Furuno MODEL CSH-73 Operator's Manual page 22

3-2
Figure 3-2 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. Open sub panel 2.
2. Select TVG•TX.
3. Set TVG NEAR, MEDIUM and FAR to 5 (default setting).
There setting are useful for almost cases.
4. When sea surface reflections or plankton layers disturb the
picture, decrease appropriate TVG option by one or two steps
by pressing – (minus) key.
5. Locate fish school on a long range setting (about 800 meters)
which is approaching own ship.
6. Adjust the tilt to keep the fish school in the center of the
sonar beam, namely, fish school is displayed in strongest
colors possible. Confirm that the fish echo is displayed in
the same color as it approaches. If the color suddenly changes
to weaker colors as the fish enters MEDIUM and NEAR ar-
eas, the TVG is improperly set. Adjust the TVG. If this pro-
duces sea surface reflections and noise try to remove them
with AGC and NL controls.
Note: If the above procedure does not produce satisfactory re-
sults, the TVG curve can be changed on the SYSTEM menu.
The 25 log setting is useful for searching fish schools near shore-
lines or shallow waters.