| 摘要 |
PROBLEM TO BE SOLVED: To readily perform a carrier search, on a direct-conversion method receiver for digital satellite broadcasting which mixes a received RF signal and a locally oscillated signal, having nearly same frequency of RF signal that should be received and being different by 90 degrees in phase from the RF signal by a local oscillator at a mixer, gives I/Q signals of the obtained base-band components to a digital decoding means realized by LINK IC, etc., via each of variable low-pass filters, and performs digital decoding to the base- band signal. SOLUTION: This receiver widely sets up the pass-band of the above filters by S14, after selecting a broadcasting station by S13. With this means, the I/Q signals enter the pass-band, even if the RF signal is offset by a LNB, etc., and optimizes the essential pass-band matched to the transmitting rate by S18, if the locking of the LINK IC is confirmed by S17. As a result, the receiver can readily perform carrier search and can be select the desired channel, in a short time and with certainly. |
