Ralph Hartley

(1889 – 1970)

No account of Colpitts's work would be complete without a mention of Ralph Hartley, who invented the complementary oscillator.

Hartley graduated from the University of Utah in 1909 to become a Rhodes Scholar 11 at Oxford, graduating with a BAin 1912 and a BSc in 1913. He joined the laboratories of Western Electric in September 1913 and was in charge of early development of radio receivers for Bell System's radio telephone tests of 1915. By then he must have met Colpitts who was in charge of research there. It was at this time of radio receiver design, in a period of rapid circuit development, that Hartley revealed the oscillator named after him on February 10, 1915.

During the First World War Hartley suggested that the human sense of direction is perceived by the phase difference between sound waves reaching the two ears, one set of waves having to travel further than the other. After the war his interests turned more towards voice and carrier transmission and telephone repeaters, first at Western Electric and then at Bell Telephone Labs.

Hartley is also remembered for his major contributions to Information Theory. He was the first to state the law named after him relating information to bandwidth and time: "The total amount of information which may be transmitted over a system is proportional to the product of the frequency range which it transmits by the time during which it is available for the transmission." This was first published in February 1926 although he had been working on it for several years.

A fuller account, "Transmissions of Information", was given at an international meeting in Italy in 1927 and further published in 1928. Hartley's work on Information Theory followed that of Nyquist and "provided the guiding rules for transmission engineers for 20 years" until the next major advance in 1948 when Claude Shannon included the effects of noise in the system.

In 1929, at the age of 40, illness forced Ralph Hartley to give up work and it was ten years before he could return, as a consultant on transmission problems. During the Second World War he worked on various projects, most notably on servo-mechanisms for radar and fire control systems.

He retired from Bell Laboratories in 1950, holding 72 patents, and lived with his wife at Summit, New Jersey. He died at the ripe old age12 of 81 on May 1, 1970.

Task I

Tell about Hartley’s contribution to Information Theory.

Task II

Explain Hartley’s law.

Task III

Speak on Hartley’s scientific interests and inventions.

HARRY NYQUIST

(1889 - 1976)

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