| 摘要 |
<p>A frequency agile modulator which modulates input baseband video and audio signals to a selected NTSC channel. The modulator includes a microprocessor which has as inputs a channel up push-button switch and a channel down push-button switch. An amplifier stage of the modulator is turned off by the microprocessor when the channel is being changed. A low pass noise limiting filter and a high pass noise limiting filter are connected in parallel between the amplifier stage output and the output of the modulator and, depending upon the selected channel, either one or the other of the filters is inserted in the signal path by the microprocessor. Equalizer circuitry is provided at the output of the modulator so that lower frequency signals are transmitted at a lower level than higher frequency signals.</p> |
