Ladder line or twin-lead cable is frequently used for antenna applications. The twin-lead design balances the electrical flow across the feed line, minimising impedance mismatch between the antenna and the radio. You can build a ladder line dipole antenna for the FM radio band, which will provide electrically balanced reception to your FM stereo receiver and minimise signal loss.
- Skill level:
- Moderately Easy
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Things you need
- Twin-lead cable, 300-ohm, 12 feet
- Wire-stripping tool
- Utility knife
- Soldering iron and solder
- Wood dowel, 1/4-inch diameter, 6 feet
- 2 short lengths of twine
Plug in the soldering iron and allow it to heat up. Clean the tip with a rag.
Measure and cut a 57 inch length of 1/16-inch twin-lead cable. Remove 1/2 inch of insulation from both ends. Cut through the centre ribbon between the wires, then strip the insulation from the wires with the wire-stripper. Twist the wire pairs together at both ends. Secure the connections by heating the wires with the soldering iron, pressing the solder against the wires until it melts. Allow the solder to cool. This will be the horizontal bar of the T-shaped dipole antenna.
Find the midpoint of the horizontal twin-lead cable, and cut the wire on one side of the cable at this point. Strip 1/2 inch of insulation from the wire on either side of the cut. This will be the feed line connection point.
Strip 1/2 inch from both ends of the excess length of twin-lead cable. Solder the wires at one end of this cable to the exposed wire ends at the midpoint of the horizontal twin lead.
Cut a hole in the insulation at both ends of the horizontal twin-lead cable. Tie a loop of twine through the holes. Hang the antenna by the twine.
Connect the free end of the vertical twin-lead to the external antenna jack on your FM receiver.
Tips and warnings
- A soldering iron can become very hot. Take care when soldering to avoid burns.
- Solder contains lead. Solder in a well-ventilated area, and avoid inhaling fumes.
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