Abstract: A radar stability measurement system uses a microwave delay line that may be coupled between a standby transmitter and a standby receiver to test the stability of the standby channel in a radar system having at least two channels. A pulse output by the standby receiver is sampled in portions. Several samples of each portion are taken, samples are analyzed to produce a sum of residue power (P.sub.rm) and a sum of zero Doppler power (P.sub.om) for the m-th portion. After all samples of all portions have been taken, a single indicator of stability is calculated as ten times the log of the ratio ##EQU1## The measurement system can also be applied to single channel systems, although a short interruption of system operation may be necessary.