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.
Error Vector Magnitude (EVM) is a commonly used metric to measure the accuracy of a digital communication system. It quantifies the difference between the transmitted and received signal in terms of magnitude and phase.
EVM provides a comprehensive evaluation of the system’s performance by taking into account both amplitude and phase errors. The magnitude is calculated by determining the Euclidean distance between the ideal and actual received signal, while the phase is determined by calculating the angle difference between the two signals.
The EVM value is typically expressed as a percentage, with a lower value indicating a more accurate system. 1% EVM is more accurate than 2% EVM and therefore can support higher modulation complexity.
This metric is particularly useful in analyzing the performance of wireless communication systems, such as cellular or Wi-Fi networks. By measuring and monitoring the EVM, Radio systems engineers can assess the quality of the signal and make adjustments if necessary to optimize performance.
As we move toward higher wireless data rates with increasing complexity and higher order modulations, developing an understanding of EVM becomes more important.
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 – IQ mismatches are a result of receiver architectures. For example, while direct conversion radios require lower sampling rates and are more cost-effective, they suffer from IQ offsets.
- Frequency offsets and errors – Frequency shift and errors due to the reference oscillators result in higher EVM. Use the PPM to Hz calculator to find the frequency error.
- Phase noise
- AM-AM and AM-PM distortion
- Receiver noise figure – as the noise figure increases, the receiver sensitivity degrades and as a result the EVM increases
- Multipath fading
- RF Interference