“... with enough ingenuity, one could tickle the crystal with a cat's whisker and pick up anything"
Theodore H. White, journalist, historian, and author
Greenleaf Pickard (1877-1956) was a pioneer in the early days of wireless. He experimented with methods of receiving radio signals, using mineral crystals to filter out noise in the signal. After testing more than 30,000 combinations of materials, he finally patented his "crystal detector" in 1906. This featured a crystal of silicon that was later connected to the radio circuit via a fine, sharp piece of wire known as a cat's whisker.
A crystal set radio is the simplest form of radio as it needs no power source to receive signals. A typical set consists of an antenna, a detector, a tuner, and an audio output—normally an earpiece. The antenna can be any piece of wire or metal.
As radio waves pass through the antenna, tiny voltages are created from all radio stations broadcasting. The antenna is connected to a tuning circuit comprising a coil and a capacitor. The capacitance can be varied and, in conjunction with the coil, acts as a filter to allow only the voltages from certain stations to pass. The filtered signal is then passed on to the detector. The detector performs the demodulation of the signal, letting only the radio program pass through to the earpiece, where it can be enjoyed. The cat's whisker needed to be moved across the surface of the crystal to form the best contact and so allow the best clarity of sound.
Crystal sets were particularly popular in the early 1920s when radio broadcasting was beginning to take off but factory-made radios were still prohibitively expensive. At the time, instructions on how to make crystal sets out of household items such as cereal boxes and baseball bats were published.
