Home >> Science & Nature >> Science

How to Wind a Coil for a Crystal Radio

The earliest and simplest of radio receivers were crystal radios, which can still be used today and are easily constructed from scratch or from kits to receive AM radio broadcasts. All that is required to receive an AM signal is a wire antenna, earth ground, crystal detector or diode and earphones. No battery or power source is required. Add a tuning coil to these simple but versatile radio circuits to receive stations on several frequencies. Wind your own tuning coil from a wide variety of readily obtainable materials and capture multiple broadcast signals.

Things You'll Need

Stiff 2-inch diameter cardboard tube or PVC pipe
50 feet of thin varnished or enameled copper wire
6-inch piece of thick coat hanger wire
3 small pointed screws
Awl, punch or 1/8 in. drill
Needle nose pliers
Screwdriver
Sandpaper
Electrical tape

Instructions

- 1
  Obtain a six-inch long piece of stiff cardboard tube that you cannot crush easily when you squeeze it between your fingers. A cardboard juice can or a length of plastic PVC pipe will also work, but you will need to drill holes in PVC. Neither length nor diameter need to be precise, but about six inches long by two inches wide is typical.
- 2
  Take about 50 feet of thin enameled or varnished copper wire from an old power transformer or AC power adapter by carefully taking the transformer apart and unwinding the wire from inside. Use caution to avoid kinking the wire or scraping off any of the thin coating. Purchase a roll of wire from your radio and electronics supply store only if necessary.
- 3
  Punch or drill three 1/8-inch holes about one-half inch from each end of the six-inch tube for beginning and ending your coil windings. Two holes on each end are for securing the wire and the third hole on each end is to screw the finished coil in place on your crystal set.
- 4
  Insert about six inches of wire through two holes at one end of the tube and neatly wrap the circumference of the tube with electrical tape to hold the wire firmly in place.
- 5
  Wrap the wire firmly around the coil repeatedly for about 100 or so turns and insert the end of the wire through the two holes. Secure with electrical tape as on the other end.
- 6
  Connect your new coil to the radio. Mount the completed coil in place using the remaining two holes and the two pointed screws. Use sandpaper to sand off the enamel or varnish insulation in a line along the top of the coil. Use the needle nose pliers to put small loops in each end of a 6-inch piece of heavy coat hanger wire. Use one loop to screw the wire to the base near the center of the coil. Use the other loop as a handle to slide the wire back and forth across the sanded portion of the coil. This mechanical slide, when adjusted to various positions on the coil, will adjust the receiving frequency of your crystal radio set.

Science