| 摘要 |
A digital sounder module (150) comprises: a sonar transducer (103) for transmitting an acoustic sonar wave at a selected frequency and pulse rate and for receiving echos of the transmitted acoustic sonar wave reflected from objects and for converting the received acoustic sonar wave into a first electrical signal; a band-pass filter (106) for providing a first wide bandpass filtration on the first signal to produce a second signal; an amplifier (110) for controlled amplification of the second signal to produce a third signal; the third signal being amplified carrier wave; an analog to digital converter (114) for receiving the amplified carrier wave , a rate at which the amplified carrier wave is converted to a digital signal by the analog to digital converter provides a harmonic sub-sampling , and the analog to digital converter transforms the amplified carrier wave into a digital intermediate frequency; a programmable logic device (118) for providing : (i) a variable gain control signal to the amplifier for normalization of the amplitude of reflected echos within the second signal by increasing gain in proportion to the distance of the echo reflection source from the sonar transducer; and (ii) the programmable logic device sets the harmonic sub-sampling rate cos Ô of the analog to digital converter such that the reflected transmitted acoustic sonar wave is above the Nyquist frequency; and a microprocessor (122) that provides an output for display (124) of the reflected echos.
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