DESCRAMBLING SYSTEM CATV TERMINAL

PURPOSE:To perform voice control freely and descramble a signal with a base band signal by detecting a TV-RF signal which is so scrambled and modulated as to perform volume control, and converting the base band signal. CONSTITUTION:The scrambled and modulated TV signal is applied from a CATV signal input terminal 1 to a tuner 15 to perform frequency conversion, and a video carrier IF signal is extracted through a filter 16 for video carrier IF signal extraction. This signal is detected by a detector 18 and applied to a multiplier 21. An audio carrier IF signal is extracted from the output of the tuner 15 through a filter 23 for audio carrier IF signal extraction, and an envelope detector 25 detects a scrambled sine-wave signal in the carrier signal. This signal is applied to a filter 26 for scrambled sine wave signal extraction to remove its noise component, and the output of the filter is applied to the multiplier 21 through a phase adjusting device 27 and a pre-distortion circuit 36. The multiplication between the scrambled sine wave and video signal is controlled with the control signal from a control terminal 31 to perform descrambling.