This tool converts from dBm to dBu.
Formula
dBu = dBm – 27.78 + 10*Log10(Z)
where Z is the impedance
If the power is specified in Watt, convert the number to dBm first.
Example Calculations
A value of 30 dBm (1 Watt) is equivalent to 19.2 dBu when the impedance is 50 ohm.
Background
What is dBu?
dBu is the RMS voltage relative to 0.7746 Volt.
1 VRMS is therefore equivalent to 20*Log10(1/0.7746) = 2.218 dBu.
The inverse relationship or conversion from dBu to VRMS is defined by the formula VRMS = 10(dBu / 20) x 0.7746.
Notes:
- dBu is different from dBV which is the RMS voltage relative to 1 Volt. dBV to dBm Calculator.
- dBu is also not the same as dBuV or dBµV which is the RMS voltage relative to 1 microvolt. dBµV to dBm Calculator.
Where does the number 0.7746 come from?
It is the value of voltage that dissipates 1 milliwatt (mW) into a 600 ohm load. Reference: Wikipedia article on dB Voltage
V = √(600Ω * 0.001W) Volt = 0.7746 V
dBu was originally dBv, however it was changed to what it is today to avoid confusion with dBV. Wikipedia Reference.
What is dBm?
dBm stands for deciBel referenced to 1 milliwatt. It is an absolute unit of power. The following formula is used to convert Watt to dBm:
PdBm = 10*log10(1000*PW)
where
- PW is the power expressed in watt.
- PdBm is the power expressed in dBm