SCRAMBLER, ENCODER AND DECODER FOR THE SAME SCRAMBLER

摘要

PURPOSE:To attain a scramble processing for a TV broadcasting signal by mixing a modulation signal modulating a carrier with a video base band signal and an audio base band signal with a local oscillation signal generated by specifying the modulation signal. CONSTITUTION:An intermediate frequency modulation section 2 uses a base band video signal inputted from a video signal input terminal 2a to apply AM modulation to a video carrier in a prescribed frequency and uses an audio signal inputted from a base band audio input terminal 2b to apply FM modulation to an audio carrier. The generated intermediate frequency modulation signal fIPM is added and mixed with a local oscillation signal supplied from a local oscillation section 6 at a mixer section 4. The local oscillation section 6 uses an FM modulation section 8 to apply FM modulation with a signal from a signal source 10, thereby generating a local oscillation signal frequency- shifted from a reference frequency over a wider range than a pull-in enable frequency range of a conventional automatic frequency control circuit. Thus, a TV broadcast signal is scrambled.