Surface wave delay line for TV signal de-scrambler - has transducer transmitter radiating wave signals from centre track through couplers to transducer receivers

摘要

A surface wave delay line device for use in descrambling television transmission signals according to a given key comprises three adjacent tracks (A,B,C) on a piezoelectric support such as a lithium niobate crystal. The centre track (B) has an input transducer which receives the intermediate frequency t.v. signal and transmits surface waves symmetrically in both directions on the track. A respective coupler (R1,R2) on each side of the transducer transfers the wave energy to both outer tracks (A,C) where the energy is received by four transducer receivers (TS1-4), two per track, at selected distances from the input transducer axis. The receivers are selectively connected to a common output in accordance with the key so that the delays in the component transmitted signals are equalised to reconstitute the required video signal.