A PC-based coherent sonar for experimental underwater acoustics

An important tool for experimental underwater acoustics research is a versatile sonar system for transmitting, receiving, anti recording acoustic waveforms. In this paper the design, implementation and performance of a variable-frequency (25 kHz to 500 kHz) coherent sonar are presented. The significance of the design lies in its simplicity and versatility. These attributes are a result of a sampling technique that provides quadrature samples of the complex envelope of a bandpass signal without analog demodulation using a single A/D converter. Implementation of the design is accomplished using an ISA bus personal computer (PC), a commercially available digital signal processing (DSP) board, and a small amount of custom electronics. Performance of the sonar, in terms of magnitude and phase errors, is determined from wideband noise characterization, a linear-system model, and transmit/receive measurements.