Crystal Radio
Crystal Radio Science Kit
Collect electromagnetic waves that radio stations broadcast and convert them to electricity. Then transmit it to an earphone and listen to the radio.
A crystal radio does not need a battery. Electromagnetic waves from the air provide enough energy for the radio to work.
General Instructions:
The main components of a crystal radio are a coil of wire that you will make, a diode, an earphone and some wires. These materials can be purchased in pieces from a local electronic store or as a kit from this site.
The first step in making the radio is winding the tuning coil. This is best done with two people. One person should hold the paper roll and the other the spool of wire. Poke a small hole about a 1/2" from each end of the paper roll. Take the end of the wire from the wire spool and thread it through the hole. Pull the wire through so that it is about a foot long. Put a narrow strip of transparent tape around the end of the tube to keep the wire from slipping out during winding.
Now, begin winding the coil. When winding the coil, do not overlap the turns, they should lie adjacent to each other. When you are close to reaching the second hole on the other side of the roll, unwind an additional foot of wire and cut it off near the spool. Thread the end of the wire through the hole as before and apply a strip of tape.
One end of the coil will be attached to the antenna that can be any long wire. The other end goes to the ground. In other words you can connect it to any metal pipe or door or wire that is grounded.
The earphone also has 2 wires. One goes to the ground and the other will be connected to a diode.
The other end of diode will touch some place of the coil and depending on the spot that it touches the coil, you can be tuned on different radio stations.
Material needed (Included in the kit):
- Paper roll (as coil tube)
- Spool of insulated wire
- Germanium diode
- Screw, washer, and nut
- Tuner rod (or copper strip)
- Some wires
- Piece of sandpaper
- Plastic, wood or cardboard base
Additional Materials Required:
If you purchase a kit, you will not need any additional material. If you buy parts in pieces additional material required for your crystal radio are:
- Push-pins
- Clear adhesive tape
Opportunities for Science Fair Projects
Making a crystal radio is a good experimental project. If you want to do some more research, design experiments to answer the following questions. Prior to performing experiment, suggest a write down a hypothesis as the answer to your question.
- What is the effect of antenna on the performance of a radio?
- What shape, size and height antenna offers the optimum performance?
- What is the effect of ground wire in a crystal radio?
- Why is it called a crystal radio?
Crystal Radio Demonstration Video
Frequently Asked Questions
Why doesn't a crystal radio need batteries?
Crystal radios are powered entirely by the electromagnetic energy broadcast by radio stations. The radio waves induce a small current in the antenna, which is then detected by the crystal detector (diode) and converted to audio signals strong enough to drive high-impedance earphones.
What type of radio stations can I receive with a crystal radio?
Crystal radios work best with strong local AM (amplitude modulation) radio stations. They cannot receive FM stations because FM requires more complex circuitry. The stronger the station signal and the closer you are to the transmitter, the better the reception.
How important is the antenna and ground connection?
Both are crucial for good performance. The antenna should be as long and high as possible (50+ feet ideal). The ground connection should be to a good earth ground like a water pipe, ground rod, or electrical ground. Poor antenna or ground connections will result in weak or no reception.
Why is it called a "crystal" radio?
Early radio detectors used natural mineral crystals like galena (lead sulfide) with a fine wire "cat's whisker" touching the crystal surface to detect radio signals. Modern crystal radios use semiconductor diodes (usually germanium) which perform the same function more reliably.