| 摘要 |
<p>RCA 79,040 CANADA A televison transmitter uses a diplexer to combine the signals from a visual power amplifier and an aural power amplifier. The diplexer uses hybrids coupled together by transmission lines, and the transmission-lines have aural frequency cavities which reflect the aural energy from the aural input to the output port for application to an antenna or other utilization device. In the event that the aural power amplifier fails, it is desirable to revert to multiplexed operation, in which the visual amplifier amplifies combined visual and aural signals. This mode of operation is accomplished by switching the low-level aural signal for combining with the low-level visual signal and by simultaneously switching the tuning of the aural cavaties, so that they do not undesirably reflect the aural energy back to the visual input port.</p> |
