Industry White Paper

# dB or not dB? Everything You Ever Wanted to Know About Decibels But Were Afraid to Ask…

January 01, 2023 by Rohde & Schwarz
Topics Covered
• Why Use Decibels in Our Calculations?
• Conversion from Decibels to Percentage and Vice Versa
• Using dB Values in Computations
• What Do We Measure in Decibels?

### Application Note Overview

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, including power levels, voltages, reflection coefficients, 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.

• M
mstoynov September 05, 2021

Can decibels be a decimal fraction, for example 6.25 dB?  Or in that case to choose the closest value like 6dB?
I am trying to calculate the CMRR of the second stage of the instrumental amplifier and the value obtained is 6.25dB.

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• A
absintheaudio January 05, 2023
dB is merely a ratio, so yes, it can have decimals
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• D
dalewilson January 05, 2023
This textbook page provides some more insights into decibels that might be helpful to you. https://www.allaboutcircuits.com/textbook/semiconductors/chpt-1/decibels/
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