| 摘要 |
PROBLEM TO BE SOLVED: To receive signals in a satisfactory CN ratio regardless of the transmission mode by discriminating the transmission mode of the received signal which is obtained by a tuning means and changing the loop characteristic of a PLL based on the discriminated transmission mode. SOLUTION: A controller 18 decides a received band and then estimates and measuring the initial characteristic of a proper PLL loop. Then the controller 18 sets the initial characteristic and decides whether a null part (non-signal part) is included in a received signal based on the detection result of a null detector 20. If the null part is detected, a received mode is decided by deciding the frequency where a null part occurs and then deciding the length of the null part, for example. When the transmission mode of the received signal is decided, the controller 18 properly updates the setting of an LPF 23 to secure the PLL loop characteristic that is suitable to the transmission mode of the received signal. Thus, the signals can be received with a satisfactory CN ratio regardless of the transmission mode. |
