The radio in diagram 1 uses a variable inductor (coil) for tuning. The radio in diagram 2 uses a variable capacitor for tuning. Both radios are otherwise the same. The coil consists of 110 turns of 28 gauge enameled magnet wire wound on a 1.5" form. (toilet paper tube is easiest to get, but you can use something like plastic or other non-conductive material- hollow is best. D1 is a common 1N34 germanium diode- this is the detector. The crystal earplug is not the same thing as one would commonly find at your electronics parts store. This is an high impedance earplug- very sensitive. You can get these from Crystal Radio Society or from Antique Electronic Supply. If you are going to build the radio in diagram 2 you will need the variable capacitor- If you cannot find one in an old junk radio then you can purchase one from either of the two suppliers above. The 47K resistor will load the circuit so that the sound from the earplug will not be distorted. If you are going to use a high impedance headset instead of the earplug then omit the resistor and instead use a .001 uf capacitor. For the variable inductor you will carefully remove the enamel insulation from the top of the coil with fine sandpaper (just until the bare copper is showing) Then a "wiper" can be fashioned from a large paper clip or stiff wire. By moving the "wiper" across the windings you will be electrically changing the inductance of the coil. This is how you will do your tuning. The antenna can be a length of any kind of wire 10' or longer. You should experiment with the antenna length. Ground the crystal radio to a cold water pipe or other known ground. Now, depending on where your local AM stations are located you should be able to hear one or more stations from the earplug. When listening at night you will usually be able hear many more stations as the radio waves skip off of the atmosphere. (sky wave propagation)
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