Furuno CH-37 - Manual (Page 29)

2-13
In the CH-37, the TVG LEVEL and TIME controls compensate
for propagation loss. The effective distance is up to 1000 m
approximately.
Without TVG function Proper TVG setting
Noise caused by
strong reflection
of surface
turbulence.
Nearer target
echoes appear
in larger size.
Reduce
gain for
nearby
areas,
using
TVG.
Echoes of equal
size targets are
presented in the
same color and size.
Noise is rejected.
Position TVG Range
0
2
3
5
10 0 m
60 m
130 m
300 m
1000 m
0 10
LEVEL
0 10
TIME
TVG
Figure 2-11 How to adjust TVG
The TVG also functions to suppress unwanted echoes and noise
which appear in a certain range area on the screen as shown
in the figure above.
To adjust the TVG;
1. Set TVG time between 3 and 5 (approx. 130-300 m). This
is the standard setting and you can maintain it in most cases.
2. When sea surface reflections or plankton layers disturb the
picture, set the TVG level control around 5 to eliminate them.
3. Locate a fish school on a long range setting which is ap-
proaching your vessel. Adjust the tilt to keep the fish school
in the center of the sonar beam. Check that the fish echo
appears in the same color while it approaches. If the color
changes suddenly to weaker colors as the fish echo nears,
the TVG is improperly set. Adjust the TVG level to correct it.
If sea surface reflections and noise remain, try to remove
them with the interference rejector (“IR” on the SONAR
menu) and NL control as described on page 2-8.