How to build a cigar box radio

Learn how radio works by building a foxhole radio in twenty minutes or less. Foxhole radios convert the energy in broadcast AM radio signals into sound that you can hear through a speaker or ear phone.

Building this simple AM radio used by the soldiers in World War II will help you gain an elementary understanding of radio and electronics. You can use the knowledge gained to help you build more complicated crystal radio projects.

Things you will need:

Phillips screwdriver
Cigar box:

Toilet tissue tube
Tape
Magnet wire, enamel coated
Crystal ear phone
Safety pin
Utility knife blade
Brass drawer knob, with screw
Jumbo paper clip
Screw on wire connectors, standard size
24 gauge insulated wire
Thumb tacks
Wire cutter/stripper
Rotary tool with drill bit
Sand paper
Standard screw on wire connectors

Step 1
Poke 2 holes side by side in each end the cardboard tube with the safety pin. Push one end of the magnet wire through one hole and back up through the second hole leaving about 6 inches of wire sticking out to connect to the antenna.
Step 2

Gently remove the enamel coating on the top of the coil and on the piece of wire sticking out from the coil with sand paper. This allows it to make good contact with the antenna, detector and tuning slide.

Step 3
Wrap 120 turns of magnet wire around the cardboard tube and cut the wire leaving about 3 inches. Push the wire down through the hoe in the end of the tube and back up through the other hole and secure the end to the tube with tape.
Step 4

Attach the coil to the top of the cigar box by pushing a thumb tack down through each end of the bottom of the cardboard coil form and into the top of the cigar box.

Step 5
Drill a hole in the top of the cigar box beside the coil using the rotary tool and insert the screw of a drawer pull through it. Wrap the end of the coil wire around the screw under the drawer knob, leaving the end of the coil wire exposed to attach it to the detector.
Step 6

Cut about 12 feet of insulated wire and strip the insulation off one end with the wire cutter/stripper tool. Wrap the stripped end of the antenna wire around the drawer knob screw and tighten the knob down on the screw with a screwdriver.

Step 1

Place the utility knife blade on top of the cigar box in front of the coil and push a thumb tack down onto it to hold it in place. The razor blade and safety pin will bet the detector diode that converts the AM radio waves into the electrical impulses the earphone changes into sound waves.

Step 2
Place the end of the coil wire on the edge of the blade and push a thumb tack down on it to hold it snugly against the blade. This connects the detector to the coil.

Step 3

Cut a 6 inch long piece of insulated wire. Strip off the insulation on both ends. This piece of wire will connect the detector to your earphone.

Step 4
Bend the head of the safety pin up sideways and position the pin on the cigar box so that the point of the pin is touching the safety knife blade.

Step 5

Place one end of the six inch wire on the safety pin head and stick a thumb tack down through the pin head to hold the pin and wire in place. Attach the other end of the wire to one of the wires coming from the earphone with a screw on wire connector.

The Tuner

Step 1

Open up a large paper clip and bend one end into a loop that will fit around a screw. Place it so that the end is touching the center of the coil and extending a little way past the coil. Wrap a piece of tape on the point of the paper clip and attach the clip to the cigar box with a ½ inch screw but do not tighten all the way.

Step 2

Cut a 6 inch piece of insulated wire to connect the tuner to the ground wire and the other side of the earphone. Strip both ends of the wire and wrap one end around the tuner screw. Tighten the tuner screw down with a screwdriver but leave it loose enough to move the tuner along the top of the coil to search for available AM stations.

Step 3

Cut a piece of insulated wire 3 feet long to use as a ground connection. Strip the insulation off both ends and connect the other side of the earphone wire, the wire from the tuner and one end of the ground wire together with a standard screw on wire connector.

Step 4
Stretch out the antenna wire and connect the end of the ground wire to a pipe or radiator. This will complete the circuit and you should be able to pick up nearby AM radio stations by moving the tuner along the top of the coil.

This kind of radio gets all its energy from the AM signal coming in over the antenna. The longer your antenna is the better you’ll be able to hear the radio.