. The Bell System technical journal . nding index forthe power ratio giving the effect of the combination of these parts. The mile of standard cable is such a logarithmic function of a[xiwer ratio. The new unit also meets this important recjuirement. OF THK IMt The transmission unit (abbreviated TV) has been chosen sothat two amounts of power differ by one transmission unit when theyare in the ratio of 10° and any two amounts of power differ by Aunits when they are in the ratio of lO-^. The number of trans- 402 BELL SYSTEM TECHNICAL JOURNAL mission units corresponding
. The Bell System technical journal . nding index forthe power ratio giving the effect of the combination of these parts. The mile of standard cable is such a logarithmic function of a[xiwer ratio. The new unit also meets this important recjuirement. OF THK IMt The transmission unit (abbreviated TV) has been chosen sothat two amounts of power differ by one transmission unit when theyare in the ratio of 10° and any two amounts of power differ by Aunits when they are in the ratio of lO-^. The number of trans- 402 BELL SYSTEM TECHNICAL JOURNAL mission units corresponding to the ratio of any two powers Pi andPo, is then the common logarithm (logarithm to the base 10) of theratio P] Po, divided by This may be written N= 10 logio P\ .V is a logarithmic function of the power ratio, any two numbersof units, jVi and A^2. corresponding respectively to two ratios, Pa/Pb 5L3ni3rd Corrnlon Standard Cwr>mon Batitcry Sub-station Adjustable length of Standard Cable SattcrySjb-staton Set -^ Set. Fig. 1 and Pc/Pd, may be added and the result A^ + As, will correspondto the product of the ratios, From the above it is seen that the measure in transmission unitsof the ratio of two amounts of power P\ and P-i is .V, where log Pi iV = log 10« In other words, the transmission unit is a logarithmic measure of powerratio and is numerically equal to log lO^. The reasons for the selection of this unit and the method of ap-plying it, can probably be best brought out by a consideration of thepractise which has been followed in determining and oxprassing theefficiencies of telephone circuits and apparatus in tirnis ot Tuilesof standard cable. Standard Referenck (ik( i it Fig. 1 sliiiws what lias been designated the stamhud referencecircuit. It ((insists of two common liattery telephone sets of thetype standard in the Bell System at the time this circuit was adopted,connected through repeating coils or transformers to a \ariable lengthof st
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
