Otto Julius Zobel

Otto Julius Zobel
Born	(1887-10-20)October 20, 1887 Ripon, Wisconsin
Died	January 1970 (aged 82) Morristown, New Jersey
Residence	New Jersey
Nationality	American
Fields	Electrical engineering
Institutions	AT&T Co, Bell Labs
Alma mater	University of Wisconsin
Known for	Filters, equalisers and matching networks
Signature
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Zobel's signature in his draughtsmanlike hand as it appears on a patent application

Otto Julius Zobel (October 20, 1887 – January 1970) was an electrical engineer who worked for the American Telephone & Telegraph Company (AT&T) in the early part of the 20th century. Zobel's work on filter design was revolutionary and led, in conjunction with the work of John R. Carson, to significant commercial advances for AT&T in the field of frequency division multiplex (FDM) telephone transmissions.

Although much of Zobel's work has been superseded by more modern filter designs, it remains the basis of filter theory and his papers are still referenced today. Zobel invented the m-derived filter and the constant-resistance filter, which remains in use.

Zobel and Carson helped to establish the nature of noise in electric circuits, concluding that—contrary to mainstream belief—it is not even theoretically possible to filter out noise entirely and that noise will always be a limiting factor in what is possible to transmit. Thus, they anticipated the later work of Claude Shannon, who showed how the theoretical information rate of a channel is related to the noise of the channel.

Otto Julius Zobel was born on October 20, 1887 in Ripon, Wisconsin. He first studied at Ripon College, where he received his BA in 1909 with a thesis on Theoretical and experimental treatment of electrical condensers. He later received a Distinguished Alumnus Award from Ripon. He then went to the University of Wisconsin and graduated with an MA in physics in 1910. Zobel stayed at the University of Wisconsin as a physics instructor from 1910 to 1915, and graduated with his PhD in 1914; his dissertation concerned "Thermal Conduction and Radiation". This followed his 1913 co-authoring of a book on the subject of geophysical thermodynamics. From 1915 to 1916 he taught physics at the University of Minnesota. Having moved to Maplewood, New Jersey, he joined AT&T in 1916, where he worked on transmission techniques. In 1926, still with the company, he moved to New York and in 1934, he transferred to Bell Telephone Laboratories (Bell Labs), the research organisation created jointly by AT&T and Western Electric a few years earlier. He retired from Bell Telephone in 1952.