Siemens CP 1515 Instructions d'exploitation télécharger pdf (Page 261)

Appendix

Operating Instructions SCALANCE W78x

C79000-G8976-C184-07

261

Designing and Calculating Wireless Systems Based on the

Example of RCoax

Calculating in Decibels

Decibels as a Logarithmic Unit of Measure

In wireless technology, most calculations are made in decibels (dB). Decibel

means the logarithm of a ratio. Formulated mathematically, this can be shown by

the following equation:

Decibel value = 10 * log (ratio)

Using sample calculations, the following decibel values are obtained:

Ratio Decibel Value

0.001 -30 dB

0.1 -10 dB

0.2 -7 dB

0.4 -4 dB

0.5 -3 dB

1 0 dB

2 3 dB

4 6 dB

As can be seen in the example, halving a value reduces the decibel value by 3 dB.

This remains true regardless of the selected reference variable because only the

ratio counts. Which reference variable is used can be recognized by the additional

letters or numbers following the dimension dB. In acoustics, for example, the

threshold of audibility is the reference variable for a value in dB(A).

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Siemens CP 1515 Instructions d'exploitation Page 261