How to Load a Coil on a Short Dipole Antenna

Written by adam quinn
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How to Load a Coil on a Short Dipole Antenna
A coil load placed at the centre of your dipole allows you to shorten your antenna and save space. (Jupiterimages/Comstock/Getty Images)

When a dipole's long antenna arms are shortened, its resonant properties change, diminishing performance. A small wire coil can be connected between the arms of the dipole, restoring the antenna's functionality. A short dipole with a loading coil will save space and retain its resonance with the radio frequencies you use to transmit. Build a 40-meter band, short dipole antenna, half the size of the standard.

Skill level:
Moderate

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Things you need

  • Electrical wire, 12-gauge, 60 feet long
  • PVC tube, 2 1/2 inch outer diameter, 6 inches long
  • Coaxial cable with connectors, 50-ohm, 10 feet long
  • Power drill and 1/8-inch bit
  • 2 wire caps, 12-gauge
  • 2 antenna-end insulators
  • Epoxy
  • Electrical tape
  • Wire-stripping tool
  • Utility knife
  • Fishing line

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Instructions

  1. 1

    Cut the electrical wire into one 20-foot length and two 19-foot lengths.

  2. 2

    Drill two 1/8-inch holes 1/2 inch from one end of the PVC tube. Thread the 20-foot length of wire through the holes. Wrap the wire 30 times tightly around the tube.

  3. 3

    Drill two 1/8-inch holes in the PVC tube after the 30th turn. Thread the remaining wire through the holes. Trim the excess wire on both ends short, allowing 2 inches of wire on either end to extend inside the PVC tube. Strip 1/2 inch of insulation from both ends.

  4. 4

    Wrap electrical tape around the PVC tube a few times to keep the wires in place. Apply a dab of epoxy over the holes to secure the wire ends to the tube.

  5. 5

    Find the 15th wire turn on the PVC tube. Using the utility knife, scrape off 1/4 inch of insulation from the wire. Count three wires right to the 18th turn, and remove 1/4 inch of insulation from this wire. These will be the feed line contacts.

  6. 6

    Cut a connector from one end of the coaxial cable. Remove 1 inch of insulation from this end. Slice down the side of the braided sheath and twist the braid into a wire. Strip 1/2 inch of plastic insulation from the inner copper wire.

  7. 7

    Solder the coaxial twisted braid to the 15th wire turn on the PVC tube. Solder the coaxial copper wire to the 18th turn. Wrap electrical tape around this connection to relieve the strain on the solder joints.

  8. 8

    Drill an 1/8-inch hole in both ends of the PVC tube. Thread a 19-foot wire through each end. Tie the wires to the tube, leaving 2 inches of excess at the end of the wires. Strip 1/2 inch of insulation from these wire ends. Using wire caps, fasten each of these ends to a wire end located inside the tube.

  9. 9

    Spread the antenna out, forming a T shape. Tie the free ends of each 19-foot wire to an insulator. Tie fishing line to the other end of each insulator. Hang the antenna taut using the fishing line.

  10. 10

    Connect the free end of the coaxial cable to your radio's external antenna jack.

Tips and warnings

  • Ground your radio to a cold water pipe to improve performance.

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