Fourth Graders Build Crystal Radios

Fourth Graders' Do-It-Yourself Crystal Radios
Building Instructions

In May 2000, as school was winding down, a class of eighteen fourth graders were winding up, literally! They wound their own electrical coils to build their own radios. I perceived the students to be totally enthusiastic about the prospects of such a fascinating homebrew project.

These radios have very few parts and consume no power. That's right: No batteries, no plugins, no solar power, no fuel cells, no wind power, no generators, ad infinitum. Crystal radios steal their power directly from the air waves using an antenna to grab the power out of the air. They are not loud, but they work.

The design we used is an adaptation of a 1932 design called the Mystery Radio, so called because it is a mystery that it works. The mystery is that one end of the antenna coil is not connected to anything (!), seemingly in violation of electrical rules, and the radio still works great. It is important to realize that the performance of this radio was considered state of the art in 1932. Enjoy the images.

Walking the Coil
The wire was tied to a chain link
fence. The students pulled it taut.
Then they just rolled the cardboard tube
coil form toward themselves while
gradually walking toward the fence.
The resulting coils were wound beautifully.

Punching Holes
The coils have two windings. This student
is using a pushpin to punch holes to secure
the wire for the second winding.
The Elmer's Glue is resting on the baseboard
that holds the radio parts. The circuit diagram is printed on the paper so the students
can see where the parts fit.
The Dr. Pepper can finds service
as the variable capacitor.

Finished Product
See what I mean about
the beautiful coil winding?
The Dr. Pepper can is surrounded
by a cylinder of paper which is faced
on the inside with an insulated strip
of aluminum foil. The foil forms one plate
of a capacitor, and the can itself forms another.
When you slide the paper and
foil strip up and down, you vary the
capacitance, which tunes the radio
to different stations. Excellent!

To see a more advanced crystal radio I built for a contest, CLICK HERE .

If you want to do more with crystal radios, here is one really good link: CLICK HERE.

E m a i l (click here, then click on link by the picture on following page)

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Counter added May 1, 2001

	Walking the Coil The wire was tied to a chain link fence. The students pulled it taut. Then they just rolled the cardboard tube coil form toward themselves while gradually walking toward the fence. The resulting coils were wound beautifully.
	Punching Holes The coils have two windings. This student is using a pushpin to punch holes to secure the wire for the second winding. The Elmer's Glue is resting on the baseboard that holds the radio parts. The circuit diagram is printed on the paper so the students can see where the parts fit. The Dr. Pepper can finds service as the variable capacitor.
	Finished Product See what I mean about the beautiful coil winding? The Dr. Pepper can is surrounded by a cylinder of paper which is faced on the inside with an insulated strip of aluminum foil. The foil forms one plate of a capacitor, and the can itself forms another. When you slide the paper and foil strip up and down, you vary the capacitance, which tunes the radio to different stations. Excellent!