![]() This unit was employed up to 1923 when a new unit was adopted as being more suitable for modern telephone work. The introduction of cable in 1896 afforded a stable basis for a convenient unit and the "mile of standard" cable came into general use shortly thereafter. Since the earliest days of the telephone, the need for a unit in which to measure the transmission efficiency of telephone facilities has been recognized. The naming and early definition of the decibel is described in the NBS Standard's Yearbook of 1931: The bel is seldom used, as the decibel was the proposed working unit. It was named the bel, in honor of the telecommunications pioneer Alexander Graham Bell. In 1928, the Bell system renamed the TU into the decibel, being one tenth of a newly defined unit for the base-10 logarithm of the power ratio. The definition was conveniently chosen such that 1 TU approximated 1 MSC specifically, 1 MSC was 1.056 TU. 1 TU was defined such that the number of TUs was ten times the base-10 logarithm of the ratio of measured power to a reference power. In 1924, Bell Telephone Laboratories received favorable response to a new unit definition among members of the International Advisory Committee on Long Distance Telephony in Europe and replaced the MSC with the Transmission Unit (TU). A standard telephone cable was "a cable having uniformly distributed resistance of 88 ohms per loop-mile and uniformly distributed shunt capacitance of 0.054 microfarads per mile" (approximately corresponding to 19 gauge wire). 1 MSC corresponded to the loss of power over one mile (approximately 1.6 km) of standard telephone cable at a frequency of 5000 radians per second (795.8 Hz), and matched closely the smallest attenuation detectable to a listener. Until the mid-1920s, the unit for loss was Miles of Standard Cable (MSC). The decibel originates from methods used to quantify signal loss in telegraph and telephone circuits.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |