This calculator finds the difference between two deciBel (dB) values.
Let’s say you have an RF attenuator with a value 30 dB followed by an amplifier with gain 20 dB.
- The total attenuation is 30 dB – 20 dB = 10 dB
- The total amplification is 20 dB – 30 dB = -10 dB
What does dB difference mean?
The deciBel equivalent of a number X is given by XdB = 10*Log10(X)
Similarly the dB equivalent of a number Y is YdB = 10*Log10(Y)
The dB equivalent of X/Y is 10*Log10(X/Y) = 10*Log10(X) – 10*Log10(Y)
The difference between two dB numbers is equivalent to the Log of the ratio of the linear equivalent of the two.
In the above example, the RF attenuator has a value of 30 dB which means it attenuates the signal by a factor of 1000. Alternatively, it amplifies the signal by -30 dB = (1/1000).
The RF amplifier has a value of 20 dB which means that it amplifies the signal 100 times.
To calculate the effective gain we calculate the product of the two numbers: (1/1000)*100 = 1/10.
The Logarithm of 1/10 is 10*Log10(1/10) = -10 dB which represents the total or cascaded gain.
The same number was found by adding the gain numbers in dB: 20 dB – 30 dB = -10 dB
Table of dB Difference vs Linear
This table provides the dB difference between two numbers and the ratio of the linear equivalent
|dB Difference||Linear Ratio|
- dBm Addition – Add two power values in dBm doesn’t follow the same rules as adding two dB values
- dB Addition – follows the same rules as subtraction