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2-1
2. FINE TUNING THE SONAR PICTURE
2.1 Eliminating Unwanted Echoes
Echoes from targets such as bottom and fish return to the transducer in order of
distance to them, and when we compare their intensities at the transducer face,
those from nearer targets are generally stronger when their reflecting properties
are nearly equal. The sonar operator will be quite inconvenienced if these
echoes are directly displayed on the screen, since the actual size of the target
cannot be judged from the size of echoes displayed on the screen. To overcome
this inconvenience, the TVG function is incorporated. It compensates for
propagation loss of sound in water; amplification of echoes on short rang is
suppressed and gradually increased as range increases so that similar targets
are displayed in the similar intensities irrespective of the ranges to them.
The CSH-5L/CSH-8L incorporates two TVG functions, NEAR and FAR, and they
mainly compensate for propagation loss on short and long ranges respectively,
centered at the ranges shown below.
NEAR
FAR
300 m
How TVG works
The TVG is also used to suppress unwanted echoes and noise which appear in
a certain range area on the screen such as sea surface reflections and cruising
noise. To obtain the proper TVG setting, follow the procedure below.
1. Press the MENU key.
2. Use the [RANGE] control to choose [MENU MODE] at the top of the screen.
3. Use the [GAIN] control to choose SONAR to display the SONAR menu.
4. Use the [RANGE] control to choose TVG NEAR.
5. Use the [GAIN] control to adjust gain.
6. Use the [RANGE] control to choose TVG FAR.
7. Use the [GAIN] control to adjust TVG FAR (setting range: 0-10).
8. When sea surface reflections or plankton layers disturb the picture, adjust
TVG NEAR to eliminate them. They will be eliminated by decreasing the
setting by “1” or “2.”