| 摘要 |
PURPOSE:To detect an echo in a received signal securely even in case of variation in speed and variation in echo frequency and to simplify circuit constitution by providing an NB.BPF which attenuates only the echo. CONSTITUTION:The circuit 20 consisting of the NB.BPF21, a phase inverter 22, and an adder 23 functions to reduce only an echo. If an underwater sailing body varies in speed and the frequency of the echo varies, an input and an output signal to and from the NB.BPF21 has a phase difference and a detection signal (d) is outputted from a phase detector 17 and supplied through a switch circuit 25 to an integrator 18, whose integral output is supplied to an adder 26. Then, a signal (f) of frequency corresponding to its addition output signal is outputted from a VCO19 to a multiplier 12. Consequently, the frequency of the output signal (m) of the multiplier 12 is controlled to ZHz to reduce the phase difference between the input and output signals to and from the NB.BPF21. |
