Furuno GP-1650WDF - Manual (Page 80)

11. CUSTOMIZING YOUR UNIT
11-10
SYSTEM SETUP menu description
FISH ALM LVL:
Sets the fish alarm
sensitivity; namely, which echo strength will
trigger the alarm. HIGH, only the strong
echoes (red and reddish brown) trigger the
alarm; NORMAL, echoes from strong to
medium strength (greater than yellow) trigger
the alarm, LOW, any echo (greater than
light-blue) triggers the alarm.
TX POWER:
Turns TX power on/off.
TVG 200kHz, TVG 50kHz:
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.
Fish school B
Fish school A
TVG concept
ECHO OFFSET 200kHz,
ECHO OFFSET 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,
adjust echo offset to compensate for too
weak or too strong echoes.
SEABED LVL 200kHz, SEABED LVL
50kHz:
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. Note that
if the level is set too
high bottom echoes
cannot be acquired and if set too low
regards the fish school as the bottom, so the
depth indication will not be fixed. The default
setting for both 200 kHz and 50 kHz is 80.