The blind separation problem of analog modulated radio signals and their DOA (Direction Of Arrival) estimation problem are considered. These problems are very important in radio surveillance. Based on the idea of Carlos and Takada [1], the following two methods are proposed for an Independent Component Analysis (ICA) based radio surveillance system. The first method is concerned with the improvement of DOA estimation accuracy after signal separation by ICA. Another method treats separation and DOA estimation in multipath environment. The effectiveness of the proposed methods is proved by computer simulation.