Furuno MODEL CSH-73 - Manual (Page 21)

3-1
FINE TUNING THE PICTURE
This chapter provides the information necessary for tuning the
sonar picture. All operations are performed on sub panel 2 (data
setting window).
Sub Panel 2
Figure 3-1 Display unit
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-73 has three TVG functions, NEAR, MEDIUM and
FAR, and they mainly compensate for propagation loss on short,
middle and long ranges respectively, centered at the ranges shown
in the figure on the next page. The higher the TVG setting the
greater the amplification of echoes.