| 摘要 |
PURPOSE:To detect a top signal pattern in a preamble from an input signal at high accuracy by providing a 1st band pass filter including a frequency component in its pass band and a 2nd band pass filter excluding a frequency component in its pass band. CONSTITUTION:The BPF 1 has a pass band characteristic with its nonmodulation carrier frequency as a center, and the BPF 2 has the characteristic of a pass band in the vicinity of the nonmodulation carrier frequency excluding said nonmodulation carrier band. When signals of a channel including the BPFs 1 and 2 arrive in a burstlike shape, the signal passing through the BPF 1 includes a preample signal at a nonmodualtion carrier frequency. Since the pass band of the BPF 2 excludes the nonmodulation carrier frequency, the signal passing through the BPF 2 is constant according as the preamble signal is received or not. Out of two powers inputted to a comparator circuit 7 through power calculation circuits 3 and 4 and LPFs 5 and 6, the power passing through the BPF l increases, and an output from the comparator circuit 7 exceeds a reference value. Finally a preamble detection signal is outputted from a detection circuit. |
