SONAR User Manual
15
4.3 Bottom Level
If the depth indication is unstable or the seabed
cannot be displayed steadily notwithstanding the
adjustment of the control panel, you may adjust
the bottom echo level.
CAUTION
If the level is set too low, the FE-700
may not be able to distinguish the
bottom from fish echo and the
depth indication may be unstable
and if set to high the depth
indication does not appear.
1. Press the MUTE ALARM key three times at
the EXTENSION MODE. The start-up screen
appears and shortly thereafter the BOTTOM
LEVEL display appears.
BOTTOM LEVEL
200kHz = 80 (20∼200)
-
+: 200kHz*
*: Either 200 kHz or 50 kHz is displayed
depending on which frequency is used.
2. Set the level with the [+] or [
-
] key. The
default level is 80.
3. Press the POWER switch to finish the
adjustment. Wait about 5 s and then turn on
the power again.
4.4 TVG Level
TVG (Time Varied Gain) compensates for
propagation attenuation of the ultrasonic waves,
reducing surface noise to provide a smooth
display. The TVG lowers receiver sensitivity at
the time of pulse emission and gradually
increases it with time, thereby making objects of
same reflectivity at different depths appear at the
same intensity or colors on the display. The TVG
working depth is down to approximately 150 m
on the 200 kHz system and 350 m on the 50 kHz
system. Outside this range the echoes from the
seabed and fish schools are received in full level.
There is no perceivable deterioration in
performance.
1. Press the DRAFT key three times at the
EXTENSION MODE display. The TVG
SELECT window appears.
TVG SELECT
200kHz = 5 (0∼9)
-
+: 200kHz
2. Set the TVG curve with [+] or [
-
]. The default
level is 5. Attenuation compensation curve is
at 20LogR curve.
3. Press the POWER switch to finish the
adjustment. Wait 5 s, and then turn it on
again.
4.5 Echo Offset
The echo offset feature functions to compensate
for too weak or too strong echo level. 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, do the
following to adjust echo level.
1. Press the DIM key three times at the
EXTENSION MODE display. The ECHO
OFFSET screen appears.
ECHO OFFSET
200kHz: 0 (
-
99∼+99)
-
+: 200kHz
2. Set the offset with [+] or [
-
]. The default
value is 0.
3. Press the POWER switch to finish the
adjustment. Wait about 5 s and then turn it
on again.