ABSTRAT Digital radio-relay systems are particularly affected by the frequency selective nature of multipath fading. To know the effects of propagation on radio-relay systems, an experimental measurement setup was realized to characterize their susceptibility to multipath distortion.The setup is basically a recorder of the frequency-selective amplitude and group delay variations. Associated to these informations, data of error presence (single error, error burst, BER, etc.) are collected to determine, by successive elaborations, relationships between error occurrence and critical values of amplitude and group delay distortions. The measured data are stored only when they exceed the prefixed reference masks. Preliminary results are reported.