How to Make a Crystal Radio

A crystal radio is the simplest form of a radio. It has simple, common components found at any electronics store and around the house and is easy to assemble. It has no power source and yet is sensitive to radio transmissions. Build your own crystal radio as a project for a science fair or a rainy Saturday afternoon.

Instructions

Difficulty: Moderately Challenging

Things You’ll Need:

• 1 16 oz. sturdy plastic bottle, 5 to 7 inches long
• 50 ft. 22-18 gauge enamel-coated magnet wire
• 1 germanium diode
• A telephone handset
• 1 Set of alligator jumpers
• 50 to 100 ft. stranded insulated wire (antenna, optional)

1. Use an icepick and make two holes 1/2 inch apart near the top of the bottle. Make two holes the same way near the bottom of the bottle. Try to make the holes only slightly larger than the wire.
2. Insert the wire and thread it through the bottom holes. Pull about 8 inches of wire out. Use the long end of the wire and wrap it around the bottle five times keeping each round close to the previous one. Stop and wrap the wire around a pencil to make a loop. Leave the pencil in place temporarily.
3. Wind the wire another five times and make another loop. Keep wrapping the bottle five turns at a time making a loop around the pencil every five turns until the bottle is completely wrapped in wire down to the second set of holes at the bottom. Trim the end of the wire to 8 inches and thread it through the two bottom holes.
4. Remove the pencil once the bottle is completely wrapped in wire. Use sandpaper to strip the insulation from the tips of the enameled wire and from the small loops or "taps" made around the pencil. Use a sharp knife to remove the insulation from vinyl-coated wire.
5. Solder the germanium diode to the bottom wire. Twist the wires and tape them, or use alligator jumpers instead of soldering, though soldering is best.
6. Cut the end off the telephone handset cord. Remove one of the modular connectors and find four wires inside. Solder either the yellow or black wire to the Germanium diode. Use the remaining wire (yellow or black) and solder it to the wire at the top of the bottle.
7. Clip an alligator jumper to one of the taps on the coil and clip the other end of the antenna. Join a second alligator clip to the wire at the top of the bottle (the ground wire.) Listen to different radio stations on the telephone handset by clipping the alligator to the other taps on the coil.

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