page_title: Crystal radio
section_title: History
hierarchical_section_title: Crystal radio / History
caption_attribution_description: English: Photo of an American family in the 1920s listening to a crystal radio. From a 1922 advertisement for Freed-Eisemann radios in Radio World magazine. The small radio is on the table. Crystal sets work off the power received from radio waves, so they are not strong enough to power loudspeakers. Therefore the family members each wear earphones, the mother and father sharing a pair. Although this is obviously a professionally posed, promotional photo, it captures the excitement of the public at the first radio broadcasts, which were beginning about this time. Crystal sets like this were the most widely used type of radio until the 1920s, when they were slowly replaced by vacuum tube radios. Français&#160;: Photo d'une famille américaine dans les années 1920 à l'écoute d'une radio à cristal. D'une publicité 1922 pour-Eisemann radios Libéré en radio mondiale magazine. Cette photo de promotion capturant l'émotion du public à l'écoute de la radio à cette époque. Le petit poste de radio à cristal est sur ​​la table, fonctionnant sans alimentation électrique, d’une très haute fidélité sonore et d’une étonnante musicalité (comparé au récepteur moderne superhétérodyne). Mais, la limite de détection du signal radioélectrique est imposée par le niveau absolu des signaux reçus utile au fonctionnement de l’écouteur ou du casque (car les signaux reçus ne sont pas assez forts pour un haut-parleur de puissance. ). Car seul le signal radioélectrique de la station radio écoutée fait fonctionner le récepteur à cristal. Par conséquent, les membres de la famille ont des écouteurs. La radio à cristal comme tel était le type de radio le plus largement utilisé jusqu'à ce que les années 1920, quand ils ont été progressivement remplacés par des radios à tubes sous vide.
context_page_description: A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most important component, a crystal detector, originally made from a piece of crystalline mineral such as galena. This component is now called a diode.
  Crystal radios are the simplest type of radio receiver and can be made with a few inexpensive parts, such as a wire for an antenna, a coil of wire, a capacitor, a crystal detector, and earphones. However they are passive receivers, while other radios use an amplifier powered by current from a battery or wall outlet to make the radio signal louder. Thus, crystal sets produce rather weak sound and must be listened to with sensitive earphones, and can only receive stations within a limited range.
  The rectifying property of a contact between a mineral and a metal was discovered in 1874 by Karl Ferdinand Braun. Crystals were first used as a detector of radio waves in 1894 by Jagadish Chandra Bose, in his microwave optics experiments.
context_section_description: Crystal radio was invented by a long, partly obscure chain of discoveries in the late 19th century that gradually evolved into more and more practical radio receivers in the early 20th century. The earliest practical use of crystal radio was to receive Morse code radio signals transmitted from spark-gap transmitters by early amateur radio experimenters. As electronics evolved, the ability to send voice signals by radio caused a technological explosion around 1920 that evolved into today's radio broadcasting industry.
caption: A family listening to a crystal radio in the 1920s
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