Decibel--The Name for the Transmission Unit

Decibel--The Name for the Transmission Unit By W. H. MARTIN N 1923 the "mile of standard cable" was replaced in the Bell System by a new unit for expressing telephone transmission efficiencies and levels. At that time the generic term "transmission unit" was taken to designate this new unit, since it was considered desirable to defer the adoption of a more distinctive name until this unit had been given further consideration by others who would have use for a unit of this type. This new unit is defined by the statement that two amounts of power differ by one transmission unit when they are in the ratio of 10·1, and any two amounts of power differ by N transmission units when they are in the ratio of l(F ( -°. In accordance with this, the number of transmission units corresponding to the ratio of any two powers is ten times the common logarithm of that ratio. For a unit of this kind, it is evidently desirable to have universal use. Accordingly, the Bell System, prior to its adoption of the transmission unit, discussed this matter with various foreign telephone administrations, and suggested their consideration of the use of the proposed "transmission unit." A number of these administrations expressed a favorable attitude towards this unit. In 1924 there was organized the International Advisory Committee on Long Distance Telephony in Europe. The purpose of this committee, which is composed of representatives of the various telephone administrations of Europe, is to recommend standards and practices for the development of telephone sen-ice between the European countries.