White Paper: Test & Measurement

dB or not dB? Everything you ever wanted to know about decibels but were afraid to ask...

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True or false: 30 dBm + 30 dBm = 60 dBm? Why does 1% work out to be -40 dB one time but then 0.1 dB or 0.05 dB the next time? These questions sometimes leave even experienced engineers scratching their heads. Decibels are found everywhere from power levels, voltages, and reflection coefficients to noise figures, field strengths, and more. What is a decibel and how should we use it in our calculations?

This Application Note is intended as a refresher on the subject of decibels. While this Application Note is not intended as a textbook, it will help to refresh your knowledge of this topic if you studied it before or provide a decent introduction if it is new to you.

Topics covered include why decibels are used in calculations, conversion from decibels to percentage and vice versa, using dB values in computations, and parameters that are measured in decibels. Tables are provided for quick reference when converting between decibels and linear values as well as when adding decibel values.

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