Japan Radio Co. JMR-611, Instruction Manual

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3.4.5 Control Sensitivity [GAIN]
If the gain is too high, unnecessary signals including receiver noise and false
video increase resulting in reduction of visibility of targets.
On the contrary, if the gain is too low, targets including ships and dangerous
objects may not be clearly indicated.
Procedures 1 Adjust noise of the display by turning the [GAIN] dial until targets
can be easily observed.
Turning
[GAIN] dial clockwise increases gain.
Turning [GAIN] dial counterclockwise decreases gain.
By increasing receiving gain, the range to observe radar video is widened. To observe densely
crowded targets or short-range targets, reducing the receiving gain will enable the targets to be
easily observed.
3.4.6 Sea Clutter Suppression[SEA]
When using the [SEA] function, never set the suppression level too high
canceling out all image noises from the sea surface at close range.
Detection of not only echoes from waves but also targets such as other ships
or dangerous objects will become inhibited.
When using the [SEA] function, make sure to choose the most appropriate
image noise suppression level.
Procedures 1 Adjust the sea clutter returns of the display by turning the [SEA] dial
until targets can be easily observed.
Turning
[SEA] dial clockwise suppresses sea clutter returns.
Turning [SEA] dial counterclockwise intensifies sea clutter returns.
The sea clutter suppression function suppresses sea clutter returns by decreasing the receiving
sensitivity on a short range.
Turning the
[SEA] control clockwise heightens the effect of sea clutter suppression.
However, be careful that excessive suppression causes low signal-strength targets such as
buoys and boats to disappear from the radar display.