Automatic shutdown arrangement for stand-alone television modulator

A stand-alone modulator for modulating a signal carrier with a video information modulating signal obtained from a selected video signal source and applied to a modulating signal input terminal capable of being connected to any one of a plurality of video signal sources, including overmodulation protection circuitry, comprising:

• a source of energizing potential;
• carrier generating and modulating means coupled to said modulating signal input terminal for generating said signal carrier and modulating said signal carrier in response to variations in the amplitude of said video information modulating signal obtained from said selected one signal source, said carrier generating and modulating means when energized by said energizing potential capable of being operated in an overmodulated condition to overmodulate said signal carrier when the amplitude of said video information modulating signal exceeds a predetermined overmodulation level;
• comparator means having first and second switching states, said comparator means being coupled to said source of energizing potential and having an output terminal coupled to said carrier generating and modulating means for applying said energizing potential to at least a portion of said carrier generating and modulating means when said comparator means is in said first switching state when said amplitude of said video information modulating signal is below said predetermined overmodulation level;
• means for developing a voltage representative of the amplitude of said video information modulating signal;
• means for developing a reference voltage representative of an amplitude of said video information modulating signal that is capable of producing said overmodulated condition;
• and
• means for applying the above two recited representative voltages to said comparator means to switch said comparator means into said second switching state upon the occurrence of said overmodulated condition, said comparator means removing energizing potential from said carrier generating and modulating means when in said second switching state, thereby providing overmodulation protection.