Radio duplexing system for interactive DVB-T has bandstop filters fed from hybrid couplers with residual unlink leakage cancellation

摘要

A radio duplexing system has a 3 dB hybrid coupler (2) combining the downlink (d) and unlink (m) signals into in phase and orthogonal outputs fed to tunable (cf) bandstop filters (31-1, 2) in a downlink extraction unit (3) that reflect the unlink signal (me) to the antenna (1) and pass the downlink to a residual filter (4) . Includes an Independent claim for construction of the residual filter by gain (cg) and frequency (cf) controlled subtraction (42) of a sample of the unlink signal.