How did the coherer help Guglielmo Marconi receive radio signals?

Guglielmo Marconi utilized the coherer—a device invented by Edouard Branly—to detect radio signals over long distances, such as his 1901 transatlantic transmission.1

The coherer consisted of a tube filled with iron filings. When a radio-frequency voltage was applied to the ends of the tube, the filings coalesced, or "cohered," which significantly improved the device's electrical conductance. This change in state allowed current from an auxiliary power supply to flow through the tube, triggering a relay that reproduced the transmitted Morse code signals. To ensure the device could detect subsequent signals, the coherer had to be regularly tapped to separate the filings and reset them to their original state.21