page_title: Radio receiver
section_title: Coherer receiver
hierarchical_section_title: Radio receiver / History / Spark era / Coherer receiver
caption_attribution_description: 日本語: 合資会社　平川研究所（HIRAKAWA-IT）より提供。 2007年11月22日、権利放棄されていることを直接確認。公開承諾。 平川研究所製作、検証用、銀-ニッケル復元コヒーラ。 2007年11月23日、デジタル修正版再提供。掲載変更依頼。 English: A Branly coherer, 1902, an early primitive radio wave detector invented by Edouard Branly in 1890 and used in the first radio receivers until about 1906. This version, developed by Guglielmo Marconi, consists of an evacuated glass tube with metal filings between two metal electrodes. Radio waves from the antenna, applied across the electrodes, cause the filings to cohere, reducing the resistance of the device. This turns on a DC circuit attached to the electrodes, powered by a battery, that makes a "click" sound in earphones or a mark on a paper tape, to record the Morse code signal. The slanted faces of the electrodes allowed the gap between them, and thus the sensitivity of the detector, to be adjusted by rotating the tube. Deutsch: Fritter, 1902. Ein früher, primitiver Radiowellenempfänger. 1890 von Edouard Branly erfunden. Wurde bis 1906 in den ersten Radio-Receivern verwendet. Diese Version, von Guglielmo Marconi entwickelt, besteht aus einer Vakuum-Glas-Röhre mit Metallspanfüllung zwischen zwei Metallelektroden. Radiowellen, welche von der Radioantenne an die Elektroden geleitet werden, richten die Metallspäne so aus, dass der Widerstand der elektrischen Verbindung sinkt. Dies aktiviert eine von einer Batterie getriebene, angeschlossene Gleichstromschaltung, die ein Click-Geräusch in einem Kopfhörer oder eine Markierung auf einem Papierstreifen erzeugt, um so das Morsesignal aufzuzeichnen. Durch die abgeschrägten Elektroden kann durch Rotation der Röhre die Lücke zwischen diesen, und damit die Empfindlichkeit des Empfängers, eingestellt werden. Français&#160;: Cohéreur (de Branly) 1902. Tube de verre dans lequel on fait le vide, contient entre deux tampons métalliques quelques fragments de limaille peu oxydable. La résistance du tube à limaille diminue brusquement dans de fortes proportions en présence d'une onde hertzienne le traversant, la limaille est cohérée. Ce détecteur d'ondes hertziennes a permis de réaliser les premières liaisons radios à grande distance en radiotélégraphie
context_page_description: In radio communications, a radio receiver, also known as a receiver, a wireless or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The receiver uses electronic filters to separate the desired radio frequency signal from all the other signals picked up by the antenna, an electronic amplifier to increase the power of the signal for further processing, and finally recovers the desired information through demodulation.
  Radio receivers are essential components of all systems that use radio. The information produced by the receiver may be in the form of sound, moving images, or digital data. A radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar type of radio receiver for most people is a broadcast radio receiver, which reproduces sound transmitted by radio broadcasting stations, historically the first mass-market radio application.
context_section_description: The first radio receivers invented by Marconi, Oliver Lodge and Alexander Popov in 1894-5 used a primitive radio wave detector called a coherer, invented in 1890 by Edouard Branly and improved by Lodge and Marconi.  The coherer was a glass tube with metal electrodes at each end, with loose metal powder between the electrodes.  It initially had a high resistance.  When a radio frequency voltage was applied to the electrodes, its resistance dropped and it conducted electricity. In the receiver the coherer was connected directly between the antenna and ground.  In addition to the antenna, the coherer was connected in a DC circuit with a battery and relay. When the incoming radio wave reduced the resistance of the coherer, the current from the battery flowed through it, turning on the relay to ring a bell or make a mark on a paper tape in a siphon recorder.   In order to restore the coherer to its previous nonconducting state to receive the next pulse of radio waves, it had to be tapped mechanically to disturb the metal particles.  This was done by a "decoherer", a clapper which struck the tube, operated by an electromagnet powered by the relay.
  The coherer is an obscure antique device, and even today there is some uncertainty about the exact physical mechanism by which the various types worked.   However it can be seen that it was essentially a bistable device, a radio-wave-operated switch, and so it did not have the ability to rectify the radio wave to demodulate the later amplitude modulated (AM) radio transmissions that carried sound.
  In a long series of experiments Marconi found that by using an elevated wire monopole antenna instead of Hertz's dipole antennas he could transmit longer distances, beyond the curve of the Earth, demonstrating that radio was not just a laboratory curiosity but a commercially viable communication method.  This culminated in his historic transatlantic wireless transmission on December 12, 1901 from Poldhu, Cornwall to St. John's, Newfoundland, a distance of  3500 km (2200 miles), which was received by a coherer.  However the usual range of coherer receivers even with the powerful transmitters of this era was limited to a few hundred miles.
  The coherer remained the dominant detector used in early radio receivers for about 10 years, until replaced by the crystal detector and electrolytic detector around 1907.  In spite of much development work, it was a very crude unsatisfactory device.  It was not very sensitive, and also responded to impulsive radio noise (RFI), such as nearby lights being switched on or off, as well as to the intended signal. Due to the cumbersome mechanical "tapping back" mechanism it was limited to a data rate of about 12-15 words per minute of Morse code, while a spark-gap transmitter could transmit Morse at up to 100 WPM with a paper tape machine.
caption: Coherer from 1904 as developed by Marconi.
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