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How To Make a Crystal Radio

Updated on February 25, 2014

Building Your Own Vintage Radio

Building a crystal radio is a fun project to build with your kids or even by yourself. Crystal radios are beauty in simplicity - they receive and play radio signals without an external power supply. They're one of the most simple electronic circuits you can build. The simplest designs only have 4 parts: an antenna, tuning coil, crystal detector (usually a diode), and an ear phone. More sophisticated versions might add extra coils, tuning capacitors, etc.

(Image: CODE 3 MEDIA AND MOTORSPORTS under Creative Commons)

Crystal Radio Schematic - You only need a few parts to build one...

Crystal radio schematic
Crystal radio schematic

Crystal Radio Parts

You only need a few parts to build a crystal radio. In fact, the simplest designs can be built with only four parts - a coil (inductor), diode (detector), earphones, and antenna. Adding a capacitor makes the design easier (unless you're building a kit), so figure on five parts. Still, that's not to bad - when you consider you're getting a complete working radio with only five parts (and no external power source) it's pretty amazing...

Crystal Radio Kits - For young kids, a kit is probably the best option...

A crystal radio is really easy to build, and it's not difficult to build one from scratch. If it's a project for a child though, or if you're just starting out (or just in a hurry) a kit is probably your best option. A kit is more convenient because it includes everything you need in one box. You don't have to worry about winding the coil, calculating inductance, or building the base. A kit is also more likely to work the first time (especially compared to designing your own radio) and is usually cheaper than buying the parts to build your radio from scratch. For these reasons, I recommend a crystal radio kit for your first attempt. Save the scratch building for your second radio...

The Antenna

Often overlooked, the antenna is one of the most important parts of a crystal radio...

The antenna is what pulls radio waves out of the air. On a crystal radio, the antenna also supplies all the electrical power needed to operate the circuit.For best reception and performance, the antenna should be at least 100 feet long for best reception. If you don't have that much room, don't worry - you can get OK reception with an antenna as short as 10 feet as long as you're near a transmitter putting out a strong signal.

The Coil

Your crystal radio coil must be properly tuned to receive radio broadcasts...

The coil an a crystal radio resonates at different frequencies along its length. The detector is attached to the coil, with the station being received depending on the point of contact on the coil.

The Detector

The detector is the heart of the radio...

A crystal radio uses a diode to convert the AM radio signal (which is alternating current) to a varying DC voltage. This process - called demodulation - is how the audio signal is extracted from the radio wave. Early crystal radio designs used a semiconductor crystal as the cathode with a wire contacting the crystal as an anode. The radio was tuned by moving the wire to various points on the crystal. This design is unstable though, and most modern designs use a germanium diode as the detector. On these designs, the radio is tuned either by moving the contact point for the detector to different points on the coil or by placing a variable capacitor between the coil and detector.

The headphone on a crystal radio takes the varying voltage from the detector and converts it to sound. Since a crystal radio has no amplifying circuit, the headphone must be very sensitive. Normal radio headphones won't work - you need a high impedance set designed for crystal radios.

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