This calculator allows you to convert between dB and percent (%) values of Error Vector Magnitude.
How to use the Calculator
Enter either quantity and the other will be calculated. Note:
- EVM (dB) is a negative value
- EVM (%) is a positive value
Example EVM Calculation
An EVM value of 1% translates to -40 dB. As the percent value increases so does the dB value. The maximum is 100% which translates to an EVM of 0 dB.
What is EVM?
Error Vector Magnitude is a measure of modulation quality in a communication system. It is the ratio of the average of the error vector power (Perror) to the average ideal reference vector power (Pref). Since it is a ratio, it has no units.
EVM = Perror/Pref
EVM (dB) = 10*LOG10(Perror/Pref)
EVM (%) = SQRT(Perror/Pref) * 100
EVM dB vs percentage
It’s a matter of preference. Some engineers and technologists are used to a logarithmic scale, i.e. dB while others like to see it as a percent value.
Major Factors that Influence EVM
Here is a list of impairments that have an influence on EVM:
- IQ mismatch in transmitter and/or receiver
- Frequency offsets
- Phase noise
- AM-AM and AM-PM distortion
- Receiver noise figure
- Multipath fading
- RF interference