Furuno CH-37 - Manual (Page 28)

2-12
0 10
DIMMER
0 10
BRILL
HUE E/S
FAST
SCAN
TRACK V:H
RANGE
AUTO
TRAIN
DEGAUSS
BOTTOM MODE
MENU
MENU
MENU : SONAR BOTTOM/3D E/S
TX RATE : 10
TX PULSE LENGTH : LONG SHORT
TX OUTPUT POWER : A B C(MAX)
Figure 2-10 How to reduce bottom and surface reflections by
reducing Tx output power
2.11 Suppressing Bottom Tail
As described earlier, fish schools near the bottom are some-
times difficult to detect because you have to discriminate fish
echoes from the bottom reflections. To discriminate fish echoes
near the bottom, select the short Tx pulse length on the SONAR
menu to decrease the tail of bottom reflection.
2.12 Displaying Surface Fish Clearly (TVG adjustment)
Echoes from targets (such as the bottom or a fish) return to the
transducer in order of the distance to them, and when their in-
tensities are compared 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
won’t be able to judge the actual size of the target from the size
of echoes displayed on the screen. To overcome this inconve-
nience, use the TVG function. It compensates for propagation
loss of sound in water: amplification of echoes on short range is
suppressed and gradually increased as range increases so that
similar targets are displayed in similar intensities irrespective of
the ranges to them.