Acoustic telegraphy
Encyclopedia
Acoustic telegraphy was also known as harmonic telegraphy. During the late 19th century, inventors developed methods of multiplexing
(transmitting more than one) telegraph messages simultaneously over a single telegraph wire
by using different audio frequencies
or channels
, 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
, 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
.
Some of Thomas Edison's devices used multiple synchronized tuning fork
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, 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.
All five of these Edison patents were assigned to Western Union Telegraph Company
of New York.
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
(transmitting more than one) telegraph messages simultaneously over a single telegraph wire
Electrical telegraph
An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via telecommunication lines or radio. The electromagnetic telegraph is a device for human-to-human transmission of coded text messages....
by using different audio frequencies
Audio frequency
An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...
or channels
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
, for each message. A telegrapher used a conventional Morse
Morse
Morse can refer to:* Morse code, a method of coding messages into long and short beeps-Places:Canada* Morse , Saskatchewan* Morse, Saskatchewan, a hamlet* Morse No...
key to tap out the message in Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
. The key pulses were transmitted as pulses of a specific audio frequency. At the receiving end a device tuned
Musical tuning
In music, there are two common meanings for tuning:* Tuning practice, the act of tuning an instrument or voice.* Tuning systems, the various systems of pitches used to tune an instrument, and their theoretical bases.-Tuning practice:...
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
Charles Bourseul
Charles Bourseul was a pioneer in development of the "make and break" telephone about 20 years before Bell made a practical telephone....
, Thomas Edison
Thomas Edison
Thomas Alva Edison was an American inventor and businessman. He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, practical electric light bulb. In addition, he created the world’s first industrial...
, Elisha Gray
Elisha Gray
Elisha Gray was an American electrical engineer who co-founded the Western Electric Manufacturing Company...
, and Alexander Graham Bell
Alexander Graham Bell
Alexander Graham Bell was an eminent scientist, inventor, engineer and innovator who is credited with inventing the first practical telephone....
. Their efforts to develop acoustic telegraphy, in order to reduce the cost of telegraph service, led to the invention of the telephone
Invention of the telephone
The invention of the telephone is the culmination of work done by many individuals, the history of which involves a collection of claims and counterclaims. The development of the modern telephone involved an array of lawsuits founded upon the patent claims of several individuals...
.
Some of Thomas Edison's devices used multiple synchronized tuning fork
Tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs formed from a U-shaped bar of elastic metal . It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone after waiting a...
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, 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 -- 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, 1880All five of these Edison patents were assigned to Western Union Telegraph Company
Western Union
The Western Union Company is a financial services and communications company based in the United States. Its North American headquarters is in Englewood, Colorado. Up until 2006, Western Union was the best-known U.S...
of New York.