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4-1
FINE TUNING THE PICTURE
Eliminating Unwanted Feeble Echoes
Echoes from targets such as seabed and fish return to the trans-
ducer 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 he can not
judge the actual size of the target from the size of echoes dis-
played 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 range is sup-
pressed and gradually increased as range increases so that simi-
lar targets are displayed in the similar intensities irrespective of
the ranges to them.
The CSH-7 has 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. The higher the
TVG setting the greater the amplification of echoes.
About 100 m
Near
Far
Figure 4-1 Principle of TVG
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 set TVG properly, do
the following:
How to adjust TVG
1. Press the MENU key to display the Scan menu.
2. Set both TVG NEAR and TVG FAR to “5”. These are the
standard settings and you can maintain them in most cases.
3. When sea surface reflections or plankton (displayed in weak
colors) disturb the picture, decrease TVG NEAR by 1 or 2 to
eliminate it.