Eight coherers in the style of Georg Graf von Arco

When it receives electromagnetic waves, the resistance of the metal chips in the coherer changes, but the sensitivity was too low for practical use. In 1902, Georg Graf von Arco improved it by making the chamber, filled with silver powder and silver faience light, pointed into a wedge shape. Manual rotation can change the conductivity and thus the sensitivity of the coherer without removing it. As a result, the receiver became practical to use.