Christian Jacobæus – the link system’s master

Ericrossbar, trade mark, 1960s

When Christian Jacobæus was employed by Ericsson in 1935, the crossbar system was about to achieve its breakthrough. Televerket, the Swedish PTT, had continued to develop the Betulander-Palmgren design from 1919 and to manufacture crossbar switching stations in its own workshops. Ericsson began manufacturing crossbar switches on a small scale in 1945. What was lacking, however, was a simple and reliable method for dimensioning crossbar switching systems. The person who solved this problem was Christian Jacobæus, after studying all the options offered by link systems.

Christian Jacobæus was born in Stockholm in 1911 and received his engineering degree in 1933. The results of his studies of telephone traffic were presented in 1950 in a doctoral thesis entitled "A Study on Congestion in Link Systems". The method was approximate but the results were sufficiently accurate for practical application. His method was quickly accepted as a standard by researchers and engineers all over the world. Jacobæus method was important for Ericsson, since the company was able to dimension its crossbar switching systems in a manner that was optimal for both customers and the manufacturer.

Jacobæus was appointed manager of Erisson's research department in 1950. From 1953 to 1976, he was technical director with responsibility for technical operations within Ericsson, and from 1963 to 1976, he served as Senior Vice President of Ericsson. He was the main author of "Evolution of the technology 1876-1976", the third part in the trilogy about Ericsson's that was published in connection with the company's centenary in 1976. In 1979 Christian Jacobæus became the first non-US citizen to be awarded one of the world's most prestigious prizes in the telecommunications industry, the Alexander Graham Bell Medal.

Christian Jacobæus died in 1988, at the age of 76.

Author: K V Tahranainen

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