Furuno 821, 841 manual STC MAN Auto, Adjusting GAIN, STC, A/C Rain and FTC

2.8Adjusting GAIN, STC, A/C RAIN and FTC

General procedure

The [ECHO] key enables adjustment of the gain, STC, A/C RAIN and FTC.

1)Press the [ECHO] key. The following dis- play appears.

GAIN ◆ [MAAUTNO		1	2	3	Item selected
STC ◆ [MANAUTO					for adjustment
		1	2	3
A/C RAIN	00
FTC	0 1 2
12					Current
					level

ECHO KEY

TO EXIT

Figure 2-4 Display for adjustment of

GAIN, STC, A/C RAIN and FTC

2)Press the cursor pad to select item to ad- just. Current selection is circumscribed by dashed rectangle.

3)Press [ENT].

3)Press the cursor pad to set level.

4)Press the [ECHO] key to finish.

How to adjust the gain (sensitivity)

How to adjust STC (suppressing sea clutter)

Echoes from waves can be troublesome, covering the central part of the display with random signals known as sea clutter. The higher the waves, and the higher the scan- ner above the water, the further the clutter will extend. Sea clutter appears on the dis- play as many small echoes which might af- fect radar performance. (See the left-hand figure in Figure 2-5).

The STC reduces the amplification of ech- oes at short ranges (where clutter is the great- est) and progressively increases amplification as the range increases, so am- plification will be normal at those ranges where there is no sea clutter. The control is effective up to about 4 miles.

STC can be adjusted automatically or manu- ally. For manual adjustment, first adjust the gain and then transmit on short range. Ad- just the STC level such that the clutter is broken up into small dots, and small targets become distinguishable. If the setting is set too low, targets will be hidden in the clutter, while if it is set too high, both sea clutter and targets will disappear from the display. In most cases adjust so clutter has disap- peared to leeward, but a little is still visible windward.

If there is no clutter visible on the display, turn off the circuit.

The gain works in precisely the same man- ner as the volume control of a broadcast re- ceiver, amplifying the signals received.

You can adjust the gain automatically or manually. For manual adjustment, adjust the sensitivity on the highest range—the back- ground noise is clearer on that range. The proper setting is such that the background noise is just visible on the screen. If you set up for too little gain, weak echoes may be missed. On the contrary excessive gain yields too much background noise; strong targets may be missed because of the poor contrast between desired echoes and the background noise on the display.

Sea clutter at	STC adjusted;
display center	sea clutter suppressed.

Figure 2-5 Effect of STC

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