Coherer

The coherer, also coherer of Engl. Called coherer, is the original design of an electrically insulating tube, usually glass, but also hard rubber / ebonite, which is partially filled with metal shavings. The tube is closed at both ends with electrodes through which the electromagnetic waves are to be displayed supplied from the antenna. The coherer is used to detect electromagnetic waves in the frequency range of radio waves.

The coherer was developed in the 1880s by the Italian Temistocle Calzecchi - Onesti. His reports in the Italian magazine " Il Nuovo Cimento " found, however, in the professional world outside Italy little attention. Regardless developed in the 1890s Édouard Branly a relatively sensitive indicator of electromagnetic waves. Fritter are no longer used today and are to be designated as a historic unit.

Function

In the ground state with the metal shavings partially filled gap between the two electrodes is electrically virtually non-conductive. Meet the captured by the antenna electromagnetic waves on the coherer, so the connection is due to exceeding the fritting, also Frittschlussspannung, low resistance.

Since the coherers remains conductive after the arrival electromagnetic wave, it must be returned to its non-conductive state. It is sufficient to mechanically shake him, which is eg the telegraph by a clapper, clapper similar to an electric bell, causes. This bobbin is driven simultaneously with the Morse telegraph clerk by the relay and is functionally equivalent to Wagner's hammer. It is important that the clapper is arranged mechanically in the direction that is struck with the cancel signal by the clapper spring force on the coherer, and thus makes the coherer non-conductive. Only when again a signal arrives, move again clapper and possibly relay.

The combination of Fritter, clapper, telegraph relays and Morse recorder allowed in the early days of wireless technology to automatically record the then so-called " wireless telegrams ".

Mercury -based coherer

An extension, which avoided the usually complex mechanical structures for resetting to the non- conducting state, the mercury was based Coherer. It consists of a flat, filled with mercury shell. The mercury electrode is a dar. Above this is a thin layer of electrically non-conductive oil. In the oil layer, a thin metal plate is attached as a second electrical contact dipping from above. The metal plate is in this case adjusted such that in the resting state, the thin oil film between the mercury and the metal plate does not break down - so that the two terminals are electrically isolated from each other. Applies a high-frequency signal of sufficient voltage to the two electrodes, is produced between the terminals of an electrically conductive connection that is permeable to DC voltage. The connection breaks off again automatically when the high-frequency voltage is turned off.

Disadvantage of this design is the necessary precise adjustment of the metal plate and the position sensitivity of the arrangement, which is why the mercury- based coherer was not widespread.

Anti - coherer

" The Antikohärer consists of a thin metal foil, which is cut through by means of a zigzag-shaped fine scribe line so that the line of separation achieved in a small area as large as possible length. Joining the two halves of the film, bez. the terminals in such a manner that an element, a Vertikalgalvanometer Antikohärer and are connected in series into a circuit, the galvanometer will show a deflection when tender causes by breathing over a low moisture coating on the metal plate. Meeting now electric waves on the apparatus, the resistance of the Antikohärers suddenly increases, and the galvanometer returns to its zero position to give a rash after cessation of exposure. "