68 seamanship secrets
ADJUSTING FOR RAIN, SQUALL, WAVES, AND SWELL
Water droplets, when massed together, provide an excellent reflective surface.
Rain and squalls appear as clusters of dots anywhere on the scope. Sea waves
appear as a mass of clutter at the center of the scope. Make rain clutter (FTC)
or sea clutter (STC) adjustments in small increments. The rain clutter control
clears interference over the entire scope at once; the sea clutter control clears
clutter from the scope center outward.
Use a turn-stop-watch method of incremental adjustment with any control.
Crank a tad and stop cranking. Watch the scope for several sweeps. Wait for a
target to paint more than once in the same spot. If you see nothing, repeat the
turn-stop-watch method. Easy does it. You want to adjust for the best picture
without washing out small, hidden targets.
PROPER GAIN ADJUSTMENT
Gain determines the ability of your radar receiver to amplify a signal refl ected
from a vessel, landmass, or buoy. Concentrate on properly adjusting the gain con-
trol. Good gain adjustment rewards you with three vital features for safety:
- Detection of long- and short-range targets.
- Separation of targets close to one another. For example, two vessels
close together appear as individual targets instead of as one large target. - Acquisition of weak refl ection targets (wooden vessels, targets with
round versus fl at surfaces).
How to Adjust Your Gain for the Best Picture
Try to adjust gain in relatively calm weather with no rain or wave activity.
- Turn off the rain and sea clutter controls.
- Turn the gain control down all the way.
- Set the range scale to the maximum for your vessel, based on your
antenna height (see Appendix I for a table). Find a distant object just
inside this range. - Turn up the gain very slowly until you just begin acquiring your
selected target. You should see a light speckle of dots on the scope. - Reset brightness and contrast collectively for the best picture. Take care
not to wash out small targets with too much brilliance or lose them
with too little brilliance. - Mark the gain setting on the radar with tape or a felt-tip pen. Th at way
you can quickly return to the proper setting aft er changing gain or
range scales. Lower the gain a bit when trying to pick up closer targets;
raise it for distant targets.