If you're a World War II buff and would like to build a wireless receiver like the ones from that era, a crystal radio design can get you started. The original wireless receivers were constructed using a galena crystal and a safety pin, and they used only electrical current from the radio signal itself. Crystal radio design evolved, with a germanium diode eventually substituted for the crystal. The spirit of wireless radio remains, however. A crystal diode radio can receive local AM stations without batteries or an electrical socket.
- Skill level:
- Moderately Challenging
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Things you need
- Plywood board, 6 inches by 12 inches, 1/2 inch thick
- Power drill and 1/8-inch bit
- 4 machine screws, 1/8 inch by 1 inch
- 8 machine screw nuts, 1/8 inch
- Oatmeal container, 1191gr.
- Magnet wire, 22-gauge, 60 feet long
- Adhesive tape
- Wood glue
- Wire strippers
- Germanium diode, 1n34
- Resistor, 47k
- Crystal piezoelectric earpiece, hi-impedance, with lead wires
- 2 pieces of electrical wire, 18-gauge, 6 inches long
- 2 alligator clips
Orient the plywood board with the long side horizontal towards you. Drill two 1/8-inch holes in the upper right corner of the board. Drill one 1/8-inch hole in the lower left and lower right corners. Insert machine screws through the bottom of the board, threads facing up. Fasten a nut to secure each screw.
Poke two holes in the side of the oatmeal container, 3 inches from the top. Thread the magnet wire through the holes. Wrap the wire 40 times tightly around the container, twisting the wire into a loop every 5 turns. The loops should stick out from the side of the container. Make sure to leave two feet of excess wire extending out the top holes.
Poke two holes in the side of the container after the fortieth turn. Thread the remaining wire through the holes, locking the wire in place. Place tape over the holes in the container to secure the wires in place. Trim the excess magnet wire, leaving one foot extending from the bottom holes.
Sand the insulation from the wire loops on the container, exposing the magnet wire.
Remove 1/2 inch of insulation from the upper and lower magnet wire ends. Remove 1/2 inch of insulation from both ends of the 6-inch wires.
Mount and glue the oatmeal container vertically to the upper left corner of the board. Twist the upper magnet wire end around the lower left screw, which will be the antenna screw. Twist the lower wire around the lower right screw, which will be the ground screw.
Twist the diode wire (indicated by a stripe on the diode housing) to a screw in the upper right corner.
Crimp an alligator clip to both ends of a 6-inch length of electrical wire. Clip one end to a loop on the oatmeal container and the other end to the free side of the diode.
Connect the remaining 6-inch wire between the lower right screw and the empty screw in the upper right corner. Connect the resistor across the two upper right screws.
Twist each end of the crystal earpiece around an upper right corner screw.
Attach two 6-inch wires to the antenna screw. Connect the ground screw to a cold water pipe using wire. Fasten a second nut to each screw, securing the wires in place.
Tune to various AM stations by connecting the alligator clip to different wire loops on the oatmeal container.
Tips and warnings
- Hang the antenna out a window or between posts in your yard for better reception.
- Do not hang the antenna near power lines.
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