| 摘要 |
A radio frequency signal modulator automatically controls the input audio signal level. The radio frequency signal modulator includes: a pre-emphasis part for previously emphasizing a specific frequency band; a FM modulator for modulating a frequency of an audio signal; a middle carrier frequency generator for generating an audio middle broadcasting frequency; AM modulator for modulating an amplitude of an image signal; a carrier frequency generator for generating the image and audio channel frequency; a RF signal mixer for mixing the audio RF signal and an image carrier wave; and au automatic level controller(70) which is connected to a front end of the pre-amphasis part, and automatically controls the audio signal with a predetermined level. Accordingly, the radio frequency signal modulator automatically adjusts the input audio signal to a level being previously allowed before a frequency modulation, thereby preventing the audio signal's interference influenced on the image.
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