First, we must have an aerial wire which the waves can cross and make electricity go back and forth into our coil. Whatever aerial you use, wrap one end of it around Nail A that connects with the coil and razor blade.
The longer the aerial the better. That will make more electricity move into the coil. You can use the wire that still is left on the spool and let it dangle out of a window. Or, better yet, perhaps you can get fifty or a hundred feet of any kind of wire and string it from a window to a tree out in the yard.
We also must have a connection to something that goes into the ground. The best ground connection is a cold water pipe. Take another piece of wire, scrape off the cotton covering and wind it tightly around a pipe. Take the other end of this wire and wrap it around Nail B.
With the aerial and the ground connected, we are all ready to get a program! Remember, a foxhole radio is different from the average set. So do not expect to hear music and voices booming in right away.
Put on the earphones, and do not make any noise in the room where you have your set. With your finger move the pin very gently so that the little piece of lead goes across the razor blade. Try putting the tip of the lead where the manufacturer of the blade has put his name.
Suddenly you will hear very faint little crackly noises in your earphones. Be careful. A station may come in at any moment. Move the pin just a shade more. Listen! There is somebody talking. Don’t move the pin. If you do, you may lose the station. Listen again. Do you hear two voices? You should not be surprised. Remember, we learned that a coil all by itself sometimes will let two programs come in.
A foxhole radio is a lot of fun. But why does it work?
Well, we know the incoming waves send electricity back and forth in the coil. But we know we must fix this electricity so that its changes will go in only one direction into our earphones.
The safety razor blade and the piece of lead act like an electrical gate. The blade is made of steel and the pencil point is made of carbon. When the steel and carbon touch each other, they will let electricity go through in only one direction. Once the electricity gets through the razor blade and the safety pin, it goes into our earphones.