An experimental method for the study and trial ofN-hop digital microwave radio systems is described. The method is particularly useful for those systems where the different disturbances accumulate and do not occur on each hop on an independent basis. The method simulates a digital transmission system by generating an information sequence ofmbits at a rate of fbbits/s and circulating the sequenceNtimes through one regenerator and a coaxial cable loop having a time delay\tau > m/f_{b}. The circulating loop can be employed to investigate the influence on noise and error rate in digital radio systems of factors such as: cochannel and intersymbol interference; heavy rain attenuation on one or two repeater sections; additive noise; gain and phase nonlinearities; fading; changes in components and operating conditions within the regenerator; and combinations of these disturbances occurring simultaneously.