This tool converts from dBm (dB-milliwatt) to dBuV (dB-microvolt).
- The default impedance is 50 Ω although it can be changed to any value.
- Microvolt is a Root-mean-square (RMS) quantity
dBμV = dBm + 10*Log10(Z) + 90
-90 dBm into 25 ohm gives a value of 14 dBμV.
What is dBm?
dBm is a unit of power and there is a direct relationship to Watt. It is used by RF engineers in the characterization of radio components and modules. For example, amplifier output saturation level might be +10 dBm, mixer LO drive level might be +17 dBm.
dBm can be used in conjunction with RF gains and losses to calculate what the maximum input to and expected output from a section of a circuit is expected to be.
What is dBμV?
dBμV (often written as dBuV) or deciBel referenced to 1 microvolt. The formula to convert from µV to dBµV is given by
dBµV = 20*Log10(µV)
In the area of Electromagnetic Compatibility – in particular the measurement of conducted emissions, the units dBμV are used. dBμV is written as dBuV for simplicity. A larger range of values can be expressed on the dB scale.
The plot below shows the screen of a Siglent Spectrum Analyzer that’s used to make a conducted emission test.
The vertical axis shows the level in dBuV. Using the dB scale instead of linear (uV) allows for a larger range of values to be shown.
The blue line shows the conducted emissions limits while the yellow lines show the actual measurement data. If at any point, the yellow were to exceed the blue, the device under test would be considered as failed to meet specification.
 Conducted emissions uses dBuV while radiated emissions uses dBuV/m. The FCC stipulates limits for each. The picture below shows a table for FCC Part 15 conducted emission limits as a function of frequency up to 30 MHz.
The calculator on this page provides conversion between dBm to dBuV while this calculator allows conversion from dBm at the output of an emitter to dBuV/m at a distance of 3 meters.
 dBuV is not the same as dBu. dBuV is referenced to 1 microvolt, while dBu is referenced to 0.7746 V. Use this tool to convert dBu to dBV.
 Electromagnetic Compatibility on Wikipedia