Acoustic Doppler Detector.
DEPARTMENT OF THE NAVY WASHINGTON DC
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An oscillator generates a fixed frequency ultrasonic output signal. After power amplification this signal drives a transmitting transducer which projects an ultrasonic beam into water. Reflected signals are received by a receiving transducer and AGC preamplified. A chopper multiplies the received signal with the transmitted signal and generates an output signal if a target exists. To determine whether the target is a swimmer, this output signal is band pass filtered and amplified and then fed both to an automatic alarm and to a set of headphones. A human operator listening to the headphone output classifies the target and determines exact bearing. Author
- Acoustic Detection and Detectors