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The graphite inside your pencil

The graphite inside your pencil

There’s nothing magic about a radio. You can build your own radio out of plain ordinary things you can get at the store. Here’s how. You’ll need a detector, to pick the audio frequencies out of a radio wave. You’ll need an earphone, to hear the radio with. And you’ll need an inductor and capacitor to be able to make a tuner that lets you hear your radio better.

First, you need to make something that will vibrate when radio waves hit it. Anything with a crystal structure will do, but we’ll use the graphite from the inside of a pencil. Split open a wooden pencil and take out a piece of the graphite about an inch long (or use graphite from a mechanical pencil).

Rusty razor blade

Rusty razor blade

To make a diode, you’ll need a rusty razor blade, your graphite crystal, a safety pin, and some tape. The rust is important. If you haven’t got a rusty razor blade, use another piece of rusty metal, or put salt and water on a razor blade and hold it in a flame until it turns blue and purple. Now tape your pencil lead to the sharp end of an open safety pin. Make sure the graphite is touching the pin.

Now you need to make a tuner, or a resonator. This throws away all the radio signals we don’t want and only keeps the radio signals from one station at a time. First build an inductor. Take an old shampoo bottle and wrap about 50 feet of thin copper wire around it, in a spiral all down the length of the bottle, so the bottle is completely covered in wire. You need about 200 turns around the bottle.

Leave wires trailing off at both ends. Scrape off the insulation coating on the wires along one side of the bottle, but leave the insulation on everywhere else. Lay a wire coat hanger so that it is touching the bare wires on your bottle. When the coat hanger touches at one end, you’ll be at the top of the radio dial, and when the coat hanger touches at the other end, you’ll be at the bottom of the radio dial.

Now make the capacitor. Take a sheet of waxed paper about 4×6 inches. On top of it put a sheet of aluminum foil. Let the foil stick out a little bit. Put another piece of waxed paper over the foil, and then another piece of foil over that. The second piece of foil should stick out the other end of the waxed paper. Now roll the whole thing up like a jelly roll. You can even fold it the other way to make it smaller, as long as the two pieces of foil don’t touch each other.

Soup can

Soup can for the headphones

Now you can make the earphones. You’ll need a steel can (a soup can is good), a nail, a small magnet like a fridge magnet, and a bunch of thin copper wire. (Or you can make a magnet.) Wind a few hundred turns of wire around the nail. Let the magnet stick to the head of the nail. Attach the ends of the copper wire to your radio. Hold the can to your ear, and hold the magnet end of the nail very close to the bottom of the can.

Connect your diode to your inductor with a wire glued to the edge of the razor blade. Then connect your diode to your earphones with a wire taped to the other part of your safety pin.

Wrap about ten feet of copper wire around a metal fence post that goes down into the ground. This is the ground wire. Attach your diode to the other end of the ground wire – that’s your pencil lead with the safety pin attached. Take another piece of wire and attach it to the other end of the diode – the razor blade. That’s your antenna. Hang it in a tree, and make sure the bare end isn’t touching the ground. Now connect your tuner to the antenna. Connect the two ends of the earphone wires one on each side of the diode, one to your tuner and the other to your ground wire. Hold the can to your ear, and you may be able to pick up an AM radio station if there is a strong one in your area.

Bibliography and further reading about radios:


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