This calculator converts from dBuV (dB microvolt) to dBm (dB milliwatt). The default impedance is 50 ohm although you can change it to any value.
Formula
dBm = dBμV − 10*Log10(Z) − 90
Example Calculation
A value of 1 dBuV into 50 ohm gives -106 dBm.
Background
dBm stands for deciBel relative to 1 milliwatt. It is used by RF engineers to specify absolute power levels in an RF circuit. dBm can be converted to Watt when required.
dBuV stands for deciBel relative to 1 micro-volt. The symbol for micro is µ. However for ease, it’s often written as u instead. dBuV is often used to specify receiver sensitivity as a voltage.
Example Applications
Two way radio sensitivity
For instance, the sensitivity of a Baofeng UV-5R is 0.2 uV with 12 dB SINAD [1]. This is equivalent to -14 dBuV (using the uV to dBuV converter). The dB scale makes it easier to represent large and small numbers.
The calculator on this page can be used to convert -14 dBuV to -121 dBm.
The sensitivity of the RT-85 which is a comparable product from Retevis has a sensitivity of less than or equal to 0.2 uV.
A smaller number implies the radio receiver inside is more sensitive. However, in the case of Retevis, they don’t really tell you how much better it is than the UV-5R. Nor does Retevis tell you what the SINAD is. It can get a little tricky sometimes to compare radio product specifications!
Radio Emissions
Radio system designers have to ensure that the final product meets FCC limits on both conducted and radiated emissions.
Conducted emissions must be kept low or they can propagate through cables and interface connectors causing Electromagnetic Interference (EMI) to other electronic devices. EMI can flow through a common power supply or connected cables and can cause devices to malfunction.
FCC specifies limits on these emissions as shown in the table below. The frequency range varies from 0.15 MHz to 30 MHz.
The picture below shows a plot of emissions from a power amplifier module. The red line indicates the limits while the black plot represents the actual measurement.
The y-axis of the plot shows dBuV values ranging from 20 dBμV to 80 dBμV.
An RF designer can convert this range of values to their dBm equivalent shown in the table below.
| dBuV | dBm |
|---|---|
| 20 | -87 |
| 80 | -27 |
RF system budget calculations are performed using dBm and dB values. For instance, a receiver is designed to accept a range of input level values in dBm. End-to-end gain or gain at various stages in the circuit are specified in dB.
RF designers use component specifications for reverse isolation S12 for example, to determine dBm levels at the RF input. The dBuV specifications as shown above are converted to dBm using the calculator. They then guide the max dBm power levels as a result of various factors in the RF design.
Related Calculators
Notes
[1] SINAD stands for Signal-to-Noise and Distortion Ratio. It is a measure of signal quality.