CABLE BROADCAST SYSTEM, CABLE BROADCAST TRANSMITTER AND CABLE BROADCAST RECEIVER

摘要

PURPOSE:To send and receive contract information for each subscriber while multiplexing onto an audio signal. CONSTITUTION:A PWM modulation circuit 44 applies PWM modulation to a scramble key signal representing a synchronization suppression timing of a video signal according to contract information for each subscriber, an AM modulation circuit 12 AM-modulates an FM audio signal based on the PWM modulation output, a PWM demodulation circuit 46 of a receiver side demodulates the scramble key signal detected from the FM audio signal, and a CPU4 decoding the contract information enables synchronization regeneration of the video signal only when the subscriber receives a channel in compliance with the contract, then the system configuration is simplified by using the contract information multiplexed onto the audio signal together with the scramble key signal.