Unit of transmission and the transmission reference system

Very early in the life of the telephone industry it became evident that the handling of transmission problems required the establishment of a unit of transmission in terms of which different circuits could be compared, the effect of changes in the telephone plant could be stated, and the usefulness of a given circuit for transmitting conversations could be expressed. The author discusses the various units of transmission and outlines the reasons for adopting the T.U. or db (decibel) in America and England, and the Neper on the Continent, as units for measurements in telephone systems. The Transmission Reference System is designed to function as a standard telephone circuit, and all corresponding apparatus will be referred to its counterpart in it. The reference transmitter is a condenser transmitter calibrated by the thermophone; the reference line is a distortionless resistance line; and the reference receiver is a moving-coil receiver, miniature to that described by Wente and Thuras [see Abstract 1928B00879]. The reference system as a whole is practically distortionless over the voice-frequency range.