A correlation function measuring method and apparatus can correct a correlation vector with high accuracy. It relates to an active duplexer with full-duplex operation, permitting simultaneous transmission and reception of signals at same or different frequencies. The pair of source-follower transistors are respectively coupled between the pair of input terminals and a bulk terminal of the pair of bulk-driven input transistors. The terrestrial segment manages the communications link between one or more cellular service providers who are accessing the terrestrial segment and the mobile platform.