The residual BER - error floor, though useful and widely used metrics for the end-to-end digital radio transmission performance, provides no insight into the error-generating analog impairments (e.g. modulation signal inaccuracy, power amplifier compression, carrier recovery phase error, or I-Q cross- talk), which, however, are easy to identify (so can be dealt with) by the VSA tools such as constellation analysis. Moreever, even this cannot help notice minor distortions that can still seriously degrade the performance, so the only option is the EVM analysis, which has become very popular figure of merit in this regard. So in this paper, after reviewing crucial advantages of EVM analysis with respect to what we get from BER, we consider estimating EVM from the residual BER assuming that the latter's generally non-linear and non-additive "constituents" are substituted by the equivalent additive Gaussian noise source producing the same BER (and EVM) degradation.