careful not to twist or cross the wire pairs. Repeat this with the other two 10-foot lengths. You now have two 20-foot cables connected at a node.

  3. 3

    Twist the twin-leads together on one end of each 20-foot cable, and then connect these twisted wires to the upper left and right screws of a terminal strip. This terminal strip, which forms the feedline corner of the diamond, should be oriented with the rows vertical.

  4. 4

    Place the two remaining terminal strips side by side with the rows oriented horizontally. These strips will form the termination corner of the diamond, diagonally opposite from the feedline terminal. Connect the free ends of each 20-foot cable to the outside, upper and lower screws of a separate terminal strip. Fit the four remaining screws with one end of a resistor.

  5. 5

    Spread out the antenna assembly to create a diamond, then fasten it to your ceiling. Nail or screw the terminal strips to the ceiling. Tack the cables to the ceiling, keeping them taut.

  6. 6

    Solder a third resistor horizontally, connecting the resistor pairs on adjacent terminal strips. This completes the antenna circuit.

Tips and warnings

  • Run the excess twin-lead cable from the single terminal strip to your FM receiver terminal inputs.
  • Attach a 300 ohm to 75 ohm matching transformer to the receiver end of the feedline if your FM receiver has a coaxial input.
  • Use a utility knife in conjunction with wire strippers to strip the ends of the twin-lead cables.
  • Depending on the size and shape of your ceiling, your diamond may be closer to a square shape.

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