| 摘要 |
<p>Radio waves used in broadcasting and communications making use of broadcasting satellite and communication satellite are FM signals, and the frequency shift and exclusive bandwidth vary depending on the modulation signal. The satellite broadcasting receiver is designed to control the frequency shift so that the amplitude of the demodulation signal be constant, thereby making uniform the bandwidth of the intermediate frequency filter, so as to be capable of receiving by one filter. At this time, the frequency shift can be controlled continuously, from large to small one, in a predetermined exclusive bandwidth. When further expandlng the frequency shift, since the exclusive bandwidth is extended, and the noise electric power is increased and the receiving sensitivity is lowered as compared with the exclusive machine. Accordingly, when expanding the frequency shift, the noise bandwidth is narrowed in the PLL demodulator, thereby enhancing the receiving sensitivity.</p> |
