Underwater detection apparatus

An underwater detection apparatus comprising:

• a first transducer for transmitting and receiving ultrasonic signals on its operating frequency F1;
• a second transducer for transmitting and receiving ultrasonic signals on its operating frequency F2;
• a transmitter for generating a transmitting signal;
• a trap circuit for transferring the transmitting signal from the transmitter to the transducers and for passing an echo signal from the transducers;
• a preamplifier for amplifying the echo signal from the trap circuit;
• a mixer for converting the echo signal from the preamplifier into a signal of a specific frequency;
• a filter for selectively passing the signal of only the specific frequency-band output from the mixer;
• a main amplifier for amplifying the echo signal from the filter;
• an A/D converter for converting the echo signal from the main amplifier into a digital form;
• and
• a display circuit for displaying the digitized echo signal from the A/D converter on a monitor;
• wherein the trap circuit includes a coil and a diode, or a resistor and a diode, the first transducer and the second transducer are connected in parallel to the trap circuit via a low-pass filter and a high-pass filter, respectively, the transmitting signal of the transmitter is alternately switched between the operating frequency F1 of the first transducer and the operating frequency F2 of the second transducer, and wherein a locally generated signal fed into the mixer is alternately switched between two specific frequencies such that the mixer constantly outputs the signal of the fixed frequency regardless of whether the input echo signal has the operating frequency F1 or F2.

An underwater detection apparatus comprising:

• at least one transducer for transmitting and receiving ultrasonic signals;
• a transmitting signal generator for generating a transmitting signal of at least one frequency for driving the at least one transducer;
• a broadband trap circuit comprising a coil and a diode, or a resistor and a diode for transferring the transmitting signal fed from the transmitting signal generator to the at least one transducer selectively installed from multiple transducers and for passing an echo signal fed from the at least one transducer;
• a preamplifier for amplifying the echo signal fed from the trap circuit;
• a mixer for converting the echo signal of the at least one frequency fed from the preamplifier into a signal of a specific frequency;
• and
• a filter for selectively passing the signal of only the specific frequency-band output from the mixer.

An underwater detection apparatus comprising:

• an ultrasonic transducer for transmitting and receiving ultrasonic signals;
• a transmitting signal generator for generating a transmitting signal of a frequency for driving said ultrasonic transducer;
• a broadband trap circuit for transferring the transmitting signal from the transmitting signal generator to said transducer and for passing an echo signal fed from said ultrasonic transducer;
• a mixer for converting the echo signal of the frequency from said ultrasonic transducer into a signal of a specific frequency;
• a narrowband filter for selectively passing the signal of only the specific frequencies from said mixer;
• an amplifier for amplifying the echo signal from the filter;
• an A/D converter for converting the echo signal from the amplifier into a digital form;
• and
• an indicator for displaying the echo signal from the A/D converter.

An underwater detection apparatus comprising:

• an ultrasonic transducer for transmitting and receiving ultrasonic signals of a frequency;
• a transmitting signal generator capable of generating transmitting signals of a plurality of frequencies and outputting a signal of a frequency selected for driving said ultrasonic transducer;
• a broadband trap circuit for transferring the transmitting signal from the transmitting signal generator to said transducer and for passing an echo signal fed from said ultrasonic transducer;
• a local oscillator capable of generating local signals of a plurality of frequencies;
• a mixer for converting the echo signal of the frequency from said ultrasonic transducer into a signal of a specific frequency based on the echo signal and the local signal of a corresponding frequency selected;
• a narrowband filter for selectively passing the signal of only the specific frequencies from said mixer;
• an amplifier for amplifying the echo signal from the filter;
• an A/D converter for converting the echo signal from the amplifier into a digital form;
• and
• an indicator for displaying the echo signal from the A/D converter.

An underwater detection apparatus comprising:

• a first transducer for transmitting and receiving ultrasonic signals on its operating frequency F1;
• a second transducer for transmitting and receiving ultrasonic signals on its operating frequency F2;
• a transmitter for generating transmitting signals of the two frequencies at different times;
• a broadband trap circuit for transferring the transmitting signal from the transmitter to the transducers and for passing an echo signal from the transducers;
• a preamplifier for amplifying the echo signal from the trap circuit;
• a mixer for converting the echo signal from the preamplifier into a signal of a specific frequency;
• a filter for selectively passing the signal of only the specific frequency output from the mixer;
• a main amplifier for amplifying the echo signal from the filter;
• an A/D converter for converting the echo signal from the main amplifier into a digital form;
• and
• a display circuit for displaying the digitized echo signal from the A/D converter on a monitor.