Acoustic telegraphy (also known as harmonic telegraphy) was a name for various methods of
multiplexing (transmitting more than one)
telegraph
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
messages simultaneously over a single
telegraph wire by using different
audio frequencies
An audio frequency or audible frequency (AF) is a periodic function, periodic vibration whose frequency is human hearing range, audible to the average human. The International System of Units, SI unit of frequency is the hertz (Hz). It is the pr ...
or
channels
Channel, channels, channeling, etc., may refer to:
Geography
* Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water.
Australia
* Channel Country, region of outback Austral ...
for each message. A telegrapher used a conventional
Morse key to tap out the message in
Morse code. The key pulses were transmitted as pulses of a specific audio frequency. At the receiving end a device
tuned to the same frequency resonated to the pulses but not to others on the same wire.
Inventors who worked on the acoustic telegraph included
Charles Bourseul,
Thomas Edison
Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventi ...
,
Elisha Gray, and
Alexander Graham Bell. Their efforts to develop acoustic telegraphy, in order to reduce the cost of telegraph service, led to the
invention of the telephone
The invention of the telephone was the culmination of work done by more than one individual, and led to an array of lawsuits relating to the patent claims of several individuals and numerous companies.
Early development
The concept of th ...
.
[Standage, pp. 195–199]
Some of Thomas Edison's devices used multiple synchronized
tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs ( tines) formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it agains ...
s tuned to selected audio frequencies and which opened and closed electrical circuits at the selected audio frequencies. Acoustic telegraphy was similar in concept to present-day
FDMA
Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing ...
, or Frequency Division Multiple Access, used with radio frequencies.
The word ''acoustic'' comes from the Greek ''akoustikos'' meaning hearing, as with hearing of sound waves in air. Acoustic telegraphy devices were electromechanical and made musical or buzzing or humming sound waves in air for a few feet. But the primary function of these devices was not to generate sound waves, but rather to generate alternating electrical currents at selected audio frequencies in wires which transmitted telegraphic messages electrically over long distances.
Patents
* – ''Improvement in Transmitters and Receivers for Electric Telegraphs'' – Alexander Graham Bell, issued April 6, 1875
* – ''Electrical Telegraph for Transmitting Musical Tones'' – Elisha Gray, issued July 27, 1875
Reissue # 8559Jan. 28, 1879
* – ''Improvement In Electro-Harmonic Telegraphs'' – Elisha Gray, issued February 15, 1876
* – ''Acoustic Telegraph'' – Thomas Edison, issued October 10, 1876
* – ''Acoustic Electric Telegraphs'' – Thomas Edison, issued January 16, 1877
* – ''Acoustic Telegraphs'' – Thomas Edison, issued March 5, 1878
* – ''Circuits for Acoustic or Telephonic Telegraphs'' – Thomas Edison, issued April 30, 1878
* – ''Acoustic Telegraph'' – Thomas Edison, issued December 7, 1880
The five Edison patents were assigned to
Western Union Telegraph Company
The Western Union Company is an American multinational financial services company, headquartered in Denver, Colorado.
Founded in 1851 as the New York and Mississippi Valley Printing Telegraph Company in Rochester, New York, the company chang ...
of New York.
See also
*
Telegraph
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
*
Invention of the telephone
The invention of the telephone was the culmination of work done by more than one individual, and led to an array of lawsuits relating to the patent claims of several individuals and numerous companies.
Early development
The concept of th ...
References
;Notes
;Bibliography
* Standage, Tom, ''The Victorian Internet'',
Berkley Books, New York (Penguin), 1998,
* D. Robertson
''The Great Telephone Mystery'' IEEE Review, Feb. 2006, Volume: 52, Issue: 2, pp. 44– 48, , INSPEC Accession Number: 8770451, Current Version Published: 2006-02-27.
* Brooke Clarke
''Telephone Patents''
Telegraphy
Multiplexing
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