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 BA in 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 age¹²of 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)

American physicist, electrical and communications engineer, a prolific inventor who made fundamental theoretical and practical contributions to telecommunications. The Sweden years

Harry Nyquist's parents Lars Jonsson and Katarina Eriksdotter got married 1879. The year after they bought a farm in Tomthult. An interesting fact is that the family was baptists when the Swedish church is Lutheranian. The name Jonsson had to be changed because just hundred meters away there lived another Lars Jonsson and there was huge problem with the mail delivery. Therefore they agreed to change names, which not was a rare thing to do at this time. Harry's father changed the name to Nyquist.

Harry was the fourth child of eight and was born on 7 February 1889 in Nilsby, Sweden. The family was far from rich, but still the children were allowed to study six years in school and after that the continuing school with more concentrated education. Simultaneously Harry helped his father in his shoemaker's shop and the farm.

Harry's teacher Modén put a lot of confidence in Harry and Harry could even borrow books from his teacher (not common in those days). Modén wanted Harry to be a teacher. When Harry pointed out that his family was poor the teacher suggested that he should emigrate to America because the chances were bigger there. Two of Modén's sons had already done that. Harry was at that time 14 years old. The following years he worked at the construction of the sulphate factory in Deje in order to fulfil the demands on emigration and to get travel money: 10 dollars and a guarantee that he has a job in America. It took 4 years of hard work to fulfil the goal – to emigrate to America.