Crystal set radios

Commercial radio broadcasting began in the US in 1920. Commercially manufactured radio sets were expensive, and many people built "crystal sets" out of readily available materials.

A crystal set radio consists of a very simple coil and capacitor tuner, a rectifier and a set of headphones. In early homemade versions, the antenna served as the capacitive element, and people wound their own tuning coils. The crystal set required no power - the rectified signal from a sufficiently powerful AM transmitter could drive headphones at enough volume that you could hear it.

In early crystal sets the rectifier (or "detector") was a natural mineral crystal (commonly galena) with a thin wire called a "cat's whisker" which lightly touched the crystal, and actually formed a primitive semiconductor junction. This device was inherently unstable, and the operator had to continually adjust it to find a good spot on the crystal, and obtain the right touch with the wire. It took some practice to be able to do it consistently.

Thus, we have two skills - building the thing, and adjusting the cat's whisker to be able to use it.

If you wish to build a modern version, you will probably use a germanium diode instead of the crystal (around $0.20 each, but you'll probably have to buy a pack of them for a couple bucks). Of course, I suppose this is no longer a "crystal" set, but the name persists.

A (commercially made) crystal set from 1925:

http://earlywireless.com/gecophone_junior_picinfo.htm

A modern version with a coil wound on an oatmeal box, a variable capacitor and a germanium diode:

http://www.streettech.com/archives_DIY/crystalSet.html

• list other references about this skill here

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