Digital sounder module and method for detecting

A method for detecting a sonar carrier wave comprising:

• receiving a sonar carrier wave;
• limiting the sonar carrier wave with an adjustable band-pass filter;
• amplifying the filtered sonar carrier wave with a two-stage differential variable gain amplifier wherein the gain of the amplifier is set by a gain curve received from a programmable logic device;
• inputting the amplified sonar carrier wave into an analog-to-digital converter, said analog-to-digital converter converts said amplified sonar carrier wave at a harmonic sub-sampling rate, cosφ, provided from said programable logic device to produce a digital intermediate frequency of the sonar carrier wave;
• controlling the amplifier and the analog-to-digital converter with said programmable logic device by digitally detecting and filtering the intermediate frequency sonar carrier wave by a noncoherent windowed in-phase/quadrature detector;
• compressing the digitized sonar carrier wave by a log2 function;
• and
• providing output from the programable logic device to a microprocessor and display.

A digital sounder module comprising:

• a sonar transducer for transmitting an acoustic sonar wave at a selected frequency and pulse rate and for receiving echos of said transmitted acoustic sonar wave reflected from objects and for converting said received acoustic sonar wave into a first electrical signal;
• a band-pass filter for providing a first wide bandpass filtration on said first signal to produce a second signal;
• an amplifier for controlled amplification of said second signal to produce a third signal, said third signal being an amplified carrier wave;
• an analog to digital converter for receiving said amplified carrier wave, a rate at which said amplified carrier wave is converted to a digital signal by said analog to digital converter provides a harmonic sub-sampling, and said analog to digital converter transforms said amplified carrier wave into a digital intermediate frequency;
• a programmable logic device, said programmable logic device implements a non-coherent windowed in-phase/quadrature (I/Q) detector and performs a Fourier transform of the intermediate frequency sonar return signal, said Fourier transform converts the intermediate frequency sonar return signal into a complex return signal which includes a real value that is an in-phase detected signal and an imaginary value that is a quadrature detected signal, said programmable logic device then multiplies the complex return signal by a window filter, said window filter sets said bandwidth and said frequency, said programmable logic device provides
• (i) a variable gain control signal to said amplifier for normalization of the amplitude of reflected echos within said second signal by increasing gain in proportion to the distance of said echo reflection source from said sonar transducer,
• (ii) a cosφ signal to said analog to digital converter, said programmable logic device sets said harmonic sub-sampling rate of said analog to digital converter such that said reflected transmitted acoustic sonar wave is above the Nyquist frequency, and
• (iii) a piecewise linear approximation of a log2 function, wherein the log value is linear approximated between all integer log2 values;
• a microprocessor, said microprocessor provides an output for a display of said reflected echos.