| The Coherer is a form of detector used in early continuous
wave radio receivers. It is a glass tube filled with sharply cut silver and
nickel shavings. Silver electrodes make contact with the shavings on both
ends. One electrode is connected to the antenna and the other to ground. A
series combination of a battery and a relay coil is also attached to the
When the oscillating signal from a spark transmitter is received, the shavings tend to cling to each other, reducing the resistance of the coherer. The battery supplies more current, and the relay is actuated, giving an audible click. The clapper of an electric bell mechanism then strikes the coherer, shaking up the filings and raising the resistance of the coherer to the original value.
This Coherer was given to the Greenslade Collection by Antoine DuBourg.
The bell mechanism to vibrate the filings in the coherer tube is concealed under the metal box on the right-hand side. On its top, stamped in tiny letters, is "L.E. Knott" of Boston. The workmanship, while good, is not up to production standards, suggesting that this might have been built to a special order by the firm in the early years of the twentieth century.
The coherer was invented by David Edward Hughes (1831-1900), who also invented one form of microphone.
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