Coherer detector of electromagnetic signal

, Roobert33 The coherer, invented by an Italian Calzecchi Onesti in 1884, is nothing more than a glass tube into which was inserted the metal filings extremely fine, usually made up of nickel and iron interposed between two electrodes metal plugs that also close the glass tube. The resistance of this filing between the electrodes under normal conditions is very high, then the electric conductivity is practically nothing; this resistance is lowered abruptly when the coherer is invested by an electromagnetic wave, and then in the circuit there is a considerable increase or a complete conductivity of the current that reveals the signal. Marconi used it to make the bell of his first radio receiver in 1894 To replicate: The distance between the two electrodes inside the tube should be more or less than 23 mm. When the filing of nickel is inside the tube, it should not be pressed, it needs to move