Marconi Magnetic Detector
Marconi's magnetic detector, nicknamed the "Maggie," consists of a continuous iron band moving through a glass tube to which permanent magnets are attached. The tube is spirally wound with insulated copper wire; the wire terminals of this primary coil are connected between the antenna and a grounded connection. A secondary coil of insulated wire is wound on a spool which surrounds the primary; its wires are connected to headphones.
In the detector's operation, each section of the iron band is magnetized as it passes the permanent magnets and moves on. When each radio signal reaches the primary coil, the magnetism in the passing iron band changes. The changing magnetism induces a current in the secondary coil, resulting in a clicking sound in the earphones.
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