# Harry Nyquist

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**Harry Nyquist** (February 7, 1889 – April 4, 1976) was an important contributor to information theory.

He was born in Nilsby, Sweden. He emigrated to the USA in 1907 and entered the University of North Dakota in 1912. He received a Ph.D. in physics at Yale University in 1917. He worked at AT&T from 1917 to 1934, then moved to Bell Telephone Laboratories.

As an engineer at Bell Laboratories, he did important work on thermal noise ("Johnson–Nyquist noise") and the stability of feedback amplifiers.

His early theoretical work on determining the bandwidth requirements for transmitting information, as published in "Certain factors affecting telegraph speed" (*Bell System Technical Journal*, 3, 324–346, 1924), laid the foundations for later advances by Claude Shannon, which led to the development of information theory.

In 1927 Nyquist determined that the number of independent pulses that could be put through a telegraph channel per unit time is limited to twice the bandwidth of the channel. Nyquist published his results in the paper *Certain topics in Telegraph Transmission Theory* (1928). This rule is essentially a dual of what is now known as the Nyquist–Shannon sampling theorem.

Nyquist received IRE Medal of Honor in 1960 for "fundamental contributions to a quantitative understanding of thermal noise, data transmission and negative feedback."

He retired from Bell Labs in 1954.

Nyquist died in Harlingen, Texas on April 4, 1976.

## See alsoEdit

- Nyquist plot
- Nyquist–Shannon sampling theorem
- Nyquist frequency
- Nyquist stability criterion
- Nyquist ISI criterion

## External linksEdit

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