| 摘要 |
<p>A hierarchical transmission digital demodulator which can perform stable synchronism establishment and stable demodulation by setting its demodulating operations based on a reception C/N value. The reception C/N value is measured by a CNR measuring circuit (10) upon receiving the demodulated output of an arithmetic circuit (1). Carrier reproduction is performed based on a demodulated output obtained by demodulating the modulated wave in a header section and the modulated wave of a burst symbol signal during the period until synchronism establishment, and, after synchronous acquisition, performs the demodulation output in the header section based on the output of a logical gate circuit (11) and carrier reproduction based on the burst symbol signal and a QPSK signal when the C/N value is intermediate. When the C/N value is high or low, the demodulator switches a carrier reproducing loop to a higher gain by means of a gain control circuit (8) based on a signal from the logical gate circuit (11).</p> |
