Furuno CH-250 - Manual (Page 60)

3-10
3.11 Adjusting the Picture
3.11.1 Displaying weak echoes clearly
Echoes from targets (such as the bottom or a fish) return to the transducer in order of the
distance to them, and when their intensities 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 inconvenience, 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.
The TVG also functions to suppress unwanted echoes and noise which appears in a certain
range area on the screen.
To adjust TVG:
1. Press the [MENU] key to open the menu.
2. Press to select MENU and then press or to select the VERT menu.
TVG LEVEL 4.0
TVG DISTANCE 4.0
GAIN ADJUST 0
RES. COLOR LOG
CLUTTER 0
HORZ RANGE x1
: SELECT : CHANGE MENU: END
MENU COM1 VERT ES PRESET SYS COM2 HORZ
Figure 3-13 VERT menu
3. Press or to select TVG DISTANCE and press to show the following dialog box.
4.0
200m
TVG DISTANCE
Hi
Lo
GAIN