Uploaded April 2021 | Updated September 2026, 3 hours ago
The coherer was a primitive form of radio signal detector
used in the first radio receivers during the wireless
telegraphy era at the beginning of the 20th century. The
device consists of a tube or capsule containing two
electrodes spaced a small distance apart with loose metal
filings in the space between. When a radio frequency signal
is applied to the device, the metal particles would cling
together or "cohere", reducing the initial high resistance of
the device, thereby allowing a much greater direct current
to flow through it.The coherer was a primitive form of radio signal detector
used in the first radio receivers during the wireless
telegraphy era at the beginning of the 20th century. The
device consists of a tube or capsule containing two
electrodes spaced a small distance apart with loose metal
filings in the space between. When a radio frequency signal
is applied to the device, the metal particles would cling
together or "cohere", reducing the initial high resistance of
the device, thereby allowing a much greater direct current
to flow through it. In a receiver, the current would activate a bell, or a Morse
paper tape recorder to make a record of the received
signal. The metal filings in the coherer remained conductive
after the signal (pulse) ended so that the coherer had to be
"decohered" by tapping it with a clapper actuated by an
electromagnet, each time a signal was received, thereby
restoring the coherer to its original state. Coherers
remained in widespread use until about 1907, when they
were replaced by more sensitive electrolytic and crystal
detectors.
The coherer was a primitive form of radio signal detector
used in the first radio receivers during the wireless
telegraphy era at the beginning of the 20th century. The
device consists of a tube or capsule containing two
electrodes spaced a small distance apart with loose metal
filings in the space between. When a radio frequency signal
is applied to the device, the metal particles would cling
together or "cohere", reducing the initial high resistance of
the device, thereby allowing a much greater direct current
to flow through it.The coherer was a primitive form of radio signal detector
used in the first radio receivers during the wireless
telegraphy era at the beginning of the 20th century. The
device consists of a tube or capsule containing two
electrodes spaced a small distance apart with loose metal
filings in the space between. When a radio frequency signal
is applied to the device, the metal particles would cling
together or "cohere", reducing the initial high resistance of
the device, thereby allowing a much greater direct current
to flow through it. In a receiver, the current would activate a bell, or a Morse
paper tape recorder to make a record of the received
signal. The metal filings in the coherer remained conductive
after the signal (pulse) ended so that the coherer had to be
"decohered" by tapping it with a clapper actuated by an
electromagnet, each time a signal was received, thereby
restoring the coherer to its original state. Coherers
remained in widespread use until about 1907, when they
were replaced by more sensitive electrolytic and crystal
detectors.
