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).
