How to make a FM Crystal radio
Try and assemble a "high-fidelity" FM crystal radio all by yourself! A Crystal radio can be prepared in a week's time with no prerequisites required and costs below $20.
How does a radio wave carry sounds such as voice or music to your radio receiver? The radio station broadcasts a carrier wave at the station's assigned frequency. The carrier wave is modulated (varied) in direct proportion to the signal (e.g., voice or music) that is to be transmitted.
The modulation can change either the amplitude or the frequency of the carrier wave. A radio receiver removes the carrier wave and restores the original signal.
Few ingredients required
L - 4 turns #18 copper or silver wire, 12mm inside diameter, tapped at 2.5 turns
Ant - 7 inches of #18 bare copper wire
C1 - 18 pf ceramic capacitor
C2 - 50 pf air variable capacitor
D - 1N34 diode or rock crystal
R - 150K resistor
The diode is tapped directly to the antenna. The vernier dial fits directly on the tuning capacitor. The antenna parallels the perimeter of the acrylic face plate. "Military style" #18 AWG wiring is used without any insulation. It is important to keep the components physically close together. The component specifications are the same as in circuit #2. The coil is silver rather than copper, but copper will do just as well. The coil was wrapped around a "magic marker", then slipped off and expanded. The wooden base is made from lacquered, polyurethane padouk (you can use any wood).
The FM radio works near the transmitter and at times you will have to move the set around to find a location for the best reception of signals.
A crystal radio is one that is not powered, except by the radio transmission itself and employs a crystal detector. So, it cannot have any batteries or AC power.
An FM crystal radio must be able to detect and receive FM signals well enough to be heard in earphones without any such extra power.
Via: Makezine
