SOUND SENSING UNIT IN UNDER WATER SOUND DETECTOR

摘要

PURPOSE:To suppress the doppler shift, by mixing the signal frequency-dividing the reflected frequency signal from the object under water with the local oscillation frequency signal at the 1st mixer, mixing the signal through the 1st filter with the reflected frequency signal at the 2nd mixer, and picking up the audible frequency signal at the 2nd filter. CONSTITUTION:The reflected frequency signal reflected from the object in water enters from the input terminal Pi and shaped at the shape circuit into a rectangular wave and frequency-divided at the frequency divider 2 into 1/n. This frequency signal fi/n and the oscillation frequency signal fo of the local oscillator 4 are mixed at the mixer 3, to deliver the frequency signal of (fi/n+ or -fo) from the filter circuit 5. This frequency signal and the input frequency signal fi are mixed at the mixer 6, and the audible frequency signal of (fi/n+fo)-fi is picked up via the filter circuit and audible tone is delivered from the speaker 9 via the amplifier 8. By setting the center value fbo of the audible frequency fo as fbo=fo-fio(n-1)/n, where; fio is the center frequency of fi, the amount of doppler shift can be suppressed to (n-1)/n.