Furuno GP-3500F-D Operator's Manual page 212

11. VIDEO SOUNDER OPERATION
FISH ALARM LEVEL
Sets the alarm sensitivity, that is, the minimum echo strength which will trigger
the fish alarms.
HIGH: Red and stronger echoes trigger the alarm.
MED: Yellow and stronger echoes trigger the alarm.
LOW: Blue and stronger echoes trigger the alarm.
TRANSMISSION
Turns TX power on/off.
Normally, "1" should be selected. To stop the transmission, select "2". When
turning the power off and on it again, "1" is selected automatically.
TRANSMISSION POWER
Sets transmission power to HIGH or LOW.
Normally, select "1". When the gain becomes too high at the shallower, select
"2".
TVG (200 kHz, 50 kHz)
TVG (Time Varied Gain) compensates for propagation attenuation of the
ultrasonic waves. It does this by equalizing echo presentation so that fish
schools of the same size appear in the same density in both shallow and deep
waters. In addition, it reduces surface noise. Note that if the TVG level is set too
high short range echoes may not be displayed.
ECHO OFFSET (200 kHz, 50kHz)
If the on-screen echo level appears to be too weak or too strong and the level
cannot be adjusted satisfactorily with the gain control on the display unit, adjust
echo offset to compensate for too weak or too strong echoes.
BOTTOM LEVEL (200 kHz, 50 kHz)
If the depth indication is unstable in automatic operation or the bottom echo
cannot be displayed in reddish-brown by adjusting the gain control in manual
operation, you may adjust the bottom echo level detection circuit, for both 50
kHz and 200 kHz, to stabilize the indication.
11-36
NOTE
If the BOTTOM LEVEL is set too low,
weak echoes may be recognized as the
sea bottom, and the depth indication may
be unstable. Reversely, if the setting is too
high, the depth indication will not be
displayed.