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Nyquist, Harry

Nyquist, Harry

Nyquist, Harry

Swedish-born American Electrical Engineer
18891976

Harry Nyquist was an electrical engineer who was affiliated with AT&T from 1917 to 1954 as a researcher and inventor. His practical contributions to the computer science industry include improvements to long distance telephone circuits and picture transmission systems. His theoretical accomplishments in telecommunications laid the groundwork for T1 digital circuitry .

Nyquist was born on February 7, 1889, in Nilsby, Sweden. His family name was originally Jonsson. His parents, Lars and Kataerina Jonsson, had problems receiving their mail in Sweden because other men in the area were also named Lars Jonsson. A common local solution to such problems was for one family to change its name; thus, his family became the Nyquists. Although they were not wealthy and education was not free, the Nyquists managed to send all eight of their children to school for at least six years. Nyquist was a promising student who was encouraged to become a teacher. Since his family could not afford the extensive education necessary for a teaching degree, Nyquist, at age fourteen, decided to emigrate to the United States. For the next four years he worked at the construction site of a chemical factory in Sweden to qualify as an employable emigrant and to earn passage money.

In 1907 Nyquist arrived in the Unites States, and by 1912 he entered the University of North Dakota. He earned a bachelor of science degree in electrical engineering two years later, and his master's in 1915. Nyquist left North Dakota for Yale University to pursue a doctorate in physics, which he completed in 1917.

Upon graduation from Yale, Nyquist went to work for AT&T, where he remained until he retired in 1954. Nyquist started in the research department of AT&T. In the mid-1920s AT&T established Bell Laboratories as a research facility for studying theoretical and practical aspects of communication. Nyquist became a researcher with Bell Labs.

At that time Nyquist worked on telegraphy problems related to linear circuitscircuits that transmit electromagnetic signals in a fashion that allows the sending of multiple messages at different frequencies at the same time and allows two signals to travel in opposite directions at the same time. His observations were that the line speed of transmission was proportional to the width of the frequencies used. Nyquist published this theory in 1924 in the paper "Certain Factors Affecting Telegraph Speed." In his 1928 publication, "Certain Topics in Telegraph Transmission Theory," Nyquist presented the principles for converting analog signals, (i.e., voice or music) to digital signals, binary 0's and 1's, and back to analog, without loss of the signal's meaning.

The theorem that he offered was that a sample of twice the highest signal frequency rate captures the signal perfectly thereby making it possible to reconstruct the original signal. This work laid the foundation for many advances in telecommunications. Claude Shannon (19162001) incorporated this work in his development of information theory . It was not until the transistor was invented in 1947 that sampling, encoding, and transmitting of signals could be done fast enough to develop commercial communications systems that converted analog to digital signals. Today's T1 circuits, which carry digital signals converted from analog voice signals, are designed around the requirements of Nyquist's sampling theorem.

In addition, Nyquist expanded on J. B. Johnson's studies of thermal noise by providing a mathematical explanation which has become critically important for communications systems. His 1934 discovery of how to determine when negative feedback amplifiers are stable helped control artillery using electromechanical feedback systems during World War II.

Nyquist developed a method to transmit picturesa crude but working facsimile (fax) machinein which a photographic transparency was scanned, the scanned data was converted to electric signals in proportion to the intensity of shades and tones of the image, and these signals were sent over telephone lines to a photographic negative film. The film was developed using standard darkroom techniques. Today's fax machines work on the same principles.

Nyquist's thirty-seven-year career at Bell Laboratories included contributions to long distance telephone technology as well as the development of communication systems to transmit pictures. His accomplishments ranged from the theoretic to the technical and practical. In 1960 the Institute of Electrical and Electronics Engineers (IEEE) awarded Nyquist its medal of honor for significant contributions to the field of electronic engineering.

After retiring from Bell Laboratories in 1954, Nyquist served as a government consultant on military communications. He died on April 4, 1976, in Harlingen, Texas, at the age of eighty-seven.

see also Bandwidth; Shannon, Claude E.; Telecommunications.

Bertha Kugelman Morimoto

Internet Resources

"Harry Nyquist." <http://www.geocities.com/bioelectrochemistry/nyquist.htm>

Verstraete, A. A. "Nyquist's Theorem In-Depth." <http://www.smeal.psu.edu/misweb/datacomm/id/id_nyqui.html>

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