Furuno GP-3500F - Manual (Page 187)

11. VIDEO SOUNDER OPERATION
11-15
11.4.4 Adjusting gain
Adjust the sensitivity of the receiver so excessive noise just disappears from the
screen.
CAUTION
Use the proper gain setting.
Incorrect gain may produce wrong depth
indication, possibly resulting in a
dangerous situation.
Gain too high Gain proper Gain too low
Example of proper and improper gain levels
1. Press the [GAIN] key to show the GAIN window. For dual-frequency display,
press the key again if necessary to select the frequency.
GAIN 200kHz
TURN KNOB TO
ADJUST GAIN.
HIGH
LOW
Current setting 6.0
Gain window (ex. 200 kHz)
2. Rotate the [ENTER] knob to set gain. (0.0 to 10.0).
Note: This setting must be done within 10 seconds after pressing the [GAIN]
key, otherwise the window will be erased.