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Figure 46-Doppler effect. A. One-second audio signal. B. One sine wave of the audio signal.
AIRBORNE SONAR SYSTEM

Aviation Electronics Technician 1 (Organizational)
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Figure 4-7.-Transducer installed on a moving ship. If the transducer is aimed perpendicular to the direction of motion, the particles in the water will echo the same note sent out because the transducer is neither going toward the particles nor away from them. (See figure 4-7.) Now consider the echo from the submarine, shown in figure 4-8. Again, the transducer is shown stationary. When the submarine is neither going toward nor away from the transducer, it must be either stopped or crossing the sound beam at a right angle. If it is in either condition, it reflects the same sound as the particles in the water. Consequently, the submarine echo has exactly the same pitch as the reverberations from the particles. Figure 4-9.-Comparison of echo frequency and reverberation frequency when submarine moves toward transducer. Suppose that the submarine is going toward the transducer, as shown in figure 4-9. It is as though the submarine is the train heading toward the car that is blowing its horn at the crossing. The horn sounds higher as the train approaches the car. In the same manner, the sound beam sounds higher to the submarine as it approaches the transducer. Figure 4-8.-Transducer supported by helicopter. Doppler effect is absent when submarine is stationary or moves at right angles to sound beam. Figure 4-10.-Comparison of echo frequency and reverberation frequency when submarine moves away from transducer. 4-8







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