Navigation and Seamanship

6.1.3.3. Receiver and Recorder

RECEIVER

The SONAR receiver is similar in operation to that of echosounder. The very weak signals that are returned from fish shoal or any target to the transducer are amplified to a sufficient magnitude and then sent to the display unit.

RECORDER

Since it is horizontal distance of an object from the vessel, the display of target on the sonargram( paper record of echos from sonar) may not give great details. A display which is better able to indicate distance and direction is the Plan Position Indication (PPI) on a CRT, which is similar to a radar display. The ship is the centre of the scope and the sonar beam can be seen travelling away from the ship on the bearing selected. If a target is detected the echo is shown on the screen, giving an indication of its range and bearing. The approximate depth of the target can be calculated from the distance and the angle of tilt. The audible indication of the echoes by loudspeaker is quite essential for the identification of various targets . An experienced operator can distinguish between different types of echoes better by the sound than from a paper record or CRT display .