The invention relates to a method for measuring the fade margin in a radio
system. The system comprises at least one transmitter (11a; 11b) and at
least one receiver (12b; 12a) which in an operational situation establish
a fixed radio connection. In the method, the receiver is calibrated by
supplying the receiver with an input signal at several different power
levels and determining the correspondence between the supplied signal
level and a quantity detected by the receiver. To enable the fade margin
to be determined as simply as possible, (a) the calibration is carried out
in such a way that at least one supplied power level is close to the noise
level of the receiver, (b) in a situation where substantially mere noise
is suued into the payload signal, a threshold value (PTH1) for the
received signal level, corresponding to a predetermined bit error ratio,
is determined for the receiver (c), in an operational situation of the
radio system, the signal level arriving at the receiver is determined
without payload signal, (d) on the basis of the calibration data and the
level determined in step (c), that threshold value for the received signal
level which corresponds to said predetermined bit error ratio in the
operational situation of the radio system is determined, and (e) the fade
margin is determined on the basis of the threshold value for the
operational situation and the signal level measured in the operational
situation of the system.