Stone Vintage Radio Museum - Antique Radios, Wireless, Crystal Sets, Tubes, and Valves

The coherer was the first detector that Marconi used. It was on of the detectors that were used for the transatlantic broadcasts in 1901. This is an original Marconi coherer attached to an ivory handle. Most of the first radio signals received by Marconi and other early experimenters in radio used a coherer as the detector. The coherer presents a large resistance to the passage of electric current through loose metal filings in the glass tube. The resistance decreases when a radio frequency current is received; when radio frequency signals are present the filings cling together - cohere - and allow a current to pass. This current actuated a telegraph sounder or could be heard in headphones. A problem of the coherer was that the filings continued to cling together after the radio signal ceased. Tappers, like on an electric doorbell, relaxed the metal filings so that another signal could be received.

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