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An empirical relationship relating the mean quasi-instantaneous rainfall rate along a microwave path and the signal attenuation over the path at 11 GHz has been obtained and is compared with a theoretical formula derived by Ryde. A relationship between the annual distributions of several measured point rainfall rates for periods of 2, 10, 20 and 60min has also been obtained. This has been used, in conjunction with the empirical rainfall-rate/attenuation relationship and hourly point rainfall-rate distributions measured at points on several experimental 11 GHz microwave paths, to synthetise annual distribution curves of quasi-instantaneous attenuation due to rainfall according to a method proposed by Bussey. These curves are compared with characteristics measured on the paths. A method developed by the UK Post Office for predicting attenuation by rainfall at microwave frequencies is also described. Distributions of attenuation determined by this method for the experimental paths are also compared with the measured distributions. Several published methods of predicting hourly point-rate distributions from generally available coarse rainfall statistics have been examined which, if satisfactory, would have provided a powerful means in conjunction with the Bussey method for predicting the effect of rainfall on a microwave path. It is shown, however, that these methods give results which, when compared with measured performance, are far from satisfactory. Of the methods for predicting attenuation by rainfall studied, the Post Office method appears to justify most confidence and to be the easiest to use.