Crystal radio sets, c 1920s.
© Science Museum / Science & Society Picture Library
The crystal radio set was simple and cheap. It consisted basically of a tuned circuit and a crystal detector, and had no batteries, the power delivered to its headphones all coming from the transmitter. Most designs used a wire 'cat's whisker' touching a favourable spot on the crystal at just the right presure. The slightest vibration, such as slamming a nearby door, could lose the programme being listened to altogether until patient adjustment brought it back.