The Physics
Factbook
An encyclopedia of scientific essays

The (Dysfunctional) Crystal Radio

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With a couple of household items and a crystal earplug an AM radio can be built (maybe)!

This is a great project for the Jr. scientist/physicist in your heart!

First acquire:

These are the schematics for the AM radio:

Now using the towel paper tube wrap many turns of wire making sure they do not cross. Next, scratch off a thin line of the enamel coating off of the coil. Now create the circuit part of the radio and connect the diode the earplug and the resistor in the fashion shown below. Make sure the circuit is grounded (the alligator clips may be used for this) and also the wire on the towel paper tube. Lastly the antenna is just wire that is connected to the top of the cylindrical tubes wire and extends in on direction above ground. Do not let the antenna touch anything metal.

The wire before the diode is placed against different points along the exposed wire on the tube. This will tune your radio. You should be able to hear something.

Unfortunately our group was unable to obtain the most crucial component of this experiment, the crystal earplug. So we used an amplifier and a speaker to attempt to hear our radio. We took apart some audio cables and we attached one where the earpiece used to be as shown below.

Next we plugged the plug into the aux input on a mini stereo system. The speaker was plugged into the right output. Now we checked to see if everything was properly grounded before plugging in the amplifier. We turned on the equipment and all we heard was static. Then we attempted to tune it by rubbing the wire before the diode against the exposed wire on the cylindrical tube. Upon contacting the wire with the cylindrical tube's wire we heard a staticky hum. We asked Mr. Elert whether the radio was working. He said it was but it was picking up interference from the laptops. We also learned that radio signals don't travel well or at all through reinforced concrete buildings like our beloved Midwood High School.

The moral of the story is: find the crystal earpiece!

Alexis Grisales, Matt Grabczynski, Manuel Caban, Willie Feng -- 2005